A COMBINED ECOLOGICAL AND PHYSIOLOGICAL APPROACH TO STUDYING SULFATE REDUCTION WITHIN DEEP MARINE SEDIMENT LAYERS

Details of techniques and approaches for a comprehensive and integrate d study of bacteria in deep marine sediment layers are presented. The effectiveness of these techniques is documented by reference to anaero bic sulphate-reducing bacteria and their associated activity in deep s ediments from the Japan Sea and Peru Margin. The effect of sample stor age and pressure on the results obtained is considered. The characteri stics of enrichment cultures of sulphate-reducing bacteria demonstrate that they are metabolically diverse, and that this diversity is maint ained with increasing sediment depth. Pure cultures of sulphate-reduci ng bacteria from 80 and 500 m are barophilic. Maximum growth occurs at their calculated in situ pressure, which demonstrates their deep sea origin. These and other data [1-6] demonstrate the presence of a deep bacterial biosphere (to a depth of at least 500 m) within marine sedim ents, which is well adapted to this extreme environment. These techniq ues should be applicable to other subsurface environments where a comb ination of low bacterial populations and activities provide a major ch allenge to the study of microbial ecology.