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Escherichia coli and Bacillus subtilis: The Frontiers of Molecular Microbiology Revisited, 2012: 341-355
ISBN: 978-81-308-0492-7 Editors: Yoshito Sadaie and Kouji Matsumoto
11. Archaea and Bacteria
11-1. Role of membrane lipids in the first specific
differentiation
Yosuke Koga
9-14-20 Hinosato, Munakata 811-3425 Japan
1. Abstract. All the living organisms are classified into three
domains (the newly proposed highest rank of classification of
organisms). Escherichia coli and Bacillus subtilis are belonging to
one of the domains, Bacteria. Works on the two bacteria made a
great deal of contribution to construct modern microbiology, new
concept of biochemistry and molecular biology. Compared with
research history on Bacteria, Archaea have been studied merely in
these three decades, however, the uniformity and diversity in
biochemical properties of Archaea seem to illustrate pre-existing
knowledge of Bacteria from the back, that is, bacterial information
that had been ignored was discovered as novel aspects of
biochemistry and molecular biology. One of them is the “lipid
divide”, that is, the difference of stereo structure of glycerophosphate
of membrane lipid backbone and hydrocarbon chains. In this chapter,
first, a quite unique structure and biosynthesis of archaeal membrane
lipids are introduced and then a hypothesis on the differentiation of
Archaea and Bacteria mainly driven by segregation of
glycerophosphate enantiomers of lipid backbones and hydrocarbon
chains in the universal common ancestor.
Correspondence/Reprint request: Dr. Yosuke Koga, 9-14-20 Hinosato, Munakata 811-3425 Japan
E-mail: [email protected]
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Yosuke Koga
2. Arachaea and bacteria: Two descendants of the universal
common ancestor
Escherichia coli and Bacillus subtilis are classified in Bacteria, which is
a domain of life newly proposed phylogenetic classification of all life [1].
Other domains are Archaea and Eukarya. Because cells of Eukarya are
generally accepted as cells emerged by symbiosis of an ancient archaeal and a
bacterial species, Archaea and Bacteria are two fundamental lineages of life.
Microbiological knowledge has been accumulated mainly on the basis of
researches on many species of Bacteria, because researches on Archaea have
only far young history compared with that of Bacteria. However, recent
rapidly growing archaeal studies revealed novel aspects of insight of history
of life. Experimental results on Archaea accumulated during these several
decades showed significant differences from and fundamental similarities to
Bacteria in biochemical and molecular biological aspects.
Significant differences between biochemical and molecular biological
aspects in Archaea and Bacteria have been stressed. In fact, archaeal
characteristics are very striking. However, it should be recalled that Archaea and
Bacteria have fundamentally common chemistry of cellular constituents and
biochemical mechanisms. Both lineages of organisms share DNA, RNA, protein,
sugars, and glycerolipids that are identical in fundamental structures. Types of
bases and pentoses of DNA or RNA, amino acids, primary hexoses, ATP, and
coenzymes are common. Among biochemical mechanisms, membrane lipids
show maximum difference in structure (see below). Though Archaea and
Bacteria show diverse biosynthetic and energy-yielding metabolisms,
fundamental uniformity can be seen such as glycolysis, gluconeogenesis, TCA
cycle, DNA replication, transcription, translation, and chemiosmotic mechanism
of ATP synthesis. The unity and diversity of chemistry and biochemistry in
Archaea and Bacteria are certain evidence for the existence of a common
ancestor of Archaea and Bacteria. That is, Archaea and Bacteria, which are
basically fundamental lineages of life, were differentiated from one common
ancestor. Comparison of biochemical features in Archaea and Bacteria may result
in suggestion of the mechanism of differentiation.
Although phylogenetic difference between Archaea and Bacteria is
observed by comparison of base sequences of rRNA, this is merely difference
in base sequence in the polymers that has been accumulated during their
evolutionary history from a common ancestral molecule but not from
different compounds. The most different compounds in the both domains of
organisms that fulfill common function are membrane lipids. Correct insight
of the difference between archaeal and bacterial membrane lipids could lead
Early evolution of lipids
343
one to understand essence of two significant lineages of life on the Earth.
Therefore, this chapter starts with a brief review of archaeal lipids.
