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

Abstract

SUMMARY:Desulphovibrio 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 CO2 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, CO2 and succinate in the molar ratio 3 malate → 2 succinate + 2CO2+ 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 + CO2 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 CO2 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 H2 quantitatively to succinate; crotonate, maleate or acetylene-dicarb-oxylate were not reduced; malate was reduced slowly. Hence the reaction sequence: succinate ⇌ fumarate ⇌ malate ⇌ lactate ⇌ pyruvate ⇌ acetate probably takes place in these bacteria: a reversible succinate ⇌ fumarate system may form a link between sulphate reduction and the oxidation of organic compounds or hydrogen.