Recent Advances in Structural Research on Ether Lipids from Archaea Including Comparative and

16 Pages·2005·0.19 MB·English

Biosci.Biotechnol.Biochem.,69(11),2019–2034,2005
Review
Recent Advances in Structural Research on Ether Lipids
from Archaea Including Comparative and Physiological Aspects
Yosuke KOGAy and Hiroyuki MORII
Department of Chemistry, School of Medicine, University of Occupational and Environmental Health,
Kitakyushu 807-8555, Japan
A great number of novel and unique chemical published,avarietyofcorelipidsandlipidswithunique
structures of archaeal polar lipids have been reported. polar groups were reported successively. The lipid
Since 1993, when those lipids were reviewed in several structures which have been identified in archaea up to
review articles, a variety of core lipids and lipids with now are summarized in Table 1, which shows the
unique polar groups have been reported successively. distribution of lipid component parts but not exact
We summarize new lipid structures from archaea structuresinalltheknownfamiliesofarchaea.Archaeal
elucidated after 1993. In addition to lipids from intact lipids are generally composed of a core lipid (archaeol
archaeal cells, more diverse structures of archaea- or caldarchaeol) and phosphodiester bonded polar head
related lipids found in environmental samples are also groups or glycosides that are linked to one of the core
reviewed. These lipids are assumed to be lipids from lipids.Therefore,ifoneknowsthelipidcomponentparts
unidentifiedorancientarchaeaorrelatedorganisms.In in a given species of archaea, one can assume the lipid
the second part of this paper, taxonomic and ecological structures present in that species. Because the compo-
aspects are discussed. Another aspect of archaeal lipid sition of lipid component parts is widely shared by
study has to do with its physiological significance, archaea species belonging to the same family, Table 1
particularly the phase behavior and permeability of shows the family-level distribution of lipid component
archaeallipidmembranesinrelationtothethermophily parts, even though the phylogenetic relationship of the
of many archaea. In the last part of this review we lipid composition of species of crenarchaeota is not
discuss this problem. unambiguously established. Up to now, minimal infor-
mation on lipid components has been reported for at
Key words: archaea; ether polar lipid; structure deter- least one organism of all but one archaeal family
mination; chemotaxonomic marker; heat- (Thermofilaceae). Recent studies on methanogens lipids
tolerant membrane revealed that they reflect the phylogenetic relationship
of archaeal organisms and that they can be a tool for
Since 1962, when Kates et al. found a diether-type taxonomic and ecological studies of Archaea.8)
phospholipidinanextremelyhalophilicmicroorganism, In this article, first we summarize recently elucidated
Halobacterium cutrirubrum,1) over 100 ether-type polar structures of new core lipids and polar lipids from
lipids (phospholipids, glycolipids, and phosphoglycoli- archaea since publication of the reviews in 1993.6,7) In
pids) have been identified in various archaea. The time addition to lipids from intact archaeal cells, more
when the first diether-type phospholipid was found in diverse structures of archaea-related lipids were found
Halobacterium wasfar before the concept ofarchaea or from environmental samples, which are also reviewed,
archaebacteria was proposed. Soon after Woese et al.2) because they are assumed to be lipids from unidentified
proposed that methanogens should be classified in a orancient archaea orrelatedorganisms. Inthe nextpart
completely separate group as archaebacteria (later re- of this review, taxonomic and ecological aspects are
named archaea3)) in 1977, ether-type lipids were discussed. The physiological significance of archaeal
recognized as one of the most characteristic markers lipids is discussed in relation to the heat-tolerance of
of archaeal cells. Since lipids of thermoacidophiles archaeal lipids in the last part of this review.
(Sulfolobus and Thermoplasma) and methanogens as
wellasextremehalophileswereidentifiedasisoprenoid- I. New Core Lipids
glycerol ethers, these microorganisms were also classi-
fied in archaea. Throughout the 1980s and the 1990s, a Isocaldarchaeol
greatnumberofnovelanduniquechemicalstructuresof Thestructureofcaldarchaeolwasfirstproposedtobe
archaeal polar lipids were reported and reviewed in anantiparallelarrangementofthetwoglycerolunitsfor
several review articles.4–7) After the reviews were Thermoplasma acidophilum tetraether lipid shown in
y Towhomcorrespondenceshouldbeaddressed.Fax:[phone];E-mail:[email protected]
Abbreviations:TLC,thin-layerchromatography;GLC,gas-liquidchromatography
2
0
2
0
Table1. DistributionofLipidComponentPartsinArchaea
Alineinwhichonlyafamilynameisshownrepresentscommondistributionoflipidcomponetpartsinanumberofspeciesofthefamily.