3. Structure and biosynthesis of archaeal membrane lipids
Basic structure of polar lipids in Archaea
Archaeal polar lipids are composed of sn-glycerol-1-phosphate as a
backbone and two isoprenoid chains (usually C20 phytanyl group) bound at
the sn-2 and 3 positions (see footnote 1) of the backbone (archaetidic acid). A
polar group (such as myo-inositol, glycerol, or serine/ethanolamine) is linked
to the free hydroxyl group of phosphate group to form a phosphodiester
bonds (archaetidyl-X, where X is, for example, myo-inositol). Glycolipids
have two or more hexose units at the sn-1-position where a phosphatecontaining polar group is removed (2, 3-di-phytanyl-sn-glycerol is called
archaeol). Two polar lipids are often coupled by head-to-head condensation
at the methyl termini of phytanyl groups to give rise to a tetraether polar lipid
with two glycerol units, two C40 biphytanediyl chains, and a phosphatecontaining polar group and an oligoglycosyl group. A tetraether lipid derived
from this type of polar tetraether lipid by removing both polar groups is
caldarchaeol. Archaeol and caldarchaeol are core lipids (Fig. 1) [2,3].
Figure 1. Characteristics of archaeal membrane lipids. 1) The stereochemistry of
glycerophosphate backbone is sn-glycerol-1-phosphate. 2) Ether bonds between
isoprenoid chains and G-1-P backbone. 3) Isoprenoid hydrocarbon chains (mostly
C20 phytanyl group). The bacterial counterparts are sn-glycerol-3-phosphate, ester
bonds, and fatty acyl chains, respectively.
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Yosuke Koga
The most critical distinction between archaeal and bacterial membrane
lipids is stereo chemical difference in the glycerophosphate (GP) backbones
of the phospholipids. This is called the “lipid divide”. Although there are
exceptions in the type of hydrocarbon chains and ether/ester bonds, there is
no exception reported for the stereochemistry of GP to date. Thus, the “lipid
divide” may account for the fundamental difference in membrane lipids
between Archaea and Bacteria.
Varieties of archaeal polar lipids
There are a wide variety of diether- and tetraether-types of core lipids
and polar head groups. Well-known structural varieties of archaeal lipids are
shown in Fig. 2.
One species of archaeon possesses one to several kinds of core lipids and
two or more polar head groups. Consequently, combination of various core
lipids and polar groups give rise to tens of polar lipid species in one species
of archaeon. Composition of polar lipids of an archaeal species is roughly
related with phylogenetic relationship [4].
Figure 2A
Early evolution of lipids
345
Figure 2B
Figure 2. Variation of core lipids in Archaea. A, archaeol analogs; and B,
caldarchaeol analogs.
Biosynthetic pathway of archaeal polar lipids
Isoprenoid chains in archaeal polar lipids are synthesized by the wellknown mevalonate pathway, which is slightly modified, in contrast with the
1-deoxy-D-xylulose-5-phosphate (DOXP) pathway found in most bacterial
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Yosuke Koga
species (for details, see ref. 5). The most significant feature of archaeal
phospholipid biosynthetic mechanism is the formation of the enantiomeric
backbone
structure
of
G-1-P,
which
is
formed
from
dihydroxyacetonephosphate (DHAP) by G-1-P dehydrogenase [6]. Because
phosphorylation of glycerol forms G-3-P but not G-1-P, this reaction does not
involve in G-1-P formation. By contrast, G-3-P backbone of bacterial
phospholipids is formed from DHAP by G-3-P dehydrogenase or by
phosphorylation of glycerol by glycerol kinase. The G-1-P dehydrogenase
activity was detected in the cell homogenates of all the Archaea so far
measured and the gene coding the enzyme was detected in all the Archaea of
which whole genome sequence was published.
Archaeal lipid biosynthesis (Fig. 3) starts with etherification at the
positions of sn-2 and 3 with geranylgeranyl diphosphate. The first and second
products are geranylgeranyl-G-1-P (GGGP) and digeranylgeranyl-G-1-P
(DGGGP, unsaturated archaetidic acid), respectively. Archaetidic acid is
reacted with CTP to form CDP-archaeol, which is an activated form of
archaeol. This reaction mode is identical to bacterial phospholipid synthesis
(CDP-diacylglycerol formation). CDP-archaeol is a central intermediate for
the phospholipid biosynthesis, because it reacts with most polar head groups
to form phospholipids with the corresponding polar group by replacing CMP
moiety of CDP-archaeol.
