DETECTION AND ENUMERATION OF MARINE SULFATE-REDUCING BACTERIA USING IN-SITU HYBRIDIZATION WITH 16S RIBOSOMAL-RNA OLIGONUCLEOTIDE PROBES

To obtain more basic and detail information on the ecology of marine s ulfate-reducing bacterial population, we studied the use of in situ hy bridization with 16S rRNA probes for their cellular level detection fr om natural environments. SRB probe was found to have wide specificity to sulfate-reducing bacterial groups. SRB probe hybridizes also with m ost species of delta-group of purple bacteria. However, most of them w ere found not to dominate in the coastal and estuarine environments. A lthough two species, Clostridium novyi and Myxococcus xanthus, have sa me sequences with SRB probe, they can be eliminated through observatio n under fluorescent microscope with having endospore and autofluoresce nce, respectively. Desulfobacter probe was found to be specific to gen us Desulfobacter. We modified dual staining method of Hicks ef al. (19 92) with SRB probe, and compared the numbers of sulfate-reducing bacte ria enumerated by the present method with conventional MPN method (med ium containing sodium lactate) using microcosm of zooplankton decompos ition. The numbers (4.5 x 10(6)-2.7 x 10(7)/ml) detected using in situ hybridization with SRB probe were about two orders of magnitude highe r than MPN method (1.1 x 10(3)-1.5 x 10(5)/ml).