Corelipid
Archaealfamily Archaeol Caldarchaeol PhospholipidHeadGroup GlycolipidSugar
Ar HO C25 Cyc Usat CA Ring H Ctol Ino Et Ser Gro APT Cho Glc Gal Man GN Gul Sul Reference
Halobacteriaceae + (cid:1) ((cid:1)) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) + + + (cid:1) (cid:1) + 6
Methanobacteriaceae + (cid:1) (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) (cid:1) + + + (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) 8
Methanothermaceae + (cid:1) (cid:1) (cid:1) (cid:1) + (cid:1) + (cid:1) + + (cid:1) (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) + (cid:1) (cid:1) 8,33
Methanococcaceae + + (cid:1) (cid:1) (cid:1) ((cid:1)) (cid:1) (cid:1) (cid:1) (cid:1) (+) + (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) + (cid:1) (cid:1) 8
Methanocaldococcaceae + (cid:1) (cid:1) + (cid:1) (+) (cid:1) (cid:1) (cid:1) (cid:1) + + (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) + (cid:1) (cid:1) 8
Methanomicrobiales + (cid:1) (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) + + (cid:1) + + (cid:1) (cid:1) (cid:1) (cid:1) 8
Methanopalnaceae + (cid:1) (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) + + (cid:1) + + (cid:1) (cid:1) (cid:1) (cid:1) 8
Methanocorpusculaceae + (cid:1) (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) + + (cid:1) + + (cid:1) (cid:1) (cid:1) (cid:1) 8
Methanospirillaceae + (cid:1) (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) + + (cid:1) + + (cid:1) (cid:1) (cid:1) (cid:1) 8 Y
.
Methanosarcinaceae + (+) (cid:1) (cid:1) ((cid:1)) (cid:1) (cid:1) (cid:1) (cid:1) + + (+) + (cid:1) (cid:1) + (cid:1) (cid:1) + (cid:1) (cid:1) 8 K
O
Methanosaetaceae + + (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) + + + + (cid:1) (cid:1) + + + (cid:1) (cid:1) (cid:1) 8 G
A
Methanopyraceae + + (cid:1) (cid:1) + + (cid:1) (cid:1) (cid:1) + + + ? (cid:1) + + + + + (cid:1) (cid:1) 32,33,34 a
n
Thermoplasmataceae + + (cid:1) (cid:1) (cid:1) + + (cid:1) (cid:1) + (cid:1) (cid:1) + (cid:1) (cid:1) + + + + (cid:1) 45,46,47,48 d
H
Thermococcaceae + (cid:1) (cid:1) (cid:1) (cid:1) + ((cid:1)) (+) (cid:1) + (cid:1) (cid:1) + (cid:1) (cid:1) + (cid:1) 15,16,33,82 .
M
Archaeoglobaceae + + (cid:1) (cid:1) + + (cid:1) (cid:1) (cid:1) (cid:1) + + + (cid:1) Tarui,unpublished O
R
Sulfolobaceae + + (cid:1) (cid:1) (cid:1) + + (cid:1) + + + (cid:1) + (cid:1) (cid:1) + + (cid:1) (cid:1) (cid:1) + 5,6,21,22,33 II
Thermoproteaceae + + + + + 83
Thermofilaceae
Desulfurococcaceae (cid:1)
Aeropyrumpernix (cid:1) (cid:1) + (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) (cid:1) (cid:1) (cid:1) + (cid:1) (cid:1) (cid:1) (cid:1) 39
Desulfurococcusmobilis + + (cid:1) (cid:1) + + + 84
Ignicoccusislandicum + + 85
Syaphylothermusmarinus + + 86
Sulfophobococcuszilligii (cid:1) + (cid:1) 87
Pyrodictiaceae + + 88
(+),presentinthetypespeciesofthetypegenusbutabsentinsomeotherspecies
((cid:1)),absentinthetypespeciesofthetypegenusbutpresentinsomeotherspecies
Ar,archaeol;HO,hydroxyarchaeol;C25,C25-chaincontainingarchaeol;Cyc,macrocyclicarchaeol,Usat,unsaturatedarchaeol
CA,caldarchaeol;Ring,cycropentanering-containingcaldarchaeol;H,H-shapedcaldarchaeol;Ctol,calditol
Ino,inositol;Et,ethanolamine;Ser,serine,Gro,glycerol;APT,aminopentanetetrol;Cho,choline
Glc,glucose;Gal,galactose;Man,mannose;GN,(N-acetyl)glucosamine;Gul,gulose;Sul,sulfateorsulfonogroup
NewPolarLipidsfromArchaea 2021
HO CH
A 2
O C H
H C O
2
O CH
H C O 2
H2 C OH
B
O CH
H C O 2
2
O C H
H C O
HOCH
H2 C OH 2
HO CH
2
C
O C H
H2 C O
O CH
H C O 2
H2C OH
D HO CH2
O C H
H C O
2
O CH
HO H C O 2
CH
HO 2
HO O
OH
OH
E H C OH
2
HC O
OCH
2
H C O
2
O CH
HO CH
2
Fig.1. NewTetraether-TypeCoreLipidsfromArchaea.
A, Caldarchaeol; B, isocaldarchaeol;12) and C, H-shaped caldarchaeol from Methanothermus fervidus;14) D, calditoglycerocaldarchaeol;22)
E,crenarchaeol.26)
Fig. 1A by Langworthy,9) and later NMR investigation estimated by respective methods. The parallel isomer
by De Rosa et al. on the tetraether core lipid from was named isocaldarchaeol. ‘‘Caldarchaeol’’, isolated
Caldariella acidophila (later reclassified as Sulfolobus from Thermoplasma acidophilum and Sulfolobus solfa-
solfataricus10)) supported such an arrangement.11) This taricus, is also a mixture of the two isomers. The two
proposal has been tacitly extrapolated to all other isomersmightbeformedbychanceduringhead-to-head
tetraether cores from other archaea. Gra¨ther et al.12) condensation of C20 precursor isoprenoid chains (pos-
found that caldarchaeol isolated from Methanobacteri- siblygeranylgeranylchains)ofadiether-typepolarlipid
um thermoautotrophicum strain Marburg (recently re- precursoroftetraetherpolarlipid.Ifthisisthecase,itis
namedMethanothermobactermarburgensis),apparently possiblethatcaldarchaeolisolatedfromotherarchaeais
homogeneousbythin-layerchromatography(TLC),was a mixture of these isomers.