CDP-archaeol synthase uses specifically unsaturated archaetidic acid
with geranylgeranyl chains as isoprenoid chains, while archaetidylserine
synthase and archaetidylinositol phosphate synthase react with saturated or
unsaturated CDP-archaeol with phytanyl or geranylgeranyl chains. An
enzyme that reduces double bonds of geranylgeranyl chains bound in
phospholipids is found in Archaea [7]. Because the substrate specificity of
the enzyme is not so tight, the exact point of reduction (saturation) of
unsaturated isoprenoid chains is not clear. Most archaeal polar lipids as end
products have saturated isoprenoid chains.
Major polar head groups in archaeal phospholipids are synthesized in
cytoplasmic compartment of archaeal cells by soluble enzymes from the
intermediates of glycolysis or gluconeogenesis. L-serine was synthesized
from phosphoenolpyruvate, GP is formed directly from DHAP, and myoinositol-1-phosphate is from D-glucose-6-phosphate.
Enzymes for lipid biosynthesis
Although little enzymes of lipid biosynthesis in Archaea have been
purified, some properties of the enzymes were reported. Characteristics
relevant with lipid-driven differentiation of Archaea and Bacteria are briefly
described below.
Early evolution of lipids
347
Figure 3. Biosynthetic pathway of archaeal membrane lipids (archaetidylserine [AS],
archaetidylinositol [AI], and diglucosylarchaeol (DGA)). The mevalonate pathway by
which geranylgeranyl diphosphate is synthesized from acetyl-CoA is partly abridged.
DHAP, dihydroxyacetonephosphate; GAP, glyceraldehyde-3-phosphate; DMAPP,
dimethylallylphosphate; PPi, pyrophosphoric acid.
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Yosuke Koga
G-1-P-dehydrogenase
Part of characteristics of synthetic enzymes of lipids in Archaea is
relevant with consideration of differentiation of Archaea and Bacteria.
Because G-1-P dehydrogenase has little amino acid sequence similarity with
G-3-P dehydrogenase, the stereo specificity of G-1-P dehydrogenase and
G-3-P dehydrogenase could not be interchangeable [8]. That is, the two
enzymes are derived from different ancestral enzymes. G-1-P dehydrogenase
is a member of an enzyme family including glycerol dehydrogenase, alcohol
dehydrogenase and dehydroquinate synthase. G-1-P dehydrogenase
specifically transfers pro-R hydrogen of NADH to reduce DHAP to form
G-1-P, in contrast to G-3-P dehydrogenase, which transfers pro-S hydrogen
of NADH. The two dehydrogenases would have symmetric 3D structures at
least from the point of view of nicotinamide plane.
Ether bond forming enzymes
The first ether bond-forming enzyme (GGGP synthase) is specific to G1-P. G-1-P dehydrogenase provides G-1-P and GGGP synthase determines
the final stereochemistry of archaeal polar lipids by its substrate specificity.
Because the enzymes hereafter in the lipid synthetic pathway of Archaea are
not G-1-P-specific, the determinant of the stereo structure of the GP
backbone is limited to G-1-P dehydrogenase and GGGP synthase.
Enzymes in the super family of CDP-alcohol phosphatidyltransferase
(archaetidyl-X synthases)
These polar head-specific enzymes belong to the enzyme super family of
CDP-alcohol phosphatidyltransferase. The enzyme that catalyzes synthesis of
each phospholipid seems to be specific to a polar head group but its reactivity
is not restricted to one type of core lipid. For example, archaetidylserine
synthase shows reactivity with the unnatural substrates, CDP-activated ester
types, sn-G-3-P types and fatty acid types analogs of CDP-archaeol and the
natural substrate, CDP-archaeol [9]. By now, the enzyme activities of
archaetidylserine synthase and archaetidylinositolphosphate synthase [10]
have been characterized in vitro from a methanoarchaeon,
Methanothermobacter thermautotrophicus, while a number of enzymes
belonging to the enzyme superfamily CDP-alcohol phosphatidyltransferase
have been detected on completely-sequenced genomes of Archaea. The
reactions and enzymes up to archaetidic acid synthesis in the archaeal
phospholipid biosynthetic pathway are donated to building for a core lipid,
Early evolution of lipids
349
but the enzymes of CDP-alcohol phosphatidyltransferase family are
contributing to construct an amphiphilic phospholipid that have both a
hydrophobic core portion and hydrophilic polar head group. Because
amphiphilic lipids are essential constituents of biologic membranes, these
enzymes of the family are regarded as membrane-forming enzymes. The
enzymes reacting with most polar head groups and dialkyl ether and diacyl
ester G-1-P and G-3-P core lipids from all three domains of life are all
included in this enzyme family.
