ISOLATION OF SULFATE-REDUCING BACTERIA FROM DEEP SEDIMENT LAYERS OF THE PACIFIC-OCEAN

Bacterial populations exist at great depths in marine sediments bur li ttle is known about the type and characteristics of organisms in this unique bacterial environment Cascadia Margin sediments from the Pacifi c Ocean have deep bacterial activity and bacterial populations, which are stimulated around a gas hydrate zone (215-225 m below sea floor [m bsf]). Bacterial sulfate reduction is the dominant anaerobic process w ithin these sediments, and the depth distribution of sulfate-reducing activity corresponds with distributions of viable sulfate-reducing bac teria (SRB). Anaerobically scored sediments from this sire were used t o isolate sulfate-reducing bacteria using a temperature-gradient syste m, elevated pressure and temperatures, different media, and a range of growth substrates. A variety of enrichments on lactate were obtained from 0.5 and 222 mbsf; with surprisingly more rapid growth from the de eper sediments. The temperature range of enrichments producing strong growth from 222 mbsf was markedly wider than those from the near surfa ce sediment (15-45 degrees C and 9-19 degrees C, respectively). This p resumably reflects a temperature increase in deeper sediments. Only a few of these enrichments were successfully isolated due to very slow o r no growth on subculture, despite the use of a wide range of differen t media and growth conditions. Psychrophilic and mesophilic sulfate-re ducing isolates were obtained from 0.5 m depth. As the minimum growth temperature of the mesophile (probably a Desulfotomaculum sp.) was abo ve the in situ temperature of 3 degrees C, it must have been present i n the sediment as spores. A larger number of isolates (23) was obtaine d from 222 mbsf; and these barophilic SRB were closely related (based on 16S rRNA gene analysis), but not identical to, Desulfovibrio profun dus, recently isolated from deep sediments from the Japan Sea. Bacteri a related to D. profundus may be widespread in deep marine sediments.