a mixture of regioisomers with antiparallel (Fig. 1A)
and parallel (Fig. 1B) arrangements of two glycerol H-shaped caldarchaeol from Methanothermus fervi-
moieties based on two independent elaborate degrada- dus and related hyperthermophilic archaea
tion procedures. The principle of one of the reactions is Methanothermus fervidus is a hyperthermophilic
showninFig. 2.Theratioofthetwoisomerswas45:55, methane-producing archaeon isolated from a hot spring
2022 Y.KOGAandH.MORII
backbones bound with C40 isoprenoid diol are glycerol
TsO
OTs OTs andnonitol(orcalditol;hereafterthestructureproposed
O O
O O O O byDeRosaetal.17)iscallednonitol,andthestructureof
OTs O O the natural product and its isomers are called calditol).
1 2 Thestructureofnonitoloriginallyproposedisabranch-
ed open chain nonahydroxynonane (2-(10,20,30-trihy-
droxypropyl)-1,2,3,4,5,6-hexahydroxyhexane, C H O ;
9 20 9
272, Fig. 3A). Nonitol or calditol has a structure in
HO OH which a glycerol moiety is linked to C6 polyol.
Isoprenoid hydrocarbon chains are bound at two
3
hydroxylgroups of the glycerol moiety via ether bonds.
Therefore, nonitol or calditol resembles a glycosylgly-
cerol backbone of glycosyl caldarchaeol. But because
HO O O O
theC6polyolportioncannoteasilyberemovedfromthe
4 5 glycerol moiety, nonitol or calditol is assumed to be a
polyol backbone of the lipid core as a whole, like
Fig.2. DemonstrationofthePresenceofRegioisomersofCaldarch-
glycerol.
aeolandIsocaldarchaeol.
Tosylatedcaldarchaeol1andisocaldarchaeol2weresubmittedto Severalquestionswereraisedbysyntheticstudiesand
theBoordhaloalkoxyeliminationreaction89)(thereactionsitesare instrumental reinvestigation ofthestructure. Jeganathan
shownbyarrows).12)Monoallylether4anddiallylether5aswellas et al.18) synthesized nonitol and found that its NMR
diol 3 were formed, indicating that apparently homogeneous
spectrum was different from that of the natural com-
tetraethercorelipidisamixtureof1and2.
pound. They tentatively concluded that the natural and
syntheticnonitolswerediastereomers.Fairbanksetal.19)
inIcelandthatgrowsfastestat83(cid:2)C.13)Duringanalysis concluded that the structure proposed by De Rosa
ofcorelipidsofM. ferviduscells,Moriietal.14)founda et al.17) was erroneous based on the discrepancies in
new core lipid that migrated more slowly than ordinary NMR spectra between another chemically-synthesized
caldarchaeolonTLC,andhydrocarbonpreparedfromit isomers of nonitol and calditol isolated from Sulfolobus
was not eluted from a column of gas-liquid chromatog- cells,andstatedthatreinvestigationofthestructurewas
raphy(GLC)at350(cid:2)C.Theyassumedthatitmightbea required. Sugai et al.20) questioned the nonitol structure
compoundwithhighmolecularweight.Thisassumption from the mass spectral data (m=z of the molecular ion
was confirmed by MS of the new core lipid and the ½M(cid:1)H(cid:3)(cid:1) ¼253) of calditol isolated from S. acidocal-
derived hydrocarbon. That is, although the molecular darius. They proposed a new structure for calditol,
weightofthecorelipidwas2massunitlessthanthatof shown in Fig. 3B, based on the results obtained by
ordinary caldarchaeol, the molecular weight of the 1H- and 13C-NMR, negative and positive FAB-MS of
hydrocarbon derived from the core lipid coincided with nativeandacetylatedcalditol,andchemicaldegradation
the molecular weight of C80 hydrocarbon. This means analysis. The new structure is an ether of glycerol and
that the new core lipid has a covalent C–C bridge 2-hydroxymethyl-1,2,3,4,5-pentahydroxycyclopentane
between two C40 hydrocarbon chains. Although the (C H O ; 254). Although there should be 32 stereo-
9 18 8
exact location of the bridge has not been established by isomers of calditol due to the five chiral centers on the
MS fragmentation analysis, a most likely structure was ring other than the sn-2 carbon of the glyceryl moiety,
proposed based on data from MS and NMR (Fig. 1C). they went no further than to show that a cis-config-
Moriietal.nameditH-shapedcaldarchaeol.Sugaietal. uration between two proton pairs (H3 and H4) on the
successfullydetectedanH-shapedhydrocarbonbyGLC ring from the results of NOE. Gra¨ther et al.21) inde-
