A diphytanyl ether analog of phosphatidylserine from a methanogenic bacterium, Methanobrevibacter arboriphilus

Selective chemical degradation of silica sinters of the Taupo Volcanic Zone (New Zealand). Implications for early Earth and Astrobiology

Most organic matter (OM) on Earth occurs as kerogen-like materials, that is naturally formed macromolecules insoluble with standard organic solvents. The formation of this insoluble organic matter (IOM) is a topic of much interest, especially when it limits the detection of compounds of geomicrobiological interest. For example, studies that search for biomarker evidence of life on early Earth or other planets usually use solvent-based extractions. This leaves behind a pool of OM as unexplored post-extraction residues, potentially containing diagnostic biomarkers. Since the IOM has an enhanced potential for preservation compared to soluble OM, analysing IOM-released biomarkers can also provide even deeper insights into the ecology of ancient settings, with implications for early Earth and Astrobiology investigations. Here, we analyse the prokaryotic lipid biosignature within soluble and IOM of the Taupo Volcanic Zone (TVZ) silica sinters, which are key analogues in the search for life. We apply sequential solvent extractions and a selective chemical degradation upon the post-solvent extraction residue. Moreover, we compare the IOM from TVZ sinters to analogous studies on peat and marine sediments to assess patterns in OM insolubilisation across the geosphere. Consistent with previous work, we find significant but variable proportions-1%-45% of the total prokaryotic lipids recovered-associated with IOM fractions. This occurs even in recently formed silica sinters, likely indicating inherent cell insolubility. Moreover, archaeal lipids seem more prone to insolubilisation as compared to the bacterial analogues, which might enhance their preservation and also bias overall biomarkers interpretation. These observations are similar to those observed in other settings, confirming that even in a setting where the OM derives predominantly from prokaryotic sources, patterns of IOM formation/occurrence are conserved. Differences with other settings, however, such as the occurrence of archaeol in IOM fractions, could be indicative of different mechanisms for IOM formation that merit further exploration.

Linear Aminolipids with Moderate Antimicrobial Activity from the Antarctic Gram-Negative Bacterium Aequorivita sp

The combination of LC-MS/MS based metabolomics approach and anti-MRSA activity-guided fractionation scheme was applied on the Gram-negative bacterium Aequorivita sp. isolated from shallow Antarctic sea sediment using a miniaturized culture chip technique. This methodology afforded the isolation of three new (1⁻3) and four known (4⁻7) N-terminal glycine- or serine-bearing iso-fatty acid amides esterified with another iso-fatty acid through their C-3 hydroxy groups. The chemical structures of the new compounds were elucidated using a set of spectroscopic (NMR, [α]_D and FT-IR) and spectrometric (HRMS, HRMS/MS) methods. The aminolipids possessing an N-terminal glycine unit (1, 2, 4, 5) showed moderate in vitro antimicrobial activity against MRSA (IC₅₀ values 22⁻145 μg/mL). This is the first in-depth chemistry and biological activity study performed on the microbial genus Aequorivita.

A structural comparison of the total polar lipids from the human archaea Methanobrevibacter smithii and Methanosphaera stadtmanae and its relevance to the adjuvant activities of their liposomes

Mice were immunized with bovine serum albumin (BSA) entrapped within archaeosomes (i.e. liposomes) composed of the total polar lipids (TPL) from the two methanogenic archaea common to the human digestive tract. Methanobrevibacter smithii archaeosomes boosted serum anti-BSA antibody to titers comparable to those achieved with Freund's adjuvant, whereas Methanosphaera stadtmanae archaeosomes were relatively poor adjuvants. An explanation for this difference was sought by analysis of the polar lipid composition of each archaeobacterium. Fast atom bombardment mass spectrometry and NMR analyses of the purified lipids revealed a remarkable similarity in the ether lipid structures present in each TPL extract. However, the relative amounts of each lipid species varied dramatically. The phospholipid fraction in M. stadtmanae TPL was dominated by archaetidylinositol (50 mol% of TPL) and the glycolipid fraction by beta-Glcp-(1,6)-beta-Glcp-(1,1)-archaeol (36 mol%), whereas in M. smithii extracts, both caldarchaeol and archaeol lipids containing a phosphoserine head group were relatively abundant. Liposomes prepared from purified archaetidylinositol and from M. stadtmanae TPL supplemented with increasing amounts of phosphatidylserine elicited poor humoral responses to encapsulated BSA. A dramatic loss in the adjuvanticity of M. smithii archaeosomes was seen upon incorporation of 36 mol% of the uncharged lipid diglucosyl archaeol and, to a lesser extent, of 50 mol% of archaetidylinositol. Interestingly, the relative rates of uptake of M. smithii and M. stadtmanae archaeosomes by phagocytic cultures in vitro were similar. Thus, the lipid composition may influence archaeosome adjuvanticity, particularly a high diglucosyl archaeol and/or archaetidyl inositol content, resulting in a low adjuvant activity.

