Characterization ofMicrobial Community Structure inthe Surface Sediment ofOsakaBay,Japan, byPhospholipid Fatty AcidAnalysis

Twenty-eight sediment samples collected fromOsakaBay,Japan, were analyzed forphospholipid esterlinked fatty acids (PLFA) todetermine regional differences inmicrobial community structure ofthebay.The abundance ofthree majorgroupsofC10toClgPLFA(saturated, branched, andmonounsaturated PLFA), whichaccounted for84to97%ofthetotal PLFA,indicated thepredominance ofprokaryotes inthesediment. Thedistribution ofsixclusters obtained bysimilarity analysis inthebayrevealed a markedregional distribution inthePLFAprofiles. Total PLFAconcentrations (0.56 to2.97,g/g[dry weight] ofthesediment) insediments also showed markedvariation among thestations, withhigher concentrations oftotal PLFAinthe central partofthebay.Thebiomass, calculated on thebasis oftotal PLFA concentration, ranged from0.25 x 108to1.35x 108cells per g (dryweight) ofthesediment. Therelative dominance ofmicrobial groupsin sediments was described byusing thereported bacterial biomarker fatty acids. Verysmallamountsofthe characteristic PLFAofmicroeukaryotes insediments indicated therestricted distribution ofmicroeukaryotes. By examining thedistribution ofclusters andgroupsofmicroorganisms inthebay,therewere two characteristics ofthedistribution pattern: (i)thepredominance ofanaerobic bacteria andgram-positive prokaryotes, characterized bythehighproportions ofbranched PLFAintheeastern andnortheastern sides of thebay,wherethereported concentrations ofpollutants were alsohigh, and(ii) thepredominance ofaerobic prokaryotes andeukaryotes, except fora fewstations, inthewestern andsouthwestern sides ofthebay, as evidenced bythelarge amountsofmonounsaturated PLFA.Suchsignificant regional differences inmicrobial community structure ofthebayindicate shifts inmicrobial community structure. Microorganisms insediments are responsible formany biochemical transformations, including degradation ofrecalcitrant chemical compounds insediments whichconstitute thefinal repository formany chemicals. Itisimperative to understand thedistribution ofmicrobial populations, since theyplay an important roleinthemineralization oforganic matteranddegradation ofpollutants. Inrecent years,pollution-induced changes inbenthic microbial community structurehavebeenwidely recognized, butitisoften difficult to define orquantitatively describe microbial community structureinsediments becauseoftheselectivity ofculture conditions andquantitative release ofmicroorganisms from thesediment. Analysis ofbiomarker compounds, as a measureofviable microbial biomass, hasbeenproposed as an alternative methodtodetermine microbial community structure.Analysis oflipids, especially phospholipids, hasbeen ofgreatvaluetoquantitatively describe microbial community structure aswellasmicrobial biomass (47). Fatty acid analysis hasalsobeenextensively employed tocontribute to bacterial phylogenic andtaxonomic classification (25), and hencethefatty acidcomposition insediments provides a powerful discriminating tool toinvestigators (15). Phospholipid ester-linked fatty acids(PLFA)havebeen usedforthecharacterization ofmicrobial community structureinsediments. Theprokaryotic andmicroeukaryotic componentsinthemicrobial community were defined by