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

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