at a higher temperature from the lipid of Pyrococcus pendently proposed a different isomeric structure
horikoshii15)andafurther3speciesoutof16speciesof (Fig. 3D) for the calditol structure based mainly on
the family Thermococcaceae.16) This result indicates NMR studies. Finally, Ble´riot et al.22) synthesized four
that the occurrence of H-shaped caldarchaeol is not stereoisomersofcalditolaroundthechiralcentersofC-2
family-specific. It was confirmed that H-shaped cal- and C-3 on the ring, and one of them (Fig. 3D) was
darchaeol is, in fact, a core portion of polar lipids by found to be fully identical to the natural product in 1H
preparing it from a polar lipid fraction, although the and 13C-NMR and optical rotation. All three proposals
complete structure of a polar lipid with H-shaped for the calditol structure are consistent in the planar
caldarchaeol core is not known. structure in which 2-hydroxymethyl-1,2,3,4,5-penta-
hydroxycyclopentane is linked via an ether bond with
Correct structure of calditol in Sulfolobus spp. the glycerol moiety at the sn-1 position. The difference
De Rosa et al.17) reported that two kinds of tetraether among the three proposals is the configuration around
core lipids were found in Sulfolobus solfataricus, the five chiral centers on the cyclopentane ring. Ble´riot
ordinary diglycerocaldarchaeol (Fig. 1A) and glycero- etal.depictedthecalditolstructureproposedbySugaiin
nonitocaldarchaeol. In the latter core lipid, two polyol their paper as structure 5 (Fig. 3C). This is in fact an
NewPolarLipidsfromArchaea 2023
CH OH
CH OH 2
2 OH
CH2OH H C OH H C OH
H C OH CH CH2 OH OH
HC OH O 2 OH O OH O OH
H H H OH
H2OCH OCH OCH OCH OCH OCHH2 1 OH 5 3 4OH OH OH OH HO CCH2H
2
OH CH OH
HO OH 2
A De Rosa B Sugai C 5 D Gräther, Bleriot
CH2OH CH2OH CH2OH
H C OH H C OH H C OH
CH2 CH2 CH2
1 O O O
2
OH HO HO
OH OH OH
5 OH HO HO
HO 3 OH OH
HO 4 OH OH
E F G
Fig.3. ProposedStructuresofNonitolandCalditol.
A,Open-branchedchainstructureproposedbyDeRosa.17)BandE,ProposedbySugaietal.20)CandF,Structure5depictedinBle´riot’s
paper22)astheSugai’sproposal.DandG,Correctstructureofcalditol,proposedbyGra¨ther21)andBle´riotetal.22)
diastereomerofSugai’scalditol.AsshowninFig. 3E,F, from a polar lipid fraction, C40 isoprenoid hydrocarbon
the ring configurations are in mirror images, while the with three cyclopentane rings at unusual position in
glycerolmoietiesofthetwostructuresareabsolutelythe particulate and sedimentary organic matter samples of
same. Ble´riot’s caldtitol structure is different from water column from several marine environments
Sugai’s in the configuration at the four positions of the (Fig. 4A).Thesame unusualcyclopentaneringcontain-
ring, not at a single stereocenter as they mentioned. ing biphytane C40 3Ri was also detected in picoplank-
Structure 5 (in the Ble´riot’s paper) is, therefore, ton collected from sea water in Antarctica.24) Because
unfounded. The correct structure of calditol has been these hydrocarbons were prepared by HI-LiAlH treat-
4
elucidated to be the structure shown in Fig. 3D (= G). ment of the extracted samples, they were probably
The structure of calditol-containing caldarchaeol (caldi- present as an ether lipid form in the samples. rRNA
toglycerocaldarchaeol) is shown in Fig. 1D. According analysis of the same sample revealed that they were
to Sugai et al., the intramolecular ether linkage is nonthermophilic crenarchaeotes. Hoefs et al. discussed
resistant to BCl treatment, probably due to steric the fact that planktonic archaea have thrived in marine
3
hindrance,butitcanbecleavedbyheatingwith57%HI environments for at least the past 50 million years
at 100(cid:2)C for 60h. judging by the occurrence of the characteristic lipids in
the fossil record.23) Schouten et al.25) found a variety of
Crenarchaeol and archaea-related lipids in environ- tetraether core lipids with isoprenoid-derived and non-
ment samples isoprenoid branched hydrocarbons from various envi-
AnalysesofrRNA andcaldarchaeol oritscomponent ronmental samples by use of the HPLC/MS technique.
C40 isoprenoid are two main markers to detect the Among them, novel and unique structures were found.