4. Functional charateristics of archaeal lipid membrans
Archaeal membranes made of archaeol core and caldarchaeol core and
several polar groups reveal unique characteristics compared with bacterial
fatty acyl ester of G-3-P lipid membranes. Because of isoprenoid
hydrocarbon chains, archaeal lipid membranes have a property of quite low
permeabibility of H+ and other low molecular-weight compounds, and the
low permeability is rather insensitive to temperature. The same kind of lipid
composition of archaeal membrane can adapt to rather wide range of
temperature; i.e., a moderate temperature (37°C)-grown methanoarchaeon
Methanobacterium formicicum and a higher temperature (65°C)-grown
methanoarchaeon Methanothermobacter thermautotrophicus show the same
lipid composition. Caldarchaeol lipids are seen both in hyperthermophilic
Archaea and psychrophilic Archaea. By contrast, bacterial membrane lipid
composition is minutely regulated.
Although an ether-bond itself is hardly cleaved under mild acidic and
heating conditions (for example, 1 M HCl at 100°C for 3 h, under which
condition an ester bond is completely hydrolyzed), ether bond-containing
lipids do not necessarily give thermotolerancy to an organism, since ether
lipids are synthesized via geranylgeranyl ether intermediates, which are one
kind of acid-labile allyl ethers. Because of a tiny amount of this labile allyl
intermediate in the lipid biosynthetic pathway, the heat-stable final product of
saturated ether bonds cannot be synthesized. However, the low permeability
even at rather high temperature is one of the most significant features of
Archaeal membranes (3).
5. How were the membrane lipids of common ancestor cells
composed?
The homologous nature and universal distribution of enzymes of the
family CDP-alcohol phosphatidyltransferase among almost all of the
organisms of the three domains suggest the ancestral enzyme must be present
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Yosuke Koga
in the last common ancestor cells. Genetic and biochemical data suggest the
existence of isoprenoid synthetic system, fatty acid synthase, enzymatic or
pre-biotic synthesis of G-1-P and G-3-P. Because major polar groups are
shared by organisms of all three domains, they are likely also to exist in the
universal common ancestor. Consequently, polar lipids made from chemical
combinations, for example, isoprenoid-G-1-P lipid (Ai), isoprenoid-G-3-P
(Bi) lipid, fatty acid-G-1-P (Af) lipid, and fatty acid G-3-P (Bf) lipid, should
have been present in the universal common ancestor cells.
6. How did differentiation of archaea and bacteria take place?
A question is raised: how the universal common ancestor cells with at
least four types of lipids in their membranes were differentiated into Archaea
and Bacteria, which have solely Ai and Bf lipids, respectively. Several
hypotheses or speculations have been proposed. I do not intend, here, to
review the various arguments, but I summarize a hypothesis that postulates
lipid-driven differentiation [11].
According to Wächtershäuser’s proposal [12], the enantiomeric
difference in GP backbones was the driving force of differentiation of
Archaea and Bacteria from the pre-cells (the common ancestor cells). The
membranes of the pre-cells are composed of lipids with a backbone of
racemic GP (a mixture of G-1-P and G-3-P in equal amounts).
Wächtershäuser postulated that membranes made of mixed GP enantiomers
(heterochiral membranes) are less stable than membranes with higher GP
chirality (i.e., more homochiral membranes), and that the lipid membrane
spontaneously segregated into more homochiral membrane patches.
Pre-cells with more homochiral lipid membranes then underwent
frequent collision, fusion, and division. Consequently, highly homochiral precells (G-1-P-rich pre-cells and G-3-P-rich pre-cells) evolved. During this
process, heterochiral pre-cells became extinct as a result of their instability.
The enzymes, G-1-P dehydrogenase and G-3-P dehydrogenase, induced precells to develop membranes with a pure enantiomeric GP backbone. These
cells became the ancestors of Archaea and Bacteria, respectively.
