South Pacific Ocean

航海番号: KH-88-1 ; 航海日程: January 22 - March 25, 198

Heterotrophic bacterial flora of the Antarctic Ocean

Vertical distribution of heterotrophic bacteria was surveyed at six sampling stations in the Antarctic and the Indian Oceans. Seawater samples were collected at various water depths, ranging from 0 to 2000m. Total bacterial counts were determined by the direct microscopic method. Plate counts were carried out by the surface spreading method and the filter method using ORI agar medium. At a sampling station in the Antarctic Ocean, the enumeration of oligotrophic bacteria was also made using an MPN method. The total bacterial counts per ml of seawater in the Antarctic region ranged from (10)^4 to (10)^5,whereas the plate counts by the filter method were (10)^0 to (10)^1 at the upper 500m layers and (10)^ to (10)^0 at the deeper water lyers. The plate counts at 2℃ incubation temperature were higher than those at 20℃ by 1-2 orders of magnitude for the samples at stations in the Antarctic region. In contrast, the 20℃ counts for seawater from the Indian Ocean were slightly higher than 2℃ counts. The surface spreading method gave bacterial counts that were one order of magnitude higher than the filter method, and the counts with the MPN method using diluted medium were greater still, reaching about 10% of total bacterial counts. The results suggested that a fairly large proportion of the bacterial population in Antarctic seawater is in the actively growing state. More than 87% of the bacterial strains isolated from surface water of the Antarctic Ocean were orange- and yellow-pigmented bacteria. Among the pigmented bacteria, Gram-negative, non-motile, orange-pigmented rods that appeared to constitute a single species belonging to Flavobacterium-Cytophaga predominated

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 analyzed for phospholipid ester-linked fatty acids (PLFA) to determine regional differences in microbial community structure of the bay. The abundance of three major groups of C(10) to C(19) PLFA (saturated, branched, and monounsaturated PLFA), which accounted for 84 to 97% of the total PLFA, indicated the predominance of prokaryotes in the sediment. The distribution of six clusters obtained by similarity analysis in the bay revealed a marked regional distribution in the PLFA profiles. Total PLFA concentrations (0.56 to 2.97 μg/g [dry weight] of the sediment) in sediments also showed marked variation among the stations, with higher 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 × 10(8) to 1.35 × 10(8) cells per g (dry weight) of the sediment. The relative dominance of microbial groups in sediments was described by using the reported bacterial biomarker fatty acids. Very small amounts of the characteristic PLFA of microeukaryotes in sediments indicated 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 predominance of anaerobic bacteria and gram-positive prokaryotes, characterized by the high proportions of branched PLFA in the eastern and northeastern sides of the bay, where the reported concentrations of pollutants were also high, and (ii) the predominance of aerobic prokaryotes and eukaryotes, except for a few stations, in the western and southwestern sides of the bay, as evidenced by the large amounts of monounsaturated PLFA. Such significant regional differences in microbial community structure of the bay indicate shifts in microbial community structure