ISOLATION OF A CITROBACTER SPECIES ABLE TO GROW ON MALONATE UNDER STRICTLY ANAEROBIC CONDITIONS

An anaerobic enrichment from lake mud yielded a pure culture of a facultatively anaerobic bacterium able to grow on malonate under strictly anaerobic conditions. Strain 16mal1 was identified as a member of the family Enterobacteriaceae, and assigned to the genus Citrobacter on the basis of morphological, metabolic and biochemical characteristics. Malonate was fermented under strictly anaerobic (sulphide-reduced) conditions to acetate and CO2 concomitant with growth. A maximum growth rate of 1.88 generations h-1 (μ = 1.30 h-1) was measured. The dry weight yield of cells from malonate was estimated at 2.5 g mol-1. Yeast extract was required for growth on malonate: other additives, or a vitamin source, could not replace this requirement. Other dicarboxylic acids were not degraded in the absence or presence of malonate. Malonate was degraded under anaerobic, but not aerobic conditions. Malonate-decarboxylating activity was inducible by malonate under both anaerobic and aerobic conditions. Malonate-decarboxylating activity was inducible by malonate under both anaerobic and aerobic conditions, and was not expressed in glucose- or citrate-grown anaerobic cultures. Monensin had no effect on malonate degradation, while 2,4-dinitrophenol decreased the rate of malonate degradation. This, with the lack of a sodium requirement for anaerobic growth on malonate, suggested that ATP generation may not be mediated by a sodium-pumping mechanism.