presence of archaea in environmental samples, espe- For example, a C31 chain with three methyl branches
cially marine picoplanktons and sediments. In addition (Fig. 4B), a C30 chain with one methyl branch and one
to ordinary C40 biphytane (C40 H–H), various new cyclopentanering(Fig. 4C),andC35andC37chainsin
hydrocarbons have been found. Hoefs et al.23) detected, which a C20 isoprenoid chain and an C15 and C17 iso-
2024 Y.KOGAandH.MORII
Allyl ether type core lipids from Methanopyrus
A
kandleri and Methanococcoides burtonii
Methanopyrus kandleri is another hyperthermophilic
methanogenic archaeon, whose optimal growth temper-
ature is 98(cid:2)C.29) The organism is phylogenetically the
B
most distantly related with other methanoarchaea.30)
Digeranylgeranylglycerol (unsaturated archaeol) was
first discovered by Hafenbradl et al.31,32) in the non-
polar lipid fraction of Methanopyrus kandleri. They
C
reported in the same paper,32) however, that the core
lipidpreparedbyHCl-methanolysisofpolarlipidsofthe
organismwascomposedonly ofsaturated archaeol.But
D Sprott et al.33) have shown the presence of unsaturated
archaeol-based phospholipids, the most abundant of
which is unsaturated archaetidylcholine, in the same
archaeon by MS of total lipids. Nishihara et al.34)
O reexamined HCl-methanolysis for choline-containing
E
phospholipids, and they found that most of the phos-
pholipids were degraded during methanolysis but that a
O small amount of the lipid remained intact, composed of
saturatedarchaeolasacore.Theyassumedthattheacid-
OH degradedportionofthe phospholipidswascomposed of
acid-labile allyl ether core lipids. To confirm this
Fig.4. Archaea-Related and Non-Archaeal Hydrocarbons from En- assumption, they developed a LiAlH reductive cleav-
4
vironmentalSamples. age method of allyl ether bonds.34) Allyl ether-bonded
A, C40 isoprenoid with three cyclopentane rings at an unusual
hydrocarbonwasreleasedasintacthydrocarbonbytheir
position;23) B, C31 non-isoprenoid hydrocarbon with three methyl
method. The products were identified as unsaturated
branches;25) C, C30 non-isoprenoid hydrocarbon with a cyclo-
pentane ring;25) D, C35 hybrid hydrocarbon apparently formed by isoprenoid hydrocarbons with one, two, three, or four
combination of C20 isoprenoid and iso-branched C15 non-isopre- double bonds by GLC–MS. In this way acid-labile
noid hydrocarbon;25) E, cyclic archaeol with two cylopentane phospholipid with allyl ether-bonded hydrocarbons was
rings.28)
first chemically characterized (Fig. 5). LiAlH does not
4
attack saturated ether, alk-10-enyl ether (plasmalogen),
or reduce an ethylene double bond, but cleaves an ester
branched fatty chain, respectively, are conjugated bond or a phosphodiester bond.35)
(Fig. 4D), are especially unique. A cyclohexane ring- The hydrocarbon was proportionally released from
containing lipid (Fig. 1E) added a new member to the the original allyl ether lipid by this method even if
ring-containinglipidfamily.Theoriginaltetraetherlipid absolute recovery was not achieved. Quantitation of
containing a cyclohexane ring was named crenarch- allyl ether-bonded hydrocarbon by GLC, therefore, was
aeol.26) Mono- or di-methyl branched hydrocarbons achieved by measuring the ratio of the sample to an
might be derived not from archaea but from thermo- internal standard (n-tetracosane), which gave a hydro-
philic bacterial members, such as Thermotoga, which carboncompositionofarchaetidylcholineoftotalallylic
contains 15,16-dimethyl-30-glyceryloxitriacontanoic hydrocarbon of 78%, non-allylic unsaturated hydro-
acid.27) Two latter conjugated hydrocarbons can be carbon of 16%, and saturate hydrocarbon of 6%. Of the
regarded as hybrid lipids between archaeal isoprenoid allylic hydrocarbon, the composition was four double
lipidsandbacterialfattychains.Itisnotknownwhether bond-species, 47%; three double bond-species, 11%;
the hybrid lipids occurred in an assumed hybrid two double bond-species, 14%; and one double bond-
organism or were formed abiotically in an environment species, 7%. On the basis of the acid lability of allyl
after the death of the parent organisms. It may be ether lipids, the molecular species of archaetidylcholine
expected that new archaeal organisms will be isolated were estimated by phosphate determination of HCl-
and proved to contain these new lipids in their cells. degradation products of archaetidylcholine (see Ref. 36
Stadnitskaia et al.28) identified a new macrocyclic forthemethod).Theresultswerealmostconsistentwith
archaeol with one or two cyclopentane rings in the thehydrocarboncompositiondescribedasabove.34)This
biphytanediyl chain (Fig. 4E) in carbonate crust taken wasthefirstexampleofestimationofmolecularspecies
from the Black Sea. This new compound resembles composition of archaeal ether phospholipid. In addition
cyclic archaeol without a cyclopentane ring of Meth- to archaetidylcholine, six phospholipids, including
anocaldococcus jannaschii on the one hand, and also phosphorylated N-acetylglucosaminyl archaeol, archae-
resembles cyclopentane ring-containing caldarchaeol in tidylinositol, hydroxyarchaetidylserine, hydroxyarchae-
Sulfolobus spp. on the other. tidylethanolamine or unsaturated archaetidylglycerol,
NewPolarLipidsfromArchaea 2025
HCO HCO
2 2
HCO HCO
O O
H C O P O CHCHN+(CH) H C O P O CHCHN+(CH)
2 2 2 33 2 2 2 33
O- O-
HCO
2 HCO
2
HCO
HCO
O
O
H C O P O CHCHN+(CH)
2 2 2 33 H C O P O CHCHN+(CH)
O- 2 2 2 33
O-
HCO
2
HCO
O
H C O P O CHCHN+(CH)
2 2 2 33
O-
Fig.5. SomeoftheMolecularSpeciesofArchaetidylcholinefromMethanopyruskandleriwithDifferentNumberofDoubleBonds.
