Surface sediments collected from 40 stations in Ise Bay, which is one of the most polluted bays in Japan, were subjected to phospholipid ester-linked fatty acid (PLFA) analysis. Thirty-five fatty acids were identified in the sediments
they included saturated, unsaturated and branched fatty acids. The major fatty acids included the even-numbered straight chain fatty acid 16:0 (20%), branched chain fatty acids i15:0 (8%) and a15:0 (11%),and monounsaturated fatty acids 16:1d9c (11%) and 18:1d11 (10%). Fatty acids which are common in bacterial membranes were found, and low amounts of longer chain fatty acids were detected in relatively constant amounts in the bay. One of the characteristic features of the PLFA analysis in Ise Bay is the virtual absence of polyunsaturated fatty acids in the sediments, except for 18:2. The PLFA profiles indicate that the microbial community structure is characterized by the absence of polyunsaturated fatty acids typical of microeukaryotes and high proportions of fatty acid biomarkers of prokaryotes in sediments. A wide distribution of aerobic bacteria. Gram-positive bacteria, anaerobic bacteria and sulfate-reducing bacteria in the microbial community structure was indicated by the presence of biomarker fatty acids. Similarity analysis of the PLFA profiles in sediments of all the stations showed that they were similar at the 90% level. The results of Tukey's test showed that a majority of the fatty acids in sediments were not significantly enriched in the bay. The absence of significant variation in the PLFA profiles in sediments revealed that the microbial community structure is similar throughout the bay, and this uniformity was attributed to the reported pollution and eutrophication in Ise Bay. Further, the significant PLFA patterns, with a high proportion of prokaryotic biomarker fatty acids and an absence of microeukaryotic biomarkers, indicate that PLFA analysis could be used as a measure of pollution in sediments. © 1993.