A novel sulfate-reducing bacterium, strain Mb1PaT, was isolated from the sediments of a freshwater floodplain lake. Cells of strain Mb1PaT were rod-shaped, 1-1.3 microm wide and 2.6-3 microm long, motile and Gram-negative. The bacterium grew on straight-chain carboxylic acids with 4-17 carbon atoms. Electron donors with an even number of carbon atoms were oxidized to acetate and electron donors with an odd number of carbon atoms were oxidized to acetate and propionate. No other compounds were found to be used as electron donors. No growth occurred in the absence of sulfate. The optimum temperature for growth was between 25 and 30 degrees C and the maximum temperature for growth was 32 degrees C. Strain Mb1PaT grew very slowly in medium with 5 g NaCl l(-1) with optimum growth occurring with up to 1.0 g NaCl l(-1). Analysis of the 16S rRNA gene showed that strain Mb1PaT belonged to the delta-subclass of the Proteobacteria, was a member of the family Desulfobacteraceae, but lacked similarity with any currently described representatives. The combined phylogenetic analysis and physiological data indicate that strain Mb1PaT represents a new genus and the name Desulforegula conservatrix is proposed. The type strain is Mb1PaT (= DSM 13527T = ATCC BAA-134T).