STUDY OF MARINE SULFATE-REDUCING BACTERIAL POPULATION USING FLUORESCENT IN-SITU HYBRIDIZATION METHOD DURING DECOMPOSING PROCESSES OF DETRITAL MATERIAL AND POLYPEPTON IN MICROCOSMS

Microcosm experiments were performed to know the dynamics of sulfate- reducing bacterial population and volatile fatty acids (VFA) during de composition of polypepton and detrital material in the surface sedimen ts from Tokyo Bay and Sagami Bay. Population of sulfate-reducing bacte ria were detected and counted through fluorescent in situ hybridizatio n with SRB probe which has wide specificity to sulfate-reducing bacter ial group, and with Desulfobacter probe which has narrow specificity o nly to genus Desulfobacter. In the microcosms of the Tokyo Bay sample, vibrioid (0.7-1.0 x 2-2.5 mu m) and rod (1.5-1.8 x 2.5-3.5 mu m) shap ed SRB were detected on day 3, SRB population changed to cocci (0.7-1. 0 mu m) and rod (1.5-1.8 x 2.5-3.5 mu m) shaped cells on day 8. These rod shaped SRB were hybridized also with Desulfobacter probe. The incr ease of Desulfobacter followed by the increase of utilized acetate. In the Sagami Bay sample, only rod shaped SRB (0.7-1.2 x 2.5-6 mu m) was detected on day 35. On day 100, cocci (2-3 mu m) and short rod (0.7-1 .2 x 1.7-2.2 mu m) shaped SRB were detected. No cell was hybridized wi th Desulfobacter probe. It was considered that there was the successio n of sulfate-reducing bacterial population during decomposition of det rital material in the surface sediments. The probe method would be hel pful to understand population changes of sulfate-reducing bacteria in the natural bacterial communities.