Anaerobic enrichment cultures with 2,3-dihydroxybenzoate as sole source of energy and organic carbon yielded slow-growing cultures of fermenting bacteria. A culture derived from a marine inoculum, strain Pe23DHB, consisted of two morphotypes: spirilloid, highly motile bacteria (the predominant type), and very few long, rod-shaped bacteria. The culture was able to grow by decarboxylation of 2,3-dihydroxybenzoate to catechol. The decarboxylating activity was localized mainly in the cytosol; addition of avidin or of sodium salts had no effect on the decarboxylating activity in cell-free extracts. These results suggest that strain Pe23DHB did not conserve energy by a membrane-bound biotin-containing decarboxylase, creating a Na+-gradient across the cytoplasmic membrane. The energy conservation mechanism remains unknown at present.