CHARACTERIZATION OF MICROBIAL COMMUNITY STRUCTURE IN THE SURFACE SEDIMENT OF OSAKA BAY, JAPAN, BY PHOSPHOLIPID FATTY-ACID ANALYSIS

Twenty-eight sediment samples collected from Osaka Bay, Japan, were an alyzed for phospholipid ester-linked fatty acids (PLFA) to determine r egional differences in microbial community structure of the bay. The a bundance of three major groups of C-10 to C19 PLFA (saturated, branche d, and monounsaturated PLFA), which accounted for 84 to 97% of the tot al PLFA, indicated the predominance of prokaryotes in the sediment. Th e distribution of six clusters obtained by similarity analysis in the bay revealed a marked regional distribution in the PLFA profiles. Tota l PLFA concentrations (0.56 to 2.97 mug/g [dry weight] of the sediment ) in sediments also showed marked variation among the stations, with h igher concentrations of total PLFA in the central part of the bay. The biomass, calculated on the basis of total PLFA concentration, ranged from 0.25 x 10(8) to 1.35 x 10(8) cells per g (dry weight) of the sedi ment. The relative dominance of microbial groups in sediments was desc ribed by using the reported bacterial biomarker fatty acids. Very smal l amounts of the characteristic PLFA of microeukaryotes in sediments i ndicated the restricted distribution of microeukaryotes. By examining the distribution of clusters and groups of microorganisms in the bay, there were two characteristics of the distribution pattern: (i) the pr edominance of anaerobic bacteria and gram-positive prokaryotes, charac terized by the high proportions of branched PLFA in the eastern and no rtheastern sides of the bay, where the reported concentrations of poll utants were also high, and (ii) the predominance of aerobic prokaryote s and eukaryotes, except for a few stations, in the western and southw estern sides of the bay, as evidenced by the large amounts of monounsa turated PLFA. Such significant regional differences in microbial commu nity structure of the bay indicate shifts in microbial community struc ture.