Topfourstructuresshownareallyetherlipids.34)
unsaturated archaetidylethanolamine, and archaetidyl- Longchainarchaetidyl-myo-inositolandarchaetidyl-
ethanolamine,sixarchaeol-basedglycolipidswithoneto glucosyl-myo-inositol from Aeropyrum pernix
six hexose units, and one tetraether type phosphoglyco- Aeropyrum pernix was the first absolutely aerobic,
lipid, dihexosyl caldarchaetidylglycerol, have been hyperthermophilic archaeon isolated at a coastal solfa-
identified, mainly by FAB-MS.33) Total lipid of taric thermal vent in Kodakara-Jima island in Japan. It
M. kandleri is rich in non-polar lipid (the polar lipid grows optimally at 90–95(cid:2)C.38) Total polar lipid is
fraction represents only 50% of the total lipids), and composedoftwomajorphospholipids,archaetidyl-myo-
more than 92% of the polar lipids are glycolipids.32) Of inositol and archaetidyl-(glucosyl)-myo-inositol,39) in
the four kinds of glycolipid-sugar, mannose is predom- addition to one minor phosphoglycolipid and two
inant (86%). Such membrane lipid composition appears glycolipids.38)Each ofthemajor phospholipidscontains
to be unique compared with that of other microorgan- only one kind of core lipid with two C25 isoprenoid
isms. chains. Although an archaeol core lipid with two C25
Nichols et al.37) have also identified unsaturated isoprenoid chains had been found in haloalkaliphilic
archaeol- and unsaturated hydroxyarchaeol-based phos- Archaea,40) it also contains a C20 chain. It is the first
pholipidswithglycerolandinositolaspolarheadgroups example that all isoprenoid chains in polar lipids are
by HPLC–MS in a psychrotrophic methanoarchaeon, C25 isoprenoid without a C20 chain in the cells of one
Methanococcoides burtonii, isolated at Ace Lake in species of archaeal organism. Archaetidyl-myo-inositol
Antarctica. They reported that the unsaturated archaeol isnotverynovelalipidexceptforthelongerisoprenoid
core contains one to five double bonds, although the chains. Archaetidyl-(glucosyl)-myo-inositol, however,
location of the double bonds could not be determined. hasauniquestructure,inwhich an(cid:1)-D-glucosylmoiety
They also described that the unsaturated hydroxyarch- is bound at the 2 position of myo-inositol of archaeti-
aeol core lipid contained one to four double bonds. dylinositol (Fig. 6). Archaetidyl-(glucosyl)-inositol
These unsaturated ether phospholipids are all new ones. resembles archaetidyl-(glucosaminyl)-myo-inositol in
Although they depicted the structural formula of (cid:1)- Methanosarcina barkeri, but is different in the glycosyl
hydroxyarchaetidylglycerol and (cid:1)-hydroxyarchaetidyli- moietyandinthepositionofinositolatwhichglycoside
nositol in their paper, no evidence for the (cid:1)-isomer of is linked.
hydroxyarchaeol was presented. Koga et al.8) have
reported the presence of (cid:2)-hydroxyarchaeol in the same II. New Ether Polar Lipids
organism based on lipid component parts analysis.
Hydroxyarchaetidylglycerolandhydroxyarchaetidylino- (cid:2)-hydroxyarchaetidylethanolamine and (cid:2)-hydroxy-
sitol in M. burtonii, therefore, are most likely (cid:2)- archaetidylglycerol from Methanosarcina barkeri
hydroxyarchaetidylglycerol and (cid:2)-hydroxyarchaetidyli- TotallipidofMethanosarcinabarkeriiscomposedof
nositol. nine major phospholipids with archaeol or (cid:2)-hydroxy-
archaeolasacorelipid.Fourkindsofpolarheadgroups,
2026 Y.KOGAandH.MORII
H C O
2
H C O
O
O P O CH
H C OH 2
2
O O-
O
Fig.6. Archaetidyl-(glucosyl)-myo-inositolfromAeropyrumpernix.39)
Halobacterium salinarum. The purple membrane of a
H2CO Halobacterium cell contains only one protein, bacterio-
A OH rhodopsin, a photo-driven energy-transducing protein,
HC O
O associated with special lipids. The phospholipid is an
HNCH CH O P O CH
2 2 2 2 ether analog of cardiolipin (Fig. 8A), and the phospho-
OH
glycolipid is archaetidylated S-TGA-142) (Fig. 8B). An
ether analog of cardiolipin is bisarchaetidylglycerol. By
thisfinding,ether-typeanalogsofallkindsofbacterial/
H CO
2
B eukariotic ester phospholipids (ethanolamine-, serine-,
OH
HC O glycerol-, myo-inositol-, choline-phospholipids, and
O
cardiolipin) have been found in archaeal phospholipids,
H2C OP O CH2
OH except for monomethyl- and dimethyl-ethanolamine-
H C OH phospholipids. S-TGA-1 is a major glycolipid of halo-
HC OH bacteria, the structure of which is sulfogalactosyl-
2
mannosyl-glucosyl archaeol. An additional archaetidyl
Fig.7. NewPolarLipidsfromMethanosarcinabarkeri.39) group is bound at position 6 of the glucosyl moiety of
A, (cid:2)-hydroxyarchaetidylethanolamine; B, (cid:2)-hydroxyarchaetidyl-
S-TGA-1inthenewlipid.Itisinterestingthatthesenew
glycerol.
lipids have four phytanyl chains in their molecules.
