Review Article Phylogenomic Investigation of Phospholipid Synthesis in Archaea - Hindawi

14 Pages·2014·1.38 MB·English

HindawiPublishingCorporation
Archaea
Volume2012,ArticleID630910,13pages
doi:10.1155/2012/630910
Review Article
Phylogenomic Investigation of Phospholipid Synthesis in Archaea
JonathanLombard,Purificacio´nLo´pez-Garcı´a,andDavidMoreira
Unit´ed’EcologieSyst´ematiqueetEvolution,CNRSUMR8079,Universit´eParis-Sud,91405OrsayCedex,France
CorrespondenceshouldbeaddressedtoDavidMoreira,[email protected]
Received8August2012;Accepted3September2012
AcademicEditor:AngelaCorcelli
Copyright©2012JonathanLombardetal. This is an open access article distributed under the Creative Commons Attribution
License,whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperly
cited.
Archaeahaveidiosyncraticcellmembranesusuallybasedonphospholipidscontainingglycerol-1-phosphatelinkedbyetherbonds
to isoprenoid lateral chains. Since these phospholipids strongly differ from those of bacteria and eukaryotes, the origin of the
archaealmembranes(andbyextension,ofallcellularmembranes)wasenigmaticandcalledforaccurateevolutionarystudies.
Inthispaperwereviewsomerecentphylogenomicstudiesthathaverevealedamodifiedmevalonatepathwayforthesynthesis
ofisoprenoidprecursorsinarchaeaandsuggestedthatthisdomainusesanatypicalpathwayofsynthesisoffattyacidsdevoid
ofanyacylcarrierprotein,whichisessentialforthisactivityinbacteriaandeukaryotes.Inaddition,weshowneworupdated
phylogeneticanalysesofenzymeslikelyresponsiblefortheisoprenoidchainsynthesisfromtheirprecursorsandthephospholipid
synthesisfromglycerolphosphate,isoprenoids,andpolarheadgroups.Theseresultssupportthatmostoftheseenzymescanbe
tracedbacktothelastarchaealcommonancestorand,inmanycases,eventothelastcommonancestorofalllivingorganisms.
1.Introduction in diverse archaea [14]; conversely, isoprenoids are known
to be universal although they are synthesized by non-
Archaeawereidentifiedasanindependentdomainoflifein
homologous pathways in the three domains of life, [15];
the late 1970s thanks to the characterization of differences
eventhestereochemistryoftheglycerolphosphatehassome
between their ribosomal RNA molecules and those of
exceptions,asshownbytherecentdiscoveryofarchaeal-like
bacteria and eukaryotes [1]. At that time, it was already
sn-glycerol-1-phosphatespecificlipidsinsomebacteria[16]
known that the so-called “archaeabacteria” held several
andineukaryoticendosomes[17].
atypical biochemical characteristics, of which the most
Today, thanks to the significant accumulation of com-
remarkable was their unusual membrane phospholipids.
plete genome sequence data for a wide variety of species,
Whereas all bacteria and eukaryotes were known to have
it is possible to study the major pathways of phospholipid
membranes based on fatty acids linked by ester bonds to
synthesis and their exceptions by looking at the presence
glycerol-phosphate,archaeaappearedtohavephospholipids
or absence of the corresponding genes in the different
composed of isoprenoid chains condensed with glycerol-
genomes. In addition, these data allows reconstructing the
phosphate by ether linkages [2–6]. Moreover, the archaeal
glycerol ethers contained sn-glycerol-1-phosphate (G1P), evolutionaryhistoryofeachgenebycombiningcomparative
whereasbacterialandeukaryoticonescontainedsn-glycerol- genomics and phylogenetics, namely, by using a phyloge-
3-phosphate(G3P)(forreview,see[7,8]).Thesedifferences, nomic approach. In this paper, we summarize the results
which have been at the center of an intense debate about concerning the phylogenomic studies of the biosynthesis
thenatureofthefirstcellmembranes[9],haveprogressively pathwaysofarchaealphospholipidcomponentsandprovide
been shown to be not so sharp: ether-linked lipids are some new evolutionary data about the enzymes reviewed
common both in eukaryotes (up to 25% of the total lipids in Koga and Morii [18] and Matsumi et al. [19] as likely
in certain animal cells, [10]) and in several thermophilic responsible for the assembly of archaeal lipids from these
bacteria [11–13]; fatty acid phospholipids have been found buildingblocks.
2 Archaea
2.ArchaeaPossessanAtypicalPathwayof andgenerallyrespectingthemainarchaealtaxonomicgroups
BiosynthesisofIsoprenoidPrecursors [31]. These results are consistent with the presence of a
distinctive archaeal MVA pathway in the last archaeal com-
Isoprenoidsarechainsofisopreneunitsandtheirderivatives monancestor(LACA)andsupportthatdifferentisoprenoid
and are found ubiquitously in all living beings. They are precursor biosynthesis pathways are characteristic of each
involved in very diverse functions, such as photosynthetic domainoflife:theclassicalMVApathwayineukaryotes,the
pigments, hormones, quinones acting in electron transport alternativeMVApathwayinarchaea,andtheMEPpathway
chains, plant defense compounds, and so forth [15, 20]. inbacteria.
