The Polar and Neutral Lipid Composition of Methanosphaera stadtmanae

Fatty acid synthesis in Escherichia coli and its applications towards the production of fatty acid based biofuels

The idea of renewable and regenerative resources has inspired research for more than a hundred years. Ideally, the only spent energy will replenish itself, like plant material, sunlight, thermal energy or wind. Biodiesel or ethanol are examples, since their production relies mainly on plant material. However, it has become apparent that crop derived biofuels will not be sufficient to satisfy future energy demands. Thus, especially in the last decade a lot of research has focused on the production of next generation biofuels. A major subject of these investigations has been the microbial fatty acid biosynthesis with the aim to produce fatty acids or derivatives for substitution of diesel. As an industrially important organism and with the best studied microbial fatty acid biosynthesis, Escherichia coli has been chosen as producer in many of these studies and several reviews have been published in the fields of E. coli fatty acid biosynthesis or biofuels. However, most reviews discuss only one of these topics in detail, despite the fact, that a profound understanding of the involved enzymes and their regulation is necessary for efficient genetic engineering of the entire pathway. The first part of this review aims at summarizing the knowledge about fatty acid biosynthesis of E. coli and its regulation, and it provides the connection towards the production of fatty acids and related biofuels. The second part gives an overview about the achievements by genetic engineering of the fatty acid biosynthesis towards the production of next generation biofuels. Finally, the actual importance and potential of fatty acid-based biofuels will be discussed.

Posttranslational protein modification in Archaea

One of the first hurdles to be negotiated in the postgenomic era involves the description of the entire protein content of the cell, the proteome. Such efforts are presently complicated by the various posttranslational modifications that proteins can experience, including glycosylation, lipid attachment, phosphorylation, methylation, disulfide bond formation, and proteolytic cleavage. Whereas these and other posttranslational protein modifications have been well characterized in Eucarya and Bacteria, posttranslational modification in Archaea has received far less attention. Although archaeal proteins can undergo posttranslational modifications reminiscent of what their eucaryal and bacterial counterparts experience, examination of archaeal posttranslational modification often reveals aspects not previously observed in the other two domains of life. In some cases, posttranslational modification allows a protein to survive the extreme conditions often encountered by Archaea. The various posttranslational modifications experienced by archaeal proteins, the molecular steps leading to these modifications, and the role played by posttranslational modification in Archaea form the focus of this review.

Phospholipid etherlipid and phospholipid fatty acid fingerprints in selected euryarchaeotal monocultures for taxonomic profiling

Phospholipid etherlipid (PLEL) derived isoprenoids and phospholipid fatty acids (PLFA) were determined in eight Euryarchaeotal monocultures for taxonomic profiling. For the first time significant amounts of fatty acids in the PLFA of Euryarchaeota were determined. The PLFA proportion varied between 11.3 and 35.5% of the total phospholipid side chains except in Methanothermus fervidus where PLFA accounted for 89.0% of the total phospholipid side chains. Fractionation of fatty acids prior to gas chromatography mass spectrometry analysis revealed that non-ester-linked fatty acids dominated which accounted for 85.5-95.2% of total PLFA in all investigated archaeal strains. PLEL concentration and composition was estimated in accordance with previous studies with two exceptions. In the polar (phospho)lipid fraction of Methanopyrus kandleri side chains possibly derived from hydroxyarchaeol as well as acyclic and cyclic caldarchaeol were identified. In phospholipid extracts of Methanothermus fervidus the 'H-formed' caldarchaeol could not be detected. Overall, PLEL derived isoprenoids as well as PLFA enabled taxonomic differentiation of the selected microorganisms into phylogenetically related groups.

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.

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.