If four types core lipids existed in the universal common ancestor
cells, the segregation of membrane phospholipids with the G-1-P
backbone with either isoprenoid or fatty acids (Ai or Af) and the G-3-P
lipid with either isoprenoid or fatty acids (Bi or Bf). To segregate and
survive as Ai and Bf lipids, not only the GP enantiomer backbones but
also the hydrocarbon chains must be involved in this process. A
hypothetical mechanism for the segregation of the four core lipids was
quite recently proposed [11].
Early evolution of lipids
351
Figure 4. Diastereomers of diphytanylglycerol (archaeol). The stereochemical
configuration of three chiral centers were established by Kates et al [13] as all R. The
configuration of the C2 positions of G-1-P and G-3-P are S and R, respectively.
Therefore, Ai has S,R,R,R,R,R,R configuration, and Bi has R,R,R,R,R,R,R
configuration, which are diastereomers each other.
Enantiomeric GP backbones are assumed to be the main driving force for
membrane segregation. In addition, different types of hydrocarbon chains
would prompt segregation of the two lipids. Isoprenoid chains and typical
fatty acid chains have largely different molecular shapes; isoprenoid chains
are characterized by four methyl branches on the main chain at every four
carbon atoms, and most isoprenoid chains of archaeal phospholipids are
saturated, whereas fatty acyl chains have no or only one methyl branch and
often have a cis double bond, at which the chain is kinked. Thus, the
physicochemical properties of these chains differ and the effect of the
hydrocarbon interaction on segregation is significant.
Since the stereo structure of the whole molecule of Ai and Bi are
diastereomers (seven chiral centers of diphytanyl-G-1-P is S,R,R,R,R,R,R; of
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Yosuke Koga
diphytanyl-G-3-P is R,R,R,R,R,R,R,), while Bf and Af are enantiomers (Only
one chiral center of difatty acyl-G-1-P and difatty acyl-G-3-P are S and R,
respectively), the tendency toward segregation of Ai:Bf seems to be higher
than Af:Bi, because diastereomers have different physicochemical properties
as different compounds, whereas enantiomers have identical properties
except for their chiral properties (Fig. 4). Consequently, descendent cells with
Ai lipid membranes became the ancestor of Archaea and descendent cells
with Bf lipid membranes became the ancestor of Bacteria. The Ai and Bf
lipids are clearly segregated. Auto (self) segregation of homochiral lipid
membranes is one of the driving forces of the differentiation of Archaea and
Bacteria, i.e., the “lipid divide” is caused by membrane-driven evolution.
7. Membrane-driven differentiation
If Archaea and Bacteria were differentiated by causes other than the
segregation of homochiral lipid patches, Archaea and Bacteria would have an
equal mix of Ai type and Bf type lipids, because lipids are in a fluid state
(Singer and Nicholson, 1972) and a variety of lipid species would be mixed
in the membrane. This is not the case. The common distribution of
phospholipid polar head groups may indicate that both polar head groups and
their synthesizing systems were equally transferred to Archaea and Bacteria
through the fission (division) of pre-cells. This, in turn, suggests that polar
head groups are not a driving force in the differentiation of Archaea and
Bacteria. The fact that Archaea and Bacteria possess common polar groups
and enzymes suggests the presence of common ancestor cells in which polar
head groups and their synthesizing systems already existed.
The cytoplasm is equally divided into both daughter cells. This is the
reason for the common occurrence of polar groups in archaeal and bacterial
phospholipids. CDP-alcohol phosphatidyltransferase enzymes were equally
distributed in the both domains of organisms even though they were
membrane-bound enzymes but they were not a driving force of membrane
segregation.
8. Archaea research illuminate the biochemistry concerning
E. coli and B. subtilis by a backlight
It is needless to say that studies of E. coli and B. subtilis of half a century
duration achieved magnificent results, which constructed major principles of
molecular biology applicable to all the living organisms. The both
microorganisms contributed creation of general principle of modern biology
beyond their individual peculiarity. Phenomena, or biochemical mechanisms
Early evolution of lipids
353
even peculiar to E. coli and B. subtilis were, occasionally, unpremeditatedly
believed to be applicable to other organisms. However, some of research
results of Archaea, which have many features strikingly different from
bacterial species, illuminate an important property among biochemical
properties of Bacteria from the other side. For example, the significance of
G-3-P backbone of glycerolipids was first recognized when the backbone of
archaeal lipids was found to be enantiomeric G-1-P without exception.