In archaea, isoprenoids also make up the hydrophobic The origin of the archaeal MVA pathway appears to be
lateral chains of phospholipids [7]. Isoprenoid biosynthesis composite.Theenzymessharedwiththeclassicaleukaryotic
requires two isoprene activated precursors, called isopen- MVApathwaywerealsoancestralineukaryotesandbacteria
tenyl pyrophosphate (IPP) and dimethylallyl diphosphate and, therefore, they can be inferred to have been present
(DMAPP), which act as building parts. The first metabolic in the last common ancestor of all living organisms (the
pathway responsible for the biosynthesis of isoprenoid cenancestor), from which the archaeal lineage would have
precursorswasdiscoveredinyeastsandanimalsinthe1950s inherited them. The last enzymes of the eukaryotic MVA
and named mevalonate (MVA) pathway in reference to its pathwayweremostlikelypresentintherespectiveancestors
first committed precursor. Since its first description, the ofeukaryotesandbacteria,buttheirdistributioninarchaea
MVA pathway was thought to synthesize the isoprenoid isscarceandcomplex:homologuesofMDCcanbedetected
precursorsinallorganisms[20],butcloserscrutinyshowed inHaloarchaeaandThermoplasmatalesandsomeIDI1genes
its absence in most bacteria [21]. An elegant series of have been identified in Haloarchaea and Thaumarchaeota,
multidisciplinary approaches allowed in the late 1990s and although they most likely reflect recent horizontal gene
early2000sdescribinganindependentandnon-homologous transfer (HGT) events from bacterial donors, as deduced
pathwayin bacteria,the methylerythritol phosphate (MEP) from their position well nested among bacterial sequences
pathway(see[22]forreview).TheMEPpathwaywasfound in phylogenetic analyses [23, 31]. In contrast, the class
tobewidespreadinbacteriaandplastid-bearingeukaryotes, Sulfolobales contains PMK and MDC homologues which
whereas the MVA pathway was assumed to operate in robustly branch in an intermediate position between the
archaeaandeukaryotes[15,23].Intheearly2000s,archaeal eukaryoticandthebacterialsequences,suggestingthatthese
isoprenoids were thought to be synthesized through the sequencescouldbeancestralversionsthatwouldhavebeen
MVApathwaybecausethe14C-labelledintermediatesofthis lostintherestofarchaea[31].Ifthisisthecase,aeukaryotic-
pathway were shown to be incorporated into the archaeal like pathway (except for the IDI function, which remains
phospholipids[24].However,onlytwooftheenzymesofthe ambiguous)canbeproposedtohaveexistedinthecenances-
eukaryoticpathwayhavebeendescribedinarchaea[25,26]. tor. This pathway would have been replaced by the MEP
Moreover, the search of MVA pathway enzyme sequences pathway in the bacterial lineage, whereas in archaea only
in archaeal genomes revealed that from the seven enzymes the last steps were replaced by non-homologous enzymes.
acting on this pathway, most archaeal species lack the last We do not know the evolutionary forces that drove these
three of them: phosphomevalonate kinase (PMK), meval- changes;however,themevalonatekinase(MVK),PMK,and
onate diphosphate decarboxylase (MDC), and isopentenyl MDCbelongtoalargefamilyofkinases,namelytheGHMP
diphosphateisomerase(IDI1),involvedintheconversionof kinases [33], which is characterized by a high structural
phosphomevalonate into IPP and DMAPP [27]. Attempts and mechanistic conservation that contrasts with the large
to characterize these missing archaeal enzymes revealed rangeofsubstratesthattheycanuse[34].Ifweassumethat
two new enzymes: the isopentenyl phosphate kinase (IPK) ancestorsoftheseenzymeswerenotveryspecific,thiscould
andanalternativeisopentenyldiphosphateisomerase(IDI2) haveallowedsometolerancetorecruitmentofevolutionary
[28–30].Althoughthedecarboxylationreactionrequiredto unrelated enzymes not only in archaea but also in some
synthesize isopentenyl phosphate from phosphomevalonate eukaryotes that have replaced their ancestral PMK by a
hasnotbeendescribedyet,analternativefinalMVApathway non-homologousone[35,36].Inagreementwiththisidea,
involvingIPKandIDI2wasthenproposedtoexistinarchaea the archaeal IPK itself appears to be able to use different
(Figure1,[29]). substrates [37], which could have made the replacement
Takingadvantageoftherecentaccumulationofgenomic easier.
data,wecarriedoutathoroughphylogenomicanalysisofthe
pathwaysofisoprenoidprecursorsynthesis[31].Concerning
archaea, our presence-and-absence analysis extended the 3.EarlyEvolutionof
presence of the proposed archaeal alternative pathway to IsoprenoidChainSynthesis
a wide archaeal diversity. The main exception to these
observations was Nanoarchaeum equitans, which explains Once the isoprenoid precursors, IPP and DMAPP, have
the dependence of this organism to obtain its lipids from been synthesized, they still have to be assembled to make
itscrenarchaealhost,Ignicoccushospitalis[32].Phylogenetic isoprenoidchains.Theprenyltransferasesresponsibleforthis
reconstructions of the MVA pathway enzymes present in function are the isoprenyl diphosphate synthases (IPPS).
archaeasystematicallyrevealedacladeindependentfromthe Since many more complete genome sequences are now
otherdomainsoflife,representativeofthearchaealdiversity available than at the time of previous IPPS phylogenetic
Archaea 3
Hypothetical archaeal FA synthesis pathway
Archaeal MVA pathway
O
O O
CoA
CoA + CoA S
S S
Acetyl-CoA Acetyl-CoA Acetyl-CoA
AACT∗ (Starting with two acetyl-CoA) Thiolase O O
(Thiolase superfamily) (Thiolase superfamily)
CoA
O O R S
CoA 3-ketoacyl-CoA
S COOH O
Acetoacetyl-CoA COOH CoA
R S KR-PhaB
HMGS∗ Acyl-CoA (SDR superfamily)
(Thiolase superfamily)
O OHO OH O
CoA ER O CoA
HO S (SDR superfamily) R S
Hydroxymethylglutaryl-CoA R S CoA 3-hydroxyacyl-ACP
HMGR∗ Enoyl-ACP (HDotHdo-Mg sauopCe/rPfahmaJi ly)
O OH Fatty acids ?
HO OH
Mevalonate
PP
MVK∗ PP GGR#
(GHMP kinases) PP
O OH PP Saturated isoprenoids
Unsaturated isoprenoids
HOPhosphomevalonate O–P HO P
GGGPS O
Isope?ntenyl-PO–P Short chPaiPnS IsPuPpSerfamily) tra(nUsDfbeGirAaGs peG rfPeanSmyilly) HO GO1PHDHP(G1PsDnH-g/lD(yGcHe1QrPoS)l/-G1-DPH/ADH superfamily) GGGPSDGGGPS
IPK (I
O O
O–PP
Isopentenyl-pyroP(IPP) O O
IDI 2
(FMN-dep. P P
dehydrogenases) CDSA
O
O
O–PP
O
Dimethylallyl-pyroP(DMAPP) O
CDP
O CDP
CDP-alcohol
O phosphatidyl O
transferases
P rPeosildaure O
O Archaeal phospholipid P rPeosildaure
O GGR#
Polar
Archaeal phospholipid P residue
Figure 1: Biosynthesis pathways of phospholipid components in archaea. Abbreviations for the archaeal mevalonate (MVA) pathway:
AACT,acetoacetyl-CoAthiolase;HMGS,3-hydroxy-3-methylglutaryl-CoAsynthase;HMGR,3-hydroxy-3-methylglutaryl-CoAreductase;
MVK, mevalonate kinase; IPK, isopentenyl phosphate kinase; IDI2, isopentenyl diphosphate isomerase type II. GHMP, galactokinase-
homoserinekinase-mevalonatekinase-phosphomevalonatekinase;IPPS,isoprenyldiphosphatesynthases(asterisksindicateenzymesshared
with the eukaryotic MVA pathway). Abbreviations for the hypothetical archaeal fatty acid (FA) synthesis pathway: ACC, acetyl-CoA
carboxylase; PCC, propionyl-CoA carboxylase; KR-PhaB, beta-ketoacyl reductase; DH-MaoC/PhaJ, beta-hydroxyacyl dehydratase; ER,
enoylreductase;SDR,short-chaindehydrogenases/reductases.Abbreviationsforthesn-glycerol-1-phosphatesynthesispathway:G1PDH,
glycerol-1-phosphate dehydrogenase; DHQS, 3-dehydroquinate synthase; GDH, glycerol dehydrogenase; ADH, alcohol dehydrogenase.
