ABSTRACT
Combined microautoradiography and fluorescence in situ hybridization (FISH) was used to investigate carbon metabolism in uncultured bacteria from the genus Achromatium. All of theAchromatium species identified in a freshwater sediment from Rydal Water, Cumbria, United Kingdom, which were distinguishable only by FISH, assimilated both [14C]bicarbonate and [14C]acetate. This extends previous findings thatAchromatium spp. present at another location could only utilize organic carbon sources. Achromatium spp., therefore, probably exhibit a range of physiologies, i.e., facultative chemolithoautotrophy, mixotrophy, and chemoorganoheterotrophy, similar to other large sulfur bacteria (e.g., Beggiatoa spp.).