Before then, the lipid backbone of all the organisms was believed to be G-3P. Since archaeal G-1-P was found, G-3-P is merely one of the two types of
GP backbones. Archaeal study illuminates from the reverse side what is
important. The other example is substrate specificity of CDP-archaeol (CDPdiacylglycerol):serine
archaetidyl
(phosphatidyl)
transferase
(archaetidyl(phosphatidyl)serine synthase = AS (PS) synthase). AS synthase
was found to be active towards CDP-1, 2-digeranylgeranyl-sn-glycerol, CDP2, 3- digeranylgeranyl-sn-glycerol, CDP-1, 2-diacyl-sn-glycerol, CDP-2, 3diacyl-sn-glycerol as well as CDP-2, 3-digeranylgeranyl-sn-glycerol. This
shows the archaeal enzyme was active to the bacterial-type lipid substrate.
Next the bacterial counterpart enzyme (PS synthase) was tested for its
substrate specificity. The enzyme was also active towards all the above
substrates. This property of the enzyme was inconceivable until archaeal
biochemical studies achieved a measure of success.
Although E. coli and B. subtilis are thoroughly investigated, they are not
typical examples of organisms. Phenomena or mechanisms observed in those
microorganisms should not be imprudently generalized. A number of
mechanisms of metabolic regulation are greatly developed in E. coli. This is
due to the habitats of the organism; E. coli usually lives in human intestine,
where is warm, anoxic, and rich in nutritious organic materials, but is often
released from the intestine to the outside of the host body, where is less
warm, oxic, and poor in nutrition. E. coli is usually going back and forth
between the two environments. To adapt, survive, and thrive in the often
changes of habitat conditions, the organism have developed unique
regulatory mechanisms of metabolism. For example, repression and allosteric
inhibition were also first discovered in E. coli. There are rarely found
microorganisms that inhabit two interchangeable, different environments;
many inhabit one constant environment. When E. coli grows low temperature
(e.g., 17oC), its membrane lipid is composed of more unsaturated fatty acid
compared with the membrane lipid from cells grown at higher temperature
(e.g., 37oC). Misconception about this phenomenon is often seen by
unreasonable application to other microorganisms of increase of double
bonds in lipid hydrocarbon chains as adaptation to lower temperature. In
B. subtilis, little unsaturated fatty acid is present in the membrane lipids, and
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Yosuke Koga
their change in composition is insignificant for adaptation to different growth
temperature. Instead of unsaturated fatty acid, anteiso methyl branched fatty
acid increased. Archaeal isoprenoid lipids keep lower permeability of
hydrogen ion and low molecular weight compounds throughout temperature
organisms are living, while bacterial straight chain alkyl chains must be
regulated to a narrow range of fatty acid composition that shows just above
phase transition temperature. Therefore, Archaea, in general, does not change
their isoprenoid composition during growth temperature change. Thus,
response in membrane lipid composition to growth temperature is different
depending on species. E. coli is not at all the typical representative of
organism, but a unique species in Bacteria.
There have been known PS synthase type II and I. The type I enzyme
was first found in E. coli. The type II enzyme was later found in B. subtilis
and many other Bacteria and Archaea. Studies on lipid biosynthesis begin to
illuminate what is ubiquitous and what is peculiar. As a results, it is clarfied
that ubiquity represents on the peculiarities. Advances in studies on
Archaea, which are the most distantly related with Bacteria, would supply
unexpected but significant development to bacterial science.
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Footnote
1. sn, stereospecific numbering. One of the nomenclatures of stereo isomers
of the glycerol backbone of glycerolipids. Glycerol is a non chiral molecule
but pro-chiral. The pro-S carbon is designated sn-1. sn-Glycerol-3-phosphate
Early evolution of lipids
355
corresponds to L-glycerol-3-phosphate, which is the backbone of bacterial
and eukaryal membrane lipids. sn-Glycerol-3-phosphate is the enantiomer of
sn-glycerol-1-phosphate, which is in the archaeal membranes.
2. Diastereomers: Compounds which have two or more chiral centers and
are not enantiomers each other. While enantiomers show the same
physicochemical properties except for stereochemical properties,
diastereomers are different in nature as different compounds.