Abbreviationsforthephospholipidassemblypathway:GGGPS,(S)-3-O-geranylgeranylglycerylphosphatesynthase;DGGGPS,(S)-2,3-di-
O-geranylgeranylglycerylphosphatesynthase;GGR,geranylgeranylreductase;CDSA,CDPdiglyceridesynthetase.(#)pointstotheabilityof
GGRstoreduceisoprenoidsatdifferentstepsinthebiosynthesispathway.Namesbetweenparenthesesindicatethefamilyorsuperfamilyto
whichbelongthearchaealenzymespostulatedtocarryoutparticularfunctionsonthebasisofphylogenomicanalyses.
4 Archaea
analyses,wepresenthereanupdatedsurveyoftheevolution relatedtotheshort-orlong-chainproductspecificity(data
of these enzymes. Although many different enzymes are not shown). To avoid the phylogenetic artifacts that can
requiredtosynthesizethewidediversityofisoprenoids,the be introduced by the high sequence divergence between
first steps are widely shared among the three domains of short-andlong-chainenzymes,wecarriedoutindependent
life [38]. They consist of the progressive addition of IPP phylogenetic analyses for each one of the two paralogues,
units(5carbonseach)toanelongatingallylpolyisoprenoid to which we will refer as short- or long-chain IPPS with
diphosphate molecule. Starting with DMAPP (5 carbons), regardtodominantfunctionsofthecharacterizedenzymes.
consecutive condensation reactions produce geranylgeranyl
However,aspreviouslymentioned[39–41],substratespeci-
diphosphate (GPP, 10 carbons), farnesyl diphosphate (FPP,
ficity exchange between short and long substrates appears
15 carbons), geranylgeranyl diphosphate (GGPP, 20 car-
to be relatively common, so these partial trees must be
bons),andsoforth.DifferentIPPSsarecharacterizedbythe
acknowledged mainly as phylogenetic groups related to the
allylicsubstratethattheyaccept(DMAPP,GPP,FPP,...)and
mostwidespreadbiochemicalfunction,butdonotdefinitely
by the stereochemistry of the double bonds, but the main
determine the substrate specificity of all their sequences,
characteristicusedtoclassifythemisthesizeoftheproducts
which can only be established by biochemical studies. In
that they synthesize: they can be short-chain IPPS (∼up to
preliminary short-chain IPPS phylogenies, long branches
25 carbons) or long-chain IPPS (>25 carbons). All IPPS
at the base of several eukaryotic paralogues evidenced for
arehomologousandshareacommonreactionmechanism.
the high divergence of these sequences. Since we were here
Short-chainIPPSmainlydifferinthesizeoftheirsubstrate-
mainlyinterestedinthearchaealsequences,weremovedthe
binding hydrophobic pocket (the smaller the pocket, the
divergent eukaryotic sequences from our analyses. Figure2
shorter the final product, [38]), but point mutations have
and Supplementary Figure 1 (see Supplementary Material
been shown to importantly impact the size of the pocket
available online at doi:10.1155/2012/630910) present the
and, thus, of their final products [39, 40]. Description of
phylogeny of some representative prokaryotic short-chain
equivalentnaturalmutationshavebeenreportedinarchaea
enzymesequences.Mostarchaealsequencesbranchtogether
[41], which argues against the possibility of inferring the
in a monophyletic group largely congruent with the main
preciseproductofagivenIPPSonlybasedonitsphylogenetic
archaeal phyla and orders, which suggests that this enzyme
position[41,42].
was present in LACA and was vertically inherited in most
The first published IPPS phylogenetic trees [42] only
archaeal lineages. Most bacterial sequences also cluster
used 13 sequences (of which 12 were short-chain enzymes)
togetheraccordingtothemainbacterialtaxonomicgroups,
and supported a split between prokaryotic and eukaryotic
suggesting the ancestral presence of this enzyme in the last
enzymes. At that time, archaeal IPPS were assumed to be
bacterial common ancestor and, given its presence also in
more ancient because they were known to provide iso-
LACA, most likely also in the cenancestor. However, some
prenoidsforseveralpathwayswhilebacteriaandeukaryotes
recent HGTs can also be pointed out from this phylogeny.
were thought to have more specialized enzymes. Later
Concerning archaea, Thermoproteales, some Desulfurococ-
phylogenetic analyses with more sequences showed two
cales,someThermoplasmatales,Methanocellapaludicolaand
groups corresponding to the functional split between short
Aciduliprofundumbooneibranchwithinthebacterialgroup,
and long-chain enzymes [41]. This was expected since the
so several HGTs can be invoked to explain this pattern,
long-chainIPPSusesupplementaryproteinstostabilizethe
although in most cases the support is weak and does not
hydrophobic substrate [38], which would logically impact
allow confidently determining the identity of the bacterial
the protein structure and therefore trigger the large diver-
donors(Figure2).
gencebetweentheshort-andthelong-chainenzymes.Inthat
Asinthecaseoftheshort-chainenzymes,mostarchaeal
work,theshort-chainenzymesformedthreegroupsaccord-
sequences also group together in our long-chain IPPS
ing to the three domains of life, which could be considered
phylogeniesand,despitetheweaklysupportedparaphylyof
as evidence for the presence of one short-chain enzyme in
the euryarchaeotal sequences, the main archaeal taxonomic
the cenancestor and its subsequent inheritance in modern
groupsareobserved(Figure3andSupplementaryFigure2).
