Variable temperature-related changes in fatty acid composition of bacterial isolates from German Wadden sea sediments representing different bacterial phyla

erial strains, including 15 facultative anaerobes and 9 strictly anaerobic sulfate reducers, were isolated under anoxic conditions from an intertidal mudflat of the northwest German coast and analysed for temperature-induced changes in their whole cell fatty acid (FA) patterns. The strains represented 10 different genera within the Alpha, Gamma, Delta and Epsilon subgroups of the Proteobacteria, Firmicutesand Actinobacteria. The strains differed with respect to variation in FA patterns with changing growth temperature. For most strains, decreasing growth temperature resulted in an increase in monounsaturated FAs and a decrease in saturated straight chain FAs, as expected from literature data. Often these changes did not occur gradually over the whole temperature range. Changes in branched FAs, reported to be involved in adaptation to low temperature, increased with decreasing temperature in Bacillus and Shewanella spp., whereas in Desulfovibrio spp. an opposite effect was observed. Only minor changes in chain length or in the ratio of anteiso to iso FAs were observed in the entire set of isolates. Surprisingly, several strains did not show any change at all in FA pattern over the temperature range tested (10–30 °C). Moreover, significant differences in the way the isolates adjusted membrane fluidity to changing temperature were not only found between members of different phyla, but also among strains of a single genus (e.g. Shewanella and Desulfovibrio). The results therefore indicate that there is no unequivocal way as to how bacteria change their membrane FA composition in response to changing temperature and that it is virtually impossible to predict potential changes. Consequently, using the FA composition for taxonomic resolution is problematical

Pristane/phytane ratio as environmental indicator - Reply

We agree with Powell that pristane (Pr) to phytane (Ph) ratios close to unity should be interpreted with great caution and that fewer difficulties arise with extremely high (as in coals) or extremely low (as in sediment from hypersaline environments) Pr/Ph ratios. In these latter cases, the Pr/Ph ratios are probably influenced by specific sources of the organic matter and specific depositional environments, where the redox condition is only one of the factors. The main point of our paper concerns the generalizations and oversimplifications implied in the use of the Pr/Ph ratio as an indicator of the level of oxygen at the site of organic matter deposition into sediments. We made several new arguments based on novel geochemical findings to emphasize the restricted use of the Pr/Ph ratio as a palaeoenvironmental indicator. Of course, we do not object to using the Pr/Ph ratio as a correlative tool when samples of the same origin and maturation level are compared with one another (as in oil/source-rock correlation)

Petrography and Geochemistry of Organic Matter in Triassic and Cretaceous Deep-Sea Sediments from the Wombat and Exmouth Plateaus and nearby Abyssal Plains off Northwest Australia

The dominant vitrinites and inertinites are hydrogen-lean, and the small quantities of extractable bitumen contain n-alkanes and bacterial hopanoid hydrocarbons as the most dominant single gas-chromatography-amenable compounds. Lower Cretaceous sediments on the central Exmouth Plateau (Sites 762 and 763) farther south in general have an organic matter composition similar to that in the Wombat Plateau sediments with the exception of a smaller particle size of vitrinites and inertinites, indicating more distal transport and probably deposition in deeper water. Differences in organic matter accumulation at the Cenomanian/Turonian boundary at different sites off northwest Australia are ascribed to regional variations in primary bioproductivity. -from Author

Restricted utility of the pristane/phytane ratio as a palaeoenvironmental indicator?

The acyclic C₁₉ and C₂₀ isoprenoid hydrocarbons, pristane (Pr) and phytane (Ph), respectively, have been widely assumed to be diagenetic products of the phytyl side chain of chlorophyll¹⁻³, although alternative sources of precursors have been suggested. The ratio of these two compounds is usually interpreted to be an indicator of the oxicity of the environment of deposition. Recent advances in organic geochemistry in combination with geological constraints lead us to suggest that the Pr/Ph ratio cannot be used as an indicator for oxygen levels. However, in hypersaline environments of deposition the rationale behind a low Pr/Ph ratio is easier to understand, and in these environments application of the Pr/Ph ratio can be expected to be successful

Distribution of organic sulphur compounds in Mesozoic and Cenozoic sediments from the Atlantic and Pacific Oceans and the Gulf of California

Gas chromatography-mass spectrometry data of the "aromatic hydrocarbon" fractions of nearly 100 Deep Sea Drilling Project and Ocean Drilling Program sediment samples have been re-examined for the occurrence of organic sulfur compounds. Approximately 70% of the samples contain OSC with varying distribution patterns, although C₂₀ isoprenoid thiopenes are invariably present