Summary: The phospholipid ester-linked fatty acids were examined in four strains (2ac9, AcBa, 3ac10 and 4ac11), a -like ‘fat vibrio’ (AcKo) and (5575), which are all sulphate-reducing bacteria that oxidize acetate. A thermophilic sulphate reducer, , and two sulphur-reducing bacteria, (11070) and a -like spirillum (5175), were also studied. The spp. were characterized by significant quantities of 10-methylhexadecanoic acid. Other 10-methyl fatty acids were also detected in spp. No 10-methyl fatty acids were detected in the other organisms examined, supporting the use of 10-methylhexadecanoic acid as a biomarker for . High levels of cyclopropyl fatty acids, including two isomers of both methylenehexadecanoic (cy17:0) and methyleneheptadecanoic (cy18:0) acids, were also characteristic of spp. The influence of the volatile fatty acids (VFA) propionate, isobutyrate, isovalerate and 2-methylbutyrate on the lipid fatty acid distribution was studied with two strains (2ac9, AcBa) and . Although these sulphate reducers cannot oxidize the VFA, their presence in the acetate growth medium caused a shift in the fatty acid distribution in favour of odd-numbered and branched chains by apparent direct incorporation into the fatty acids as chain initiators. The strains were distinguished from other sulphide-forming bacteria by the percentage of unsaturated and the percentage of branched fatty acids.


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