SUMMARY