A novel phosphoglycolipid archaetidyl(glucosyl)inositol with two sesterterpanyl chains from the aerobic hyperthermophilic archaeon Aeropyrum pernix K1

The structures of two novel polar lipids (AGI and AI) of an aerobic hyperthermophilic archaeon, Aeropyrum pernix, were elucidated. AGI and AI were the only two major lipids and accounted for 91 mol% and 9 mol%, respectively, of total polar lipids of this organism. The core lipid of A. pernix total lipids consisted solely of 2,3-di-O-sesterterpanyl-sn-glycerol (C25,25-archaeol). The molecular weights of the free acid forms of AGI and AI were shown by FAB-mass spectrometry to be 1196 and 1034, respectively. AI was completely hydrolyzed by phosphatidylinositol-specific phospholipase C, while AGI was not hydrolyzed at all under the same condition for the hydrolysis of AI. The molar ratio of phosphate, myo-inositol, and glucose in AGI was 1.0:0.97:0.95. The positions of linkages between myo-inositol and glucose, and between myo-inositol and phosphate in AGI were determined by NMR analyses of intact AGI and glucosylinositol prepared from AGI. Finally, it was concluded that the structures of AGI and AI were 2,3-di-O-sesterterpanyl-sn-glycerol-1-phospho-1'-(2'-O-alpha-D-glu cosyl)- myo-inositol (C25,25-archaetidyl(glucosyl)inositol) and 2,3-di-O-sesterterpanyl-sn-glycerol-1-phospho-myo-inositol (C25,25-archaetidylinositol), respectively. This is the first example that a core lipid of whole polar lipids is composed of only one species C25,25-archaeol in one organism and that glucosylinositol is found in a polar lipid as a polar head group.

A novel ether core lipid with H-shaped C80-isoprenoid hydrocarbon chain from the hyperthermophilic methanogen Methanothermus fervidus

A new ether lipid core (designated as FU) was found in Methanothermus fervidus total lipid. Comparison with caldarchaeol showed lower mobility of FU on TLC and smaller molecular weight (m/z 1298) by 2 mass units on FAB-MS. Treatment of FU with HI followed by displacement with silver acetate afforded long chain alcohol acetate (ROAc), which was further saponified with mild alkali to its free alcohol (ROH). ROH is the long chain alcohol prepared from FU. The molecular weights of ROAc and ROH were shown by MS to be 1354 and 1186, respectively. These results suggested that the molecular formula of ROH was C80H162O4, and ROH had four hydroxyl groups, and one molecule of ROH was bound with two molecules of glycerol by four ether linkages. Because FU was not oxidized by NaIO4 and specific rotation [alpha]D of FU coincided with that of caldarchaeol, it seems that the ether linkages of FU are formed with hydroxyl groups of the sn-2 and sn-3 positions of each glycerol moiety. The structure of FU was suggested to be a modified caldarchaeol in which two hydrocarbon chains are bridged with a covalent bond. Although a few points remain to be elucidated before the final conclusion can be reached on the structure of FU due to difficulty in complete structure determination done even with every approach currently available, the most possible position of the bridge in FU hydrocarbon was proposed from the data of EI-MS of ROAc and 1H-NMR of FU. The hydrocarbon chain looks like H-shaped C80 isoprenoid.

Two new phospholipids, hydroxyarchaetidylglycerol and hydroxyarchaetidylethanolamine, from the Archaea Methanosarcina barkeri

The structures of two new ether phospholipids of the methanogenic Archaea, Methanosarcina barkeri, were determined as hydroxyarchaetidylglycerol and hydroxyarchaetidylethanolamine by means of chemical, chromatographic and enzymatic analyses, and fast atom bombardment-mass spectrometry. These lipids are hydroxy diether analogs of phosphatidylglycerol and phosphatidylethanolamine, respectively, with beta-hydroxyarachaeol (2-O-(3'-hydroxy)phytanyl-3-O-phytanyl-sn-glycerol) as a core lipid. In addition, two other ether phospholipids, usual archaetidylglycerol and archaetidylethanolamine, were also identified in the organism. The stereochemical structure of the unalkylated glycerophosphate of hydroxyarchaetidylglycerol and archaetidylglycerol was determined as sn-glycerol-3-phosphate by use of sn-glycerol-3-phosphate dehydrogenase. The stereochemical configuration of the glycerophosphoglycerol backbone of these lipids was a mirror image of that of diacylphosphatidylglycerol from the organisms of the domains Bacteria and Eucarya, and it was shared with extremely halophilic Archaea. These four phospholipids, in addition to five lipids that had already been reported, accounted for 88% of the total polar lipids of this organism.