Corcelli et al.42) discussed the possible role of these
L-serine, myo-inositol, ethanolamine, and glycerol, are lipidsintheenergy-transducingapparatus,asineukary-
attached to archaeol and (cid:2)-hydroxyarchaeol through a otic mitochondria. The ether analog of cardiolipin and
phosphodiester bond (eight phospholipids). Another another phosphoglycolipid which has archaetidylated
one is archaetidyl-(glucosaminyl)-myo-inositol. No (cid:2)- 6-sulfomannosyl-glucosyl archaeol (archaetidylated
hydroxyarchaeol derivative of the last one was found. S-DGA-1) have also been identified from cells of
Among these nine lipids, seven phospholipids were Haloferax volcanii, which lacks purple membranes43)
reviewed in a previous paper.7) (cid:2)-hydroxyarchaetidyl- (Fig. 8C).
ethanolamine and (cid:2)-hydroxyarchaetidylglycerol were
newly reported41) (Fig. 7A, B). Cells of the genus Polar lipids from Thermoplasma acidophilum
Methanosarcina contain little glycolipid compared with The main polar lipid (MPL) of Thermoplasma acido-
other methanogens. Hydroxyarchaeol core and myo- philum was characterized incompletely as glycosyl
inositol, ethanolamine, and glycerol as phosphodiester- caldarchaetidylglycerol.44) In 1997, Swain et al. identi-
linked polar groups are the common markers of fied (cid:2)-L-gulose as the sugar moiety of the MPL by MS,
members of the family Methanosarcinaceae. This NMR, GLC–MS of acetylated butyl glycoside, and
conclusion was derived from analysis of the lipid optical rotation data.45) Thus the MPL was identified as
component parts of 13 strains from 10 species of the (cid:2)-L-gulosylcaldarchaetidylglycerol. Gulose and an L-
family.8) form sugar are rare in nature, but a few examples in
bacteria and eukaryotes are cited in Swain’s paper.45)
Ether analog of cardiolipin (bisarchaetidylglycerol) Hydroxyarchaetidylglycerolandhydroxyarchaetidylino-
and two phosphosulfoglycolipids from extreme halo- sitol were detected by MS of roughly fractionated polar
philes lipid as minor phospholipids in the same organism.45)
Although halobacterial lipids had been extensively This was the first report of the occurrence of hydroxy-
studied, mainly by Kates group,6) a new phospholipid latedphospholipidsinotherthanmethanogenicarchaea.
and a new phosphoglycolipid have been identified from Itisnotknownwhetherthehydroxyarchaeol isan(cid:1)-or
purple membrane of a genetically engineered strain of (cid:2)-isomer. Becausethepolarhead group ofThermoplas-
NewPolarLipidsfromArchaea 2027
H C O
2
A HC O
O
H C O P O CH
2 2
OH
HC OH
O
H C O P O CH
2 2
OH
HC O
H C O
2
B
H C O
2
Archaetidyl group HC O
OHCH
2
O P O
CH2OH O H2C O
O CH
O 2
S-TGA-1 O O HC O
CH
2
HSO3 O O CH2
O
H C O
2
C
HC O
OHCH
2
O P O
O
O
H C O
2
CH
2
S-DGA-1 O HC O
HSO CH
3 2
O O CH
2
O
Fig.8. NewLipidsfromExtremelyHalophylicArchaea.
A, ether-type analog of cardiolipin, viz., bisarchaetidylglycerol;42) B, archaetidylated S-TGA-1, viz., 300-sulfoGalp-(cid:2)100,60Manp-(cid:1)10,2-
(6-archaetidyl)-Glcp-(cid:1)1-archaeol;42)C,archaetidylatedS-DGA-1,viz.,60-sulfoManp-(cid:1)10,2-(6-archaetidyl)-Glcp-(cid:1)1-archaeol.43)
ma lipids had been thought to be only glycerol, inositol colipid, GPL-K, which is (cid:1)-D-glucosyl caldarchaetidyl-
asthepolarheadgroupofThermoplasmalipidsisanew glycerol. This is an isomer of GPL-A (MPL or gulosyl
finding. Gulosyl caldarchaetidylglycerol was also pres- caldarchaetidylglycerol). In this archaeon, it is interest-
ent in another species of the genus Thermoplasma ingthatL-guloseisina(cid:2)-anomerandD-glucoseinan(cid:1)-
(T. volcanium).45) anomer. It should be noted that the orientations of the
Uda et al.46,47) identified six minor glycolipids in hydroxylgroupatthe1positionandthehydrogenatthe
T. acidophilum. Although most tetraether type bipolar 5positionofsugarswithD-(cid:1)-andL-(cid:2)-configurationsare
lipids carry glycosyl groups inone end and aphosphate the same. Shimada et al.48) comprehensively analyzed
ester at another end, they found unusual glycolipids in thestructuresof13polarlipidsseparatedbyHPLCwith
which glycosyl groups are bound at both ends of anevaporativelight-scatteringdetecter.Ofthe13lipids,
caldarchaeol.Thesugarmoietiesboundatthebothends 7hadnotbeenpreviouslyreported.Allthesenewlipids
of caldarchaeol are gulose/gulose (GL-2a), gulose/ are composed of a caldarchaeol core, one or two gulose
glucose (GL-2b), and glucose/glucose (GL-2c). The and one to three mannose as sugar moieties, and
other two lipids are gulosyl caldarchaeol and glucosyl phosphoglycerol asa phosphodiester-linked polargroup
caldarchaeol. They also identified a minor phosphogly- insomephosphoglycolipids.Inaddition,asmallamount
2028 Y.KOGAandH.MORII
ofdiether-typearchaetidylglycerolwas detected.Ferro- III. Taxonomic and Ecological (environmen-
plasma acidiphilum, a mesophilic relative to T. acid- tal) Aspects
ophilum, produced (cid:2)-D-glucopyranosyl caldarchaetidyl-
glycerol,49) the anomer of T. acidophilum minor lipid Ether lipids as a chemotaxonomic marker
(GPL-K) found by Uda et al.47) The taxonomic significance of the polar lipid compo-
sition of archaea was suggested as early as the mid
Polar lipids of Methanothermus fervidus, Pyrococcus 1980sformethanogenic51,52)andextremelyhalophilic53)
