Microbial Membrane Lipids Research Articles

Archaeal and bacterial lipids in authigenic carbonate crusts from eastern Mediterranean mud volcanoes

We investigated the distributions and δ 13C values of lipid biomarkers in authigenic methane-related carbonate crusts formed on eastern Mediterranean mud volcanoes. A highly diverse suite of microbial membrane lipids was detected. Strongly 13C-depleted lipids diagnostic for archaea include isoprenoid glycerol diethers, isoprenoid glycerol dialkyl glycerol tetraethers and several C 20–C 35 isoprenoid hydrocarbons. Bacterial lipids mainly consist of dialkyl glycerol diethers, branched fatty acids and hopanoids, showing important 13C-depletions, albeit less than archaeal lipids. The data provide further evidence for the involvement of archaea and bacteria in the anaerobic oxidation of methane (AOM) and in the sequestration of methane-derived carbon in authigenic carbonate crusts. Varying distributions and isotopic compositions of 13C-depleted lipids argue for heterogeneous AOM-related microbial consortia, expanding on existing work at cold seeps. Distinctive biomarker features – and inferred microbial assemblages – are observed in these crusts, in agreement with available phylogenetic data for the samples. Our results support the potential of lipids for distinguishing methanotrophic communities. Despite the observed variances, conservative features in the abundances and isotopic offsets of microbial biomarkers occur, likely reflecting the overall relationships between archaea and bacteria and the nature of carbon flow between them.

Variation in NH 4+ mineralization and microbial communities with stand age in lodgepole pine ( Pinus contorta) forests, Yellowstone National Park (USA)

Soils and vegetation were analyzed in 20 lodgepole pine ( Pinus contorta) forest stands, varying in age from 50 to 350 years, that had initiated following stand-replacing fire. Our goal was to determine how nitrogen availability (NH 4 +–N) and microbial community composition varied with stand age-class and to determine whether differences could be explained by canopy, soil, or understory characteristics. Gross NH 4 + mineralization was measured using laboratory isotopic pool dilution, and microbial community composition was evaluated using microbial membrane lipids. The microbial community composition of stands in the 300–350 age class was distinct from stands in younger age classes. Microbial community composition among sites varied with pH, % organic matter, and phosphorus. Gross NH 4 + mineralization rates averaged 1.45±0.07 mg NH 4 + kg soil −1 d −1 while consumption averaged 1.37±0.20 mg NH 4 + kg soil −1 d −1, resulting in low net NH 4 + mineralization rates (0.08±0.18 mg NH 4 + kg soil −1 d −1), but rates were not significantly different with stand age-class at p<0.05. At p<0.10, net NH 4 + mineralization was significantly higher in the 300–350 age class compared to the 125–175 age class. None of the measured variables significantly explained NH 4 + consumption and net mineralization patterns. However, gross NH 4 + mineralization rates were best explained by information on microbial community structure (i.e. lipids). Variation among stands within a given age-classes was high, indicating that patterns of N cycling across landscapes reflect substantial heterogeneity among mature stands.

Linearly concatenated cyclobutane lipids form a dense bacterial membrane.

Lipid membranes are essential to the functioning of cells, enabling the existence of concentration gradients of ions and metabolites. Microbial membrane lipids can contain three-, five-, six- and even seven-membered aliphatic rings, but four-membered aliphatic cyclobutane rings have never been observed. Here we report the discovery of cyclobutane rings in the dominant membrane lipids of two anaerobic ammonium-oxidizing (anammox) bacteria. These lipids contain up to five linearly fused cyclobutane moieties with cis ring junctions. Such 'ladderane' molecules are unprecedented in nature but are known as promising building blocks in optoelectronics. The ladderane lipids occur in the membrane of the anammoxosome, the dedicated intracytoplasmic compartment where anammox catabolism takes place. They give rise to an exceptionally dense membrane, a tight barrier against diffusion. We propose that such a membrane is required to maintain concentration gradients during the exceptionally slow anammox metabolism and to protect the remainder of the cell from the toxic anammox intermediates. Our results further illustrate that microbial membrane lipid structures are far more diverse than previously recognized.

Effect of Some Environmental Factors on the Content and Composition of Microbial Membrane Lipids

Lipids are known as a part of an effective adaptation mechanism reflecting the changes in the extracellular environment. The fluidity of biological membranes is influenced by the lipid structure and the portion of saturated, unsaturated, branched, or cyclic fatty acids in individual phospholipids. For all living organisms undergoing environmental adaptation, the fluidity can be changed only to a relatively small extent. This range is genetically determined and it is specific for every microorganism. This article presents recent knowledge about the influence of some environmental parameters (temperature, osmotic pressure, pH, the presence of salt or ethanol in medium) on a microbial membrane with the emphasis on regulation aspect in fatty acid biosynthesis. The main tools for regulation of membrane fluidity, for example, fatty acid desaturation or incorporation of branched and cyclic fatty acids into phospholipids, are discussed in more detail.