AROMATIC HYDROCARBON-DEGRADING BACTERIA IN THE PETROLEUM-RICH SEDIMENTS OF THE GUAYMAS BASIN HYDROTHERMAL VENT SITE - PREFERENCE FOR AROMATIC CARBOXYLIC-ACIDS

Hydrocarbon-degrading bacteria in freshly collected petroleum-rich Gua ymas Basin sediments were enumerated on mineral base media separately containing naphthalene, biphenyl, or the aromatic carboxylic acids ben zoate, p-hydroxy-benzoate, mandelate, salicylate, phenylacetate, phtha late, or hydrocinnamate. The total numbers of bacteria were about 2 or ders of magnitude higher on the carboxylic acid media than on the two aromatic hydrocarbons, averaging 10(5) versus 10(3) bacteria per gram of sediment. Of 151 isolates of aerobic, mesophilic marine bacteria, 1 24 grew exclusively on one or more of the aromatic carboxylic acids. T he remaining 27 isolates used either naphthalene, biphenyl dibenzofura n, toluene, or phenanthrene and various combinations of aromatic carbo xylic acids. A similarity analysis of 135 of the isolates on the basis of substrate use, sodium chloride requirement, and growth on complex organic marine media identified 91 metabolically different bacterial s trains: 21 belonging to the group of aromatic hydrocarbon utilizers an d 70 to the group of carboxylic acid utilizers. Since compounds utiliz ed by organisms of the first group represent end products of petroleum catagenesis, we expected these organisms to predominate. Our results indicate, however, that in Guaymas Basin sediments the majority of hyd rocarbon-degrading bacteria, numerically and metabolically, appear to be determined by the presence of significant quantities of aromatic ca rboxylic acids.