furiosus, and Sulfolobus acidocaldarius archaea. This was based on comparisons of TLC
Sprottetal.33)reportedpolarlipidconstituentsinfour patterns of total polar lipid of each archaeon. Koga et
hyperthermophilic archaea mainly using negative-ion al.54) developed lipid component parts analysis for
FAB-MS. They identified the following polar lipids in taxonomical purposes to incorporate more structural
M. fervidus total lipids by FAB-MS: acetyl-di-hexosyl informationonlipidsmaintainingalesstime-consuming
caldarchaetidylinositol, di-hexosyl caldarchaetidylino- simplicity.Themethodhasbeendiscussedinaprevious
sitol, acetylhexosyl caldarchaetidylinositol, hexosyl cal- review.7) Koga et al. confirmed the effectiveness of the
darchaetidylinositol,caldarchaetidylinositol,caldarchae- method and showed the correlation of polar lipid
tidic acid, acetyl-di-hexosyl archaeol, di-hexosyl composition with 16S rRNA phylogeny in methano-
archaeol, phosphorylated N-acetylhexosyl archaeol, gens.8) The latest version of Bergey’s Manual of
archaetidylinositol, hexosyl archaeol, archaetidyleth- Systematic Bacteriology55) incorporated much lipid
anolamine, and archaetidylglycerol, of which the phos- information in the description of each taxon. Lipid
phoglycolipids with acetylated sugar were new lipids. componentpartsanalysiswasappliedtoidentificationof
Removal and analysis of polar groups showed the a few newly isolated methanogens.56,57)
presence of glucose, N-acetylglucosamine, and inositol.
In P. furiosus, dihexosylcaldarchaetidylinositol, di- Ether lipids in environmental research
hexosylcaldarchaetidylglycerol, monohexosylcaldarch- Lipid analysis of environmental samples yielded one
aetidylinositol, caldarchaetidylinositol, dihexosylarch- of the base of the hypothesis of possible anaerobic
aeol, phosphorylated acetylhexosylarchaeol, arch- methane oxidizing archaea. Hinrichs et al.58) found
aetidylinositol or phosphorylated hexosylarchaeol, and archaeoland(cid:2)-hydroxyarchaeolinlipidsextractedfrom
archaetidylglycerolwereidentifiedasthemostprobable marine sediment samples taken from methane seepage
structures from m=z of their molecular ions. Identifica- (inoffshorenorthernCalifornia).Thesearchaea-specific
tion of individual lipids with only FAB-MS data of lipid biomarkers were extremely depleted in 13C.
unfractionated total lipid is accompanied by certain Because biologically produced methane is highly de-
ambiguities;viz.,archaetidylinositolandphosphorylated pletedin13C,itwasassumedthatthe13C-depletedlipids
hexosylarchaeol cannot be distinguished, kinds of are produced by new archaea that anaerobically metab-
hexose cannot be determined, structural and stereo- olize 13C-depleted methane. A parallel gene survey of
chemical isomers cannot be distinguished, and it is not 16S rRNA indicated the predominance of new archaeal
possible to distinguish whether a m=z signal represents groups thatareperipherally related tothe methanogenic
an intact molecule of a lipid or a fragmentation product orders Methanomicrobiales and Methanosarcinales.
of a lipid of higher mass. Nevertheless, FAB-MS was a These genes were not found in control sediment
useful method to detect individual lipids in total lipid samples. Because hydroxyarchaeol is found predom-
extractedfromarchaealcellswithoutpurification,andit inantlyinorganismsoftheorderMethanosarcinales,the
should, therefore, be of use for ecological or environ- results of the analysis of lipid biomarkers and those of
mental analysis or taxonomic purposes. For determina- 16S rRNA phylogenetic analysis are consistent. It was
tion of complete structure, other instrumental and shown by the fluorescent in situ hybridization (FISH)
chemical methods must be combined. method that cells of one of the Methanosarcinales-
By the same methods, diether polar lipids of Sulfo- related groups of archaea (ANME-2) were present,
lobus acidocaldarius were identified: dihexosyl archae- forming close consortia with sulfate-reducing bacte-
ol, hydroxyarchaetidylinositol, archaetidylinositol, hy- ria.59)Althoughnomethane-oxidizinganaerobicarchaea
droxyarchaetidylglycerol, archaetidylglycerol, and has been isolated, anaerobic methane oxidation is
archaetidylethanolamine. These lipids were similar to thought to be a globally significant process of the
the lipids found in Methanosarcina barkeri. Hydroxy- carbon cycle and to contribute greatly to reduce green-
archaeol as a core and glycerol and ethanolamine as house gas flow from the ocean. Lipid analysis made an
phosphodiester-linked polar head groups were first important contribution in elucidating the microorgan-
foundinSulfolobussp.Itisexpectedthattheoccurrence isms involved in this significant process.
ofthese lipids will be confirmed byapplication ofother In the ecological application of archaea-specific lipid
methods to the isolated lipids. Sugai et al. identified a analysis, large progress was made by identification of a
new major neutral glycolipid (GL-1a) as (cid:2)-glucosylcal- varietyofnewhydrocarbonsderivedfromarchaealcore
ditoglycerocaldarchaeol with two or three cyclopentane lipids or core lipids themselves, as described in the
rings on the hydrocarbon chains.50) previous section. These findings strongly suggest new