Structures of archaebacterial membrane lipids

Structural data on archaebacterial lipids is presented with emphasis on the ether lipids of the methanogens. These ether lipids normally account for 80-95% of the membrane lipids with the remaining 5-20% of neutral squalenes and other isoprenoids. Genus-specific combinations of various lipid core structures found in methanogens include diether-tetraether, dietherhydroxydiether, or diether-macrocyclic diether-tetraether lipid moieties. Some species have only the standard diether core lipid, but none are known with predominantly tetraether lipids as found in certain sulfur-dependent archaebacteria. The relative proportions of these lipid cores are known to vary in relation to growth conditions in Methanococcus jannaschii and Methanobacterium thermoautotrophicum. Polar headgroups in glycosidic or phosphodiester linkage to the sn-1 or sn-1' carbons of glycerol consist of polyols, carbohydrates, and amino compounds. The available structural data indicate a close similarity among the polar lipids synthesized within the species of the same genus. Detection of lipid molecular ions by mass spectrometry of total polar lipid extracts is a promising technique to provide valuable comparative data. Since these lipid structures are stable within the extreme environments that many archaebacteria inhabit, there may be specific applications for their use in biotechnology.

Phospholipids and a novel glycine-containing lipoamino acid in Cytophaga johnsonae Stanier strain C21

Two-dimensional thin-layer chromatography revealed that Cytophaga johnsonae contains at least 10 kinds of lipid, 2 of which are phospholipids, namely, phosphatidylethanolamine and phosphatidylcholine. One of the remaining lipids is a novel lipid that contains an amino acid. The structure of this unusual lipid (lipoamino acid) was resolved by chemical and physicochemical methods. The fatty acyl moiety of this lipid was diverse. The structure of the major molecular species of the lipid was determined as iso-3-hydroxy heptadecanoic acid, amide linked to glycine and esterified to isopentadecanoic acid. This type of glycine-containing lipid is a novel biological material which we have called cytolipin, basing this nomenclature on the genus of the bacterium. This is the first report of the lipid composition of C. johnsonae.

Hydroxyarchaetidylserine and hydroxyarchaetidyl-myo-inositol in Methanosarcina barkeri: polar lipids with a new ether core portion

Lipids of the methanogenic archaebacterium, Methanosarcina barkeri were analyzed. The lipid content was 5.4% of dry cell and polar lipids comprised 87% of the total lipid. Polar lipids were separated into 14 spots by two-dimensional thin-layer chromatography. These were six phospholipids, seven aminophospholipids and one glycolipid, of which two phospholipids and two aminophospholipids were major constituents. After removal of polar head groups from total lipids, two kinds of glycerol diether core lipids were found. One was 2,3-di-O-phytanyl-sn-glycerol (archaeol) and the other 2-O-(3'-hydroxy-3', 7', 11', 15'-tetramethyl)hexadecyl-3-O-phytanyl-sn- glycerol (hydroxyarchaeol). Those structures were identified on the basis of chemical analysis, fast atom bombardment spectrometry, gas-liquid chromatography-mass spectrometry and 1H- and 13C-NMR spectrometry. The latter was a new core lipid which was different from hydroxyarchaeol of Methanothrix concilii. The hydroxyarchaeol core lipid comprised 60% of polar lipid in M. barkeri. The structures of core lipids are quite different from those previously reported by De Rosa et al. (Biochim, Biophys. Acta (1986) 875, 487-492) concerning M. barkeri lipids. The structures of two major polar lipids, both of which had hydroxyarchaeol as core proteins, were elucidated. These lipids were 2-O-(3'-hydroxy)phytanyl-3-O-phytanyl-sn-glycero-1-phosphoserine (hydroxyarchaetidylserine) and 2-O-(3'-hydroxy)phytanyl-3-O-phytanyl-sn- glycerol-phospho-myo-inositol (hydroxyarchaetidyl-myo-inositol). Archaetidylserine and archaetidylinositol, which had the usual archaeol core portion, were also present as minor polar lipids.