lineages,includingarchaea.Furthermore,inthatphylogeny
Bacterial sequences also group together according to main
archaea did not branch as a basal lineage, disproving their
taxa, supporting that the respective common ancestors of
previouslyassumedancientcharacter.Inaddition,enzymes
with different product specificities branched mixed all over bacteria and archaea, and thus likely also the cenancestor,
hadalong-chainIPPSenzymethatwasinheritedinmodern
the tree, supporting the product plasticity of the ances-
organisms. Contrary to short-chain IPPS, eukaryotic long-
tral short-chain enzyme and the subsequent evolution of
particular specificities according to biological requirements chainIPPSarelessdivergent,sotheywereconservedinour
in modern organisms [41]. Archaeal long-chain IPPS had analyses.Surprisingly,alltheeukaryoticsequences,including
not been detected in that study, but some of them were those from plastid-lacking eukaryotes, branch together as
incorporatedinphylogeneticstudiessomeyearslater[23]. the sister group of cyanobacteria, except for some algae
WehavesearchedforhomologuesofIPPSinarepresen- that branch within the cyanobacterial group. In addition,
tativesetof348completegenomesfromthethreedomains some other more recent HGTs are observed, especially in
of life (including 88 archaea). A preliminary phylogenetic the archaeal Thermococcus genus, which branches close to
analysis showed that, in agreement with previous reports a very divergent sequence from the delta-proteobacterium
[23], the resulting sequences split into two clades mainly Bdellovibriobacteriovorus.
Archaea 5
Metallosphaera sedula
1 SulSfoullofobluosb uacs isdoolcfaatladrairciuuss Sulfolobales
0.89 0.62 Ignicoccus hospiItganliissphaera aggregans Desulfurococcales Crenarchaea
0.88 Hyperthermus butylicus
Aeropyrum pernix
0.96 0.96 ANciitdroilsoobpuusm sailcucsh amraovriotrimanuss Acidilobales
1 Cenarchaeum symbiosum Thaumarchaea
Thermococcus sibiricus
0.83 10.54 0.97 ThPePyryrmorocooccococccuccuus ssh agobariymksosmishaitiolerans Thermococcales
Methanocaldococcus infernus
Methanocaldococcus vulcanius
1 Methanocaldococcus jannaschii Methanococcales
Methanothermococcus okinawensis
0.87 10.94 MethManeotchoacncoucso mccaursi paaeolulidciuss
0.88 0.99 0.7 MethanoMpyertuhsa knaoMnMthdeeeltetrhhrmaianonbooatshpcetherarm emruasa srftebarudvritgdmeunassnisae MMeetthhaannoopcoybraalcetseriales Archaea
Methanobrevibacter smithii
Ferroglobus placidus Euryarchaea
0.92 1 0.83 AArrcchhaaeeoogglolobbuuss p fruolfguidnudsus Archaeoglobales
Methanoculleus marisnigri
Methanosphaerula palustris
0.99 1 Methanospirillum hungatei
Methanoplanus petrolearius Methanomicrobiales
0.94 0.820.86 0.9 HaloquadrMateutmha nwoarlsebgyuila boonei Methanocorpusculum labreanum
1 HaNloabtaroctneormiuomn asps .pharaonis Halobacteriales
0.96 Halomicrobium mukohataei
Methanosaeta thermophila
0.96 0.95 0.99 MMMeetehtthahananonocoossacacrrcociiindnaeas b abacurerkttieovrnoiriians Methanosarcinales
Bacteroidetes (6)
1
1 LentisphaVeircat iavraallnise ovsaadensis Lentisphaerae
Collinsella aerofaciens Actinobacteria
0.96 1 Spirochaeta smaragdinae DeinococcuSsp-Tirhoecrhmaeutes s(3)
0.96 Bifidobacterium adoAlecstcinenotmisyces coleocanis Actinobacteria
Myxococcus xanthus Deltaproteobacteria
0.92 0.83 0.94 FrankBirae vailbnaicterium linens Actinobacteria
Staphylothermus marinus Desulfurococcales
0.97 1 AciduliprofundumT bhoeornmeoisphaera aggregans (Crenarchaea) Archaea
0.99 0.99 ThermoplasmFear rvooplclaasnmiuam acidarmanus T(Ehuerrymarocphlaaesma)atales
1 0.98 0.97Thermofilum TphenerdmenPospyVrrooutblecauacsnu tilesuanmeat xaca dliidstirfoibnutitsa T(Chreernmaorcphraoetae)ales Archaea Bacteria
0.79 Caldivirga maquilingensis
Frankia alni Actinobacteria
Dictyoglomus thermophilum Dictyoglomi
0.92 Thermomicrobium roseum
0.92 Anaerolinea thermophila
0.73 Methanocella paludicola Euryarchaea Chloroflexi
0.65 0.72 0.99 HerpCehtolosripohfloexnu asu aruarnatniaticaucsus
Other bacteria (59)
0.93
0.3
Figure2:Short-chainIPPSphylogenetictreereconstructedusing136representativesequencesand244conservedsites.Multifurcations
correspond to branches with support values <0.50. Triangles correspond to well supported-bacterial clades (numbers in parentheses
correspondtothenumberofsequencesincludedintheseclades).Forthecompletephylogeny,seeSupplementaryFigure1.
Altogether, these results support that in spite of some archaeallipidmetabolismisbasedonisoprenoids,avariety
recent HGTs from bacteria to archaea, most archaea have of experimental approaches have shown that fatty acids
homologuesofboththeshort-andthelong-chainIPPSthat (FA) also exist in these organisms. Archaea show variable
wereinheritedfromLACAandthat,mostlikely,werealready concentrations of free FA or their derivatives [4, 24, 43–
presentinthecenancestor. 45], which has stimulated some attempts to biochemically
characterize an archaeal FA synthase [46, 47]. Archaeal FA
4.ArchaeaMayHaveanACP-IndependentFatty can participate in protein structure [48–50] and acylation
AcidBiosynthesisPathway [47] but they have also been found as components of
membrane phospholipids in very diverse euryarchaeotes
In bacteria and eukaryotes, fatty acids are components of [14]. Therefore, it is not surprising that homologues of
membrane phospholipids, energy-storage molecules, sub- several of the enzymes involved FA biosynthesis in bacteria
strates for post-translational modifications of proteins, sec- had been detected in archaeal genomes [8, 51]. In bacteria,
ondary metabolites, and components of coenzymes and FA biosynthesis occurs through multiple condensations of
messengercompounds.Despitethegeneralassumptionthat acyl groups (malonyl-CoA) in a series of cyclical steps.
