DEGRADATIVE CAPACITIES AND 16S RIBOSOMAL-RNA-TARGETED WHOLE-CELL HYBRIDIZATION OF SULFATE-REDUCING BACTERIA IN AN ANAEROBIC ENRICHMENT CULTURE UTILIZING ALKYLBENZENES FROM CRUDE-OIL

A mesophilic sulfate-reducing enrichment culture growing anaerobically on crude oil was used as a model system to study which nutritional ty pes of sulfate-reducing bacteria may develop on original petroleum con stituents in oil wells, tanks, and pipelines, Chemical analysis of oil hydrocarbons during growth revealed depletion of toluene and o-xylene within 1 month and of m-xylene, o-ethyltoluene, m-ethyltoluene, m-pro pyltoluene, and m-isopropyltoluene within approximately 2 months, In a naerobic counting series, the highest numbers of CFU (6 x 10(6) to 8 x 10(6) CFU ml(-1)) were obtained with toluene and benzoate, Almost the same numbers were obtained with lactate, a substrate often used for d etection of the vibrio-shaped, incompletely oxidizing Desulfovibrio sp , In the present study, however, lactate yielded mostly colonies of ov al to rod-shaped, completely oxidizing, sulfate-reducing bacteria whic h were able to grow slowly on toluene or crude oil, Desulfovibrio spec ies were detected only at low numbers (3 x 10(5) CFU ml(-1)), In agree ment,with this finding, a fluorescently labeled, 16S rRNA-targeted oli gonucleotide probe described in the literature as specific for members of the Desulfovibrionaceae (suggested family) hybridized only with a small portion (< 5%) of the cells in the enrichment culture, These res ults are consistent with the observation that known Desulfovibrio spec ies do not utilize aromatic hydrocarbons, the predominant substrates i n the enrichment culture, All known sulfate-reducing bacteria which ut ilize aromatic compounds belong to a separate branch, the Desulfobacte riaceae (suggested family), Most members of this family are complete o xidizers, For specific hybridization with members of this branch, the probe had to be modified by a nucleotide exchange, Indeed, this modifi ed probe hybridized with more than 95% of the cells in the enrichment culture. The results show that completely oxidizing, alkylbenzene-util izing sulfate-reducing bacteria rather than Desulfovibrio species have to be considered in attempts to understand the microbiology of sulfid e production in oil wells, tanks, and pipelines when no electron donor s other than the indigenous oil constituents are available.