The metabolism of malate and certain other compounds by Desulphovibrio desulphuricans.

S U M M A R Y : Desulphowifio desulphuricans (strain El Agheila Z) oxidized malate, fumarate, succinate, lactate and pyruvate quantitatively to acetate in cultures containing excess sulphate. Polysaccharide accumulated in old cultures. Cell suspensions harvested from malate media yielded theoretical amounts of sulphide and CO, from malate, fumarate or succinate + excess sulphate. Succinate was formed transiently during malate oxidation. Various inorganic sulphur-containing anions, methylene blue or oxygen acted as alternative hydrogen acceptors to sulphate for malate oxidation. In the absence of sulphate, malate was metabolized yielding acetate, CO, and succinate in the molar ratio 3 malate+2 succinate + 2C0, + acetate ; in hydrogen, malate or fumarate were partly reduced to succinate. Malate or fumarate accelerated the reduction of sulphate, but not dithionite, in hydrogen. Suspensions treated with cetyltrimethylammonium bromide formed fumarate and lactate + CO, from malate. Fumarate was formed via a reversible fumarase ; lactate was formed via a decarboxylase system independent of cozymase, Mn++, cocarboxylase or codecarboxylase. Cell suspensions harvested from lactate media yielded theoretical amounts of sulphide and CO, from lactate or pyruvate+excess sulphate. In the presence of arsenite, pyruvate was formed from lactate ; pyruvate formation was demonstrated with another strain. Suspensions of strain California 43 : 63 harvested from lactate media reduced fumarate in H, quantitatively to succinate ; crotonate, maleate or acetylene-dicarb-oxylate were not reduced; malate was reduced slowly. Hence the reaction sequence : succinatesfumarate ~malate-+Iactate+pyruvate-t acetate probably takes place in these bacteria ; a reversible succinate Sfumarate system may form a link between sulphate reduction and the oxidation of organic compounds or hydrogen. Malate was the carbon source originally used by Beijerinck (1895) for the cultivation of sulphate-reducing bacteria, though lactate, introduced by his pupil van Delden (1903), has since been more widely used. There have been relatively few detailed studies of the metabolism of carbon compounds by sulphate-reducing bacteria, Baars (1930) examined the ability of many organic compounds to support growth of the bacteria and showed that acetate was usually an end product of carbon compound oxidation. Senez (1951) showed that pyruvate oxidation was accompanied by greater growth and less sulphide formation than was lactate oxidation, and Postgate (195%) showed that growth in the absence of sulphate could occur in pyruvate media, the ' sulphate-free ' metabolism giving CO,, acetate and ethanol among its products (Postgate, 19523). Subsequently, Sadana (1954) obtained an extract which converted pyruvate to ethanol …