6 Archaea
Methanocella paludicola Methanocellales
Haloquadratum walsbyi
1 Halogeometricum borinquense
1 Haloferax volcanii
0.54 Halorubrum lacusprofundi
0.66 0.9 Natronomonas pharaonis
Halorhabdus utahensis
0.96 Haloarcula marismortui Halobacteriales
0.90.98 HaloHmailcorboabcituemri ummu kspo.hataei
0.98 Halalkalicoccus jeotgali
0.65 Haloterrigena turkmenica
0.98 Natrialba magadii
Ferroplasma acidarmanus Euryarchaea
1 PicrophTilhuesr tmororpidlaussma acidophilum Thermoplasmatales
1 Thermoplasma volcanium
Archaeoglobus profundus
10.94 FerroAgrlochbaueso pgllaocbiudsu sfulgidus Archaeoglobales
0.99 Methanocella paludicola Methanocellales
Methanosaeta thermophila
0.890.8 0.940,86 MethMaMnetoeMhhtahaenatlohonbcaooinhucoacmsolaoi epdrcvheiesins lbuatiu sgb ramattoruaknmheiiirii Methanosarcinales Archaea
0.98 0.9 0.187 MMethetahnaonsoasracirncian aac metaivzoerians
Korarchaeum cryptofilum Korarchaea
0.98 1 CNenitarrocshoapeuummi lsuysm mbaiorsiutimmus Thaumarchaea
Thermofilum pendens Thermoproteales
Ignicoccus hospitalis Desulfurococcales
0.98 0.83 AcidiloHbyupse srathccehrmaruosv obruatnyslicus DAceisduillfoubraolceosccales
0.81 Sulfolobus acidocaldarius
0.57 10.92 SulfolobuMs teotSkauollldofoasplioihbauesr aso slefadtualraicus Sulfolobales
0.75 Caldivirga maquilingensis Crenarchaea
Vulcanisaeta distributa
1 ThePrymroobparocuteluusm t ecnaalixdifontis
1 0.98 Pyrobaculum arsenaticum Thermoproteales
0.93 Pyrobaculum aerophilum
0.83 Pyrobaculum islandicum
0.87 Thermoproteus neutrophilus
Bdellovibrio bacteriovorus Deltaproteobacteria
0,81 0.96 0.98 TherTmhoecromccoucos cscpu.s gammatolerans T(Ehuerrymarocchoacecaa)les Archaea
0.94 FirmicuCthelso (r7o)flexi (9)
0.86 0.99 ActiFniobrboabcatectreiar s(u4c)cinogenes Fibrobacteres
0.6 0.88 0.88 Moorella thermoacetica Firmicutes
Rubrobacter xylanophilus Actinobacteria
0.81 1 Deinococcus-TLheeprtmosupsi r(a7 )interrogans Spirochaetes
0.75 0.76 0.88 Myxococcus xanthus Thermotoga maritima DTheeltramproottoegoabeacteria
0.72 1 Gloeobacter violaceus Epsilonproteobacteria (9)
Prochlorococcus marinus
0.98 1 PaulPinoerlplah ycrhar opmuraptouprehaora endosymbiont
0.91 0.804.71 0.58 1 ChMlaimcryodmComyoanonanisda pisou rsseciilhnlyahzaornd tmiierolae P(Elaunktaareyotes) Cyanobacteria
0.83 Cyanophora paradoxa
Crocosphaera watsonii
1 Cyanothece sp.
0.98 1 0.08.684 1 NAnosaAtbocaca erpnyuoanc vhcatliorfrioairsbm mileiasrina
Tetrahymena thermophila
1 Paramecium tetraurelia
Cryptosporidium hominis
0.55 0.67 0.8701.75 TLreyisphamnoasnoima am carjuoTzroixoplasma PgolansdmiBioadbieusmia fbaolcviipsarum EAxlvceaovlaattaa Bacteria
0.82 Dictyostelium discoideum Amoebozoa Eukaryotes
Aureococcus anophagefferens Stramenopiles
0.55 0.87 SchizTorsiachccohpalaroxm adychease preonmsbe Opisthokonta
0.92 PAhuyrteoopcohcthcuosr aa ninofpehstaagnesfferens Stramenopiles
0.77 Naegleria gruberi Excavata
0.890.95 ChlAamraybdidoomposinsa tsh raeliinanhaardtii Plantae
Fusobacterium nucleatum Fusobacteria
0.53 0.99 0.88 1 Spirochaeta smaragdiFniaremicutes (4) Spirochaetes
0.94 1 AcidobacGteemriam (a4t)imPVoCna gs raouurpa n(1ti1a)ca Gemmatimonadetes
0.97 0.89 0.98 1 DesulfohaloBbaicutmerL oraiewdtbesoatenesni/asCe ihnltorraoceblil u(1la6r)is Deltaproteobacteria
0.93 Aquificales (6)
0.69 Syntrophus aciditrophicus Deltaproteobacteria
Candidatus Nitrospira
0.87 0.73 Leptospirillum ferrooxidans Nitraspirae
Thermodesulfovibrio yellowstonii
0.83 0.58 0.98 1 DesulfurispirDilleufmer riinbdaicctuemrales (3) Chrysiogenetes
0.4 0.66 Alpha-/Beta-/Gamma-/Deltaproteobacteria (42)
Figure3:Long-chainIPPSphylogenetic treereconstructedusing218representativesequencesand241conservedsites.Multifurcations
correspondtobrancheswithsupportvalues<0.50.Trianglescorrespondtowell-supportedcladesoutsideArchaea(numbersinparentheses
correspondtothenumberofsequencesincludedintheseclades).Forthecompletephylogeny,seeSupplementaryFigure2.
The building blocks necessary to the activity of the FA protein (ACP), which is required to channel the elongating
synthasesareprovidedbyseveralreactions.First,theacetyl- intermediates among the FA synthase enzymes, has to be
CoAcarboxylase(ACC)convertsacetyl-coenzymeA(CoA) activated through the addition of a phosphopantetheine
intomalonyl-CoA.Second,thepeptidecofactoracylcarrier groupfromCoAtotheapo-ACPbyanACPsynthase.Finally,
Archaea 7
the malonyl-CoA: ACP transacylase (MCAT) charges the betweenarchaeaandbacteriahavebeendescribed(themost
malonyl-CoAtoholo-ACP,resultinginmalonyl-ACP. remarkable is probably the description of an archaeal-like
SincenoarchaealFAsynthasesystemhasbeendescribed G1PdehydrogenaseinthebacteriumBacillussubtilis,[60]),
in detail yet, we recently studied the evolution of the but the fact that the two dehydrogenases belong to large
archaeal homologues of the bacterial genes involved in FA enzymatic superfamilies from which they were recruited
synthesis. First, many archaea possess ACC homologues has provided a model for the independent origin of these
that are closely related in phylogenetic analyses, suggesting dehydrogenases from likely ancient promiscuous enzymes
their possible monophyletic origin and, consequently, the [8].
presenceofthisenzymeinLACA[52,53].Second,onlyafew Geranylgeranylglyceryldiphosphateanddi-O-geranylge-
unrelatedarchaealspecieshaveACPandtheACP-processing ranylglyceryl phosphate synthases (GGGPS and DGGGPS,
machinery (ACP synthase and MCAT) and phylogenetic resp.) are the enzymes that subsequently link isoprenoids
analysis suggests that they acquired them by HGTs from to glycerol phosphate in archaea [18]. Boucher et al. [23]
bacteria.Asaresult,ACPanditsrelatedenzymesaremissing found that GGGPS are widespread in archaea whereas,
inmostarchaeaandappearnottohavebeenpresentinLACA among bacteria, it was found only in Bacillales and in one
[54].FortherestofenzymesinvolvedinthecyclicstepsofFA Bacteroidetes species. They also described a very divergent
synthesis (see Figure1), phylogenetic analyses support that homologue in halophilic archaea and in Archaeoglobus.
the archaeal sequences are more closely related to bacterial Despitetheirdivergence,theseenzymesappeartocarryout
enzymesthatareactiveonsubstrateslinkedtoCoAthanto thesamefunction[61].Usinganupdatedgenomesequence
enzymes that use substrates linked to ACP. Taking this into database, we also retrieve the very divergent GGGPS in
account, we have proposed that the ACP processing system Methanomicrobiales, confirm that GGGPS is present in
has specifically evolved in the bacterial lineage and that Bacillales, and extend this observation to a surprising
archaea carry out FA synthesis using a likely ancient ACP- diversity of Bacteroidetes (Supplementary Figure 3. This
independentpathway[54].AlthoughACCexistsinarchaea, suggests that GGGPS plays an important role in these two
the hypothetical archaeal FA synthesis pathway probably bacterial groups and, indeed, it has recently been shown
involvestwoacetyl-CoAinsteadofusingmalonylandacetyl to participate in the synthesis of archaeal-type lipids of
thioesters as in bacteria, since the thiolases that carry out unknown function in these bacteria [16]. In conclusion, at
thisfunctionareknowntobedecarboxylativeinbacteriabut leastoneGGGPSgeneappearstohavebeenpresentinLACA,
non-decarboxylativeinarchaea[55]. whereas the divergent copy of this gene probably emerged
Interestingly,ithasbeenunclearforalongtimeifeither later in a more recent group of euryarchaeota. GGGPS
the bacterial FA synthesis pathway specifically recognizes were probably independently transferred to the respective
each acyl-ACP intermediate or if its enzymes randomly ancestorsofBacillalesandBacteroidetes.
fix these intermediates, modifying the correct ones and Hemmi et al. [62] carried out the first phylogenetic
releasing the inappropriate ones. Recent work has shown analysis of the DGGGPS sequences and their superfamily,
that ACP carries out its channeling function by adopting the UbiA prenyltransferase family (17 sequences branching
uniqueconformationsforeachenzymeoftheFAelongation in 6 different groups). Using all sequences available at
cycle[56].Yet,itcanbereasonablyassumedthataputative present, we retrieve similar but much more diversified
ACP-independent mechanism would rather use random groups(SupplementaryFigure4.Archaealsequencescluster
interactionsbetweenintermediatemetabolitesandenzymes, togetherinamonophyleticassemblage,suggestingcommon
whichmightbeassumedtobelessefficientthanthebacterial ancestry, although crenarchaeota are paraphyletic proba-
ACP-mediated system. Although this remains speculative bly as a result of reconstruction artifacts. A number of
and needs biochemical confirmation, the high efficiency of bacteroidetes sequences branch among the crenarchaeota,
theACP-mediatedmachinerymayexplainthepreeminence reflecting an HGT event to an ancestor of this bacte-
of FA in bacterial membranes, whereas archaea would have rial group. In addition several bacterial phyla (Chlorobi,
opted by the alternative ancestral mechanism of synthesis Cyanobacteria, Chloroflexi, Planctomycetales, and some
of lateral chains for membrane phospholipids, namely, the proteobacterial species) possess UbiA-related homologues.
isoprenoids[31],relegatingFAtodifferentcellularfunctions However,inseveralofthesebacterialspecies,theseenzymes
and,onlytoasmallextent,tomembranesynthesis[54]. areinvolvedinphotosynthesis(theytakepartinthesynthesis
of respiratory quinones, hemes, chrolophylls, and vitamin
E [62]) and it is difficult to determine if the widespread
5.LinkingGlycerolPhosphatewith distribution in bacteria is due to the ancestral presence of
theLateralChains a homologue of this enzyme in the last common bacterial
ancestorortoseveralrecentHGTstothesebacterialgroups
Although archaeal phospholipids were already known to fromarchaealdonors.
use G1P instead of G3P as bacteria and eukaryotes do, The search of homologues of the bacterial glycerol
the recent characterization and sequencing of the enzyme phosphateacyltransferasesPlsX,PlsY,PlsB,andPlsC,which
responsibleforitssynthesisinarchaea(G1Pdehydrogenase carry out the addition of fatty acids to glycerol phosphate
[57,58])wasastonishingbecausethisenzymeappearedtobe [63,64],intheavailablearchaealgenomesequencesallowed
totally unrelated to the canonical G3P dehydrogenase [59]. retrieving very few homologues, all of them most likely
Sincethen,verylittleexceptionstothisclear-cutdistinction acquiredbyHGTfrombacterialdonors(notshown).
8 Archaea
6.LinkingthePolarHeadGroups enzyme probably existed at least in the last euryarchaeotal
common ancestor. In the second tree, a larger group of
Oncethetwohydrocarbonchainsarelinkedtothephospho- archaeal enzymes, predicted to use glycerol phosphate or
lipidbackbone,twoadditionalstepsarerequiredtoaddthe myo-inositol-phosphate as substrates [69, 70], cluster in
polar head group (Figure1). First, an enzyme replaces the our analysis with bacterial enzymes that use myo-inositol,
phosphate linked to the glycerol moiety by a CDP group; but these bacterial sequences are scarce and appear to
then, this CDP is replaced by the final polar head group, have been acquired from archaea by HGT (Supplementary
which can be very diverse (glycerol, myo-inositol, serine, Figure 6). The phylogeny of archaeal sequences supports
and so forth) [18]. The first step has been biochemically the monophyly of Crenarchaeota and a patchy distribu-
described in archaea but the enzyme that carries out this tion of several paralogues in Euryarchaeota, which makes
function remains unknown [65]. The bacterial counterpart difficult the analysis of the evolution of these enzymes in
is the CDP diglyceride synthetase (CdsA) [66, 67]. We archaea without incorporating supplementary biochemical
looked for archaeal homologues of the bacterial enzyme information. At any rate, the wide distribution of this
and retrieved several sequences that we used as queries for enzyme family in archaea strongly suggests that at least
exhaustive searches in archaeal genomes. This allowed us one representative of these enzymes was already present in
to observe that this enzyme is widespread both in bacteria LACA. Whereas it was conserved in Crenarchaeota, it was
and archaea. Our phylogenetic trees show two clades that subjected to several duplication and neofunctionalization
correspond to archaea and bacteria and the phylogenetic events in Euryarchaeota, which would explain the complex
relationships within each of them are congruent with the distributionpatternobservedineuryarchaeotalspecies.
main accepted taxonomic groups (Figure4). This supports
the vertical inheritance of this gene from the cenancestor 7.SaturationofIsoprenoidChains
and, consequently, its presence in LACA. However, to our
knowledgenoarchaealCdsAhasbeenbiochemicallycharac- So far, we have described the main synthesis and link
terizedsofar,whichwouldberequiredtoconfirmthatthese mechanisms of archaeal phospholipid components, but a
archaeal homologues are responsible for the biochemical wide diversity of phospholipids actually exists in archaea
activitydescribedbyMoriietal.[65]. [71]. A substantial characteristic of archaeal membranes is
Two enzymes involved in the second step of the their saturation rate, since double bonds have a prominent
attachment of polar head groups have been characterized influenceonmembranestability[72].Mostarchaeacontain
in archaea [68, 69]. These enzymes belong to the large saturated phospholipids and the geranylgeranyl reductase
familyoftheCDPalcoholphosphatidyltransferasesandhave (GGR), the enzyme responsible for the reduction of iso-
homologuesinbacteria[70].Thebacterialmembersofthis prenoid chains, has been recently described in the eur-
enzyme family are known to have different specificities in yarchaeota Thermoplasma acidophilum and Archaeoglobus
order to add different polar head groups on phospholipids. fulgidusandthecrenarchaeoteSulfolobusacidocaldarius[73–
A previous phylogenomic survey carried out by Daiyasu 75]. These studies show that archaeal GGR are able to
et al. [70] showed that the different sequences group in use geranylgeranyl chains either isolated or attached to
phylogenetictreesaccordingtotheirpredictedsubstrates.In phospholipids as substrates. When GGPP is used as a
addition, the groups of bacterial sequences were in agree- substrate,allbondsbuttheoneinpositionC2arereduced,
mentwiththemainbacterialtaxonomicgroups.Ouranalysis allowingtheincorporationinphospholipids,butisoprenoids
with a larger taxonomic sample confirms that homologues chains that are already attached to glycerol phosphate can
of these genes are widespread in archaea. All sequences have all their double bonds reduced by this enzyme. As a
group into three main categories (data not shown), one result,isoprenoidreductioncanhappenatdifferentstepsof
relatedtotheadditionofserineasapolarheadgroup[68], thephospholipidbiosynthesispathway(Figure1).
anotherrelatedtomyo-inositol-phosphatetransfer[69](and Archaeal GGRs are homologous to previously reported
maybe also glycerol in archaea, according to classification cyanobacterial and plant GGRs involved in chlorophyll
in [70]),and the last one using glycerol.Archaea arefound synthesis [76, 77] and many different GGR paralogues
in the first two groups but not in the last one. In order have been identified in archaeal genomes that could carry
to avoid artifacts due to extreme sequence divergence, we out independent isoprenoid chain reductions [19]. Our
carriedoutphylogeniesforeachofthetwogroupscontaining phylogeny of GGRs confirms that GGRs are widespread
archaeal representatives. In the first phylogeny, archaeal among crenarchaeota and that at least two paralogues exist
sequences predicted to use serine [68] as a substrate are inawidediversityofeuryarchaeota,althoughsomearchaeal
limited to Euryarchaeota (Supplementary Figure 5). This groupsalsobearsupplementaryGGRgenes(Supplementary
tree shows a poorly supported group of slow evolving Figure 7). This supports the ancestral presence of at least
bacteriatogetherwithseveraldivergentbacterial,eukaryotic oneGGRgeneinarchaea,followedbyacomplexhistoryof
and archaeal (Methanococcoides burtonii and haloarchaea) duplicationsandHGTs.GGRsarealsopresentinmanybac-
sequences. Such mixed distribution dominated by strong terialgenomes,butseveralHGTscanbeobserved,probably
sequence divergence and HGTs contrasts with the rest of relatedtothefunctionofthisgeneinphotosynthesis,making
the phylogeny, which is congruent with the main accepted uncertaintheprimaryoriginofthisgeneinbacteria.Among
taxonomic groups. Especially, one monophyletic group of eukaryotes, only sequences from plastid-bearing organisms
euryarchaeota can be pointed out, supporting that this were detected and these sequences clearly branched within
Archaea 9
Ferroplasma acidarmanus
0.91 Picrophilus torTrihdeursmoplasma volcanium Thermoplasmata
Aciduliprofundum boonei Unclassified
Ferroglobus placidus
1 0.93 ArchaeoglobHuasl ofuqlugaiddurastum walsbyi Archaeoglobales
10.58 HHaalolobmaciNtcerraoitubriimualm bspa m. muakgoahdaitiaei Halobacteriales
0.89 0M.8e1thanoNspahtraoenroumlao pnaalsu psthraisraonis
0.88 0.920.83 MeMtheatnhoarneoguculall ebuoso nmeairisnigri Methanomicrobiales
0.81 Methanospirillum hungatei
Methanocella paludicola Methanocellales
0.840.84 MethManeothsMaarnecotihnhaaan lbooapsrahkeieltuaris t mhearhmiiophila Methanosarcinales Euryarchaea
0.64 0.91 0.83 0.96MethMManeetothphayanrnouocsca aklldadnoocdcoMloecccrecuiutshs av sunplo.ccaoncicuuss vannielii MMeetthhaannoopcoycrcaaleless
0.87 0.84 0.97 MetMhaenthoathneortmheorcmococbuas cotekrin_tahweernmsaisutotrophicus
0.95 0.902.82 KorMarecthhaaMenMueomtethht hacernarymnopsoutpboshrfi aefleveurrimvbaia dsctutaesdr tsmmainthaiei KMoertahracnhoabeaacteriales Archaea
0.78 0.901.86 00.9.6820.9T5hermPyorcPoocyTcorchcoucecsuTro msschIp cgaeou.nbrcsmiyo sfscpuoschirfiuialsoue sormunas npauegrngirdneeegnuassns TDThheeesurrmmlfuoorpcoorcococtceacalealesless
Desulfurococcus kamchatkensis
0.78 1 StapThhyelormthoerspmhuase rmaa argingruesgans
0.87 HyperthermAucsi dbiulotbyluics ussaccharovorans Acidilobales Desulfurococcales
Aeropyrum pernix
0.94 0.91 MetIaglnloicsopchcauesr ah ossepdiutalalis Crenarchaea
0.98 0.93 SuSlufolfloolboubsu sto skoolfdaataiiricus Sulfolobales
0.81 Caldivirga maquilingensis
0.980.86 0V.9u9lcanisaeta PdyiTsrPtohrybeirrabomucbutaoalpcuurmolut aemurs sie snnlaeauntitdcriuocpmuhmilus Thermoproteales
Sphingomonas wittichii
0.71 0.91 BSrpehviunngodpimyxoins aasl assukbevnisbirsioides Alphaproteobacteria
Rhizobium leguminosarum
0.71 Nitratiruptor sp.
0.97 Nautilia profundCicaomlapylobacter gracilis Epsilonproteobacteria
0.79 Arcobacter butzleri
Francisella tularensis
1 0.8 Xanthomonas oAryctzianeobacillus pleuropneumoniae
0.830.78 0.870.96 EscherichiMaD ceoetNhlcihyellioisbrsieourmimao neplaeotsnr aograleotimaphaitliucam BGeatma/maproteobacteria
Methylobacillus flagellatus
0.78 1 FranAkcitain aolmniyces coleocanis Actinobacteria
Algoriphagus sp.
0.86 0.93 PrCeyvtootpehllaa gaam hnuitichinsonii Bacteroidetes
Chloroflexus aurantiacus
0.85 KtedonobAancateerro rlainceema tifheerrmophila Chloroflexi
Petrotoga mobilis
1 0.89 Thermosipho Tafhreicramnoutsoga maritima Thermotogales
0.8 Dehalogenimonas lykanthroporepellens Chloroflexi
0.78 Isosphaera pallida
0.810.84 Pirellula staleyi Planctomyces limnophilus
Victivallis vadensis PVC group
0.66 0.87 ChthoniobaOctpeirt ufltauvsu tserrae
0.6 Lentisphaera araneosa
Acidobacterium capsulatum Acidobacteria
0.87 Moorella thermoacetica Firmicutes
Gemmatimonas aurantiaca Gemmatimonadetes
0.8 0.9 0.98 IlyobaFcutseorb paocltyetrrioupmu snucleatum Fusobacteria
0.8 Syntrophobacter fuDmeasruolxfoidhaanlosbium retbaense Deltaproteobacteria
0.96 0.910.91 TrueDpeGerienao orbcaaodccitcoeuvrsM i mcrtaerediitoxaitolhldieurrermdaunucsse rnusber Deinococcus Bacteria
Hydrogenobaculum sp.
0.89 0.82 AquifexT haeeromlicoucsrinis albus Aquificales
Mycoplasma agalactiae
0.84 0.85 UreaplasmaS ppiarorvpulamsma citri Tenericutes
0.87 1 Pirellula Rsthaoledyoipirellula baltica Planctomycetales
Eukaryotes
1
0.52
Mitsuokella multacida
0.79 0.8 CoCpraorcboocxcyuds oetuhtearcmtuuss hydrogenoformans Firmicutes
0.84 Flavobacterium johnsoniae Bacteroidetes
0.72 0.96 StreptobLaecpiltloutsr michoinai lhifoofrsmtaidsii Fusobacteria
0.910.78 0.92 0.97 BaEcniSltlteurresop sctuoocbcctouiclsic sufas eacgaalilsactiae Firmicutes
Calditerrivibrio nitroreducens Deferribacteres
0.76 Spirochaeta smaragdinae
0.97 TreBpoornreemliaa bduerngtdicoorlfaeri Spirochaetes
0.73 GloeobacterC vhiloalmacyeduisa trachomatis Chlamydiales
0.902.67 0.980.8005.9.532 NAocasCtroyCyCcoa hhcpnlhluooolnrtroohocrbetbisiciaf ueomPc mrusrampol urt.seietmnhpaie pdcaourcmhvulomris aestuarii CCyhalonroobbaicteria
0.81 Anaerobaculum hydrogeniformans
0.99 0.9 AminTohbearcmtearinuamer ocovliobmriob iaencisdeaminovorans Synergistetes
0.5
Figure4:CdsAphylogenetictreereconstructedusing133representativesequencesand87conservedsites.Brancheswithsupportvalues
<0.50havebeencollapsed.Forthecompletephylogeny,seeSupplementaryFigure8.
10 Archaea
onegroupofcyanobacterialsequences,thussupportingthe Acknowledgments
plastidialoriginofthesegenesineukaryotes.
TheauthorsthankA.Corcellifortheinvitationtocontribute
thispaper.Thisworkwassupportedbytheinterdisciplinary
8.Discussion
programs Origine des Plane`tes et de la Vie and InTerrVie
Incontrastwiththeratherimpressiveknowledgeaboutthe (Interactions Terre-Vie) of the French Centre National de
biochemistry and biosynthesis of bacterial cell membranes, laRechercheScientifiqueandInstitutNationaldesSciences
many aspects of their archaeal counterparts remain to be de l’Univers and by French National Agency for Research
elucidated.Eventhesynthesisofthemostcanonicalarchaeal (EVOLDEEP Project, contract no. ANR-08-GENM-024-
membrane lipids, the phospholipids based on isoprenoid 002). J. Lombard is recipient of a Ph.D. fellowship of the
lateral chains, still has some unresolved points, such as the FrenchResearchMinistry.
identityoftheenzymecarryingoutthephosphomevalonate
decarboxylase activity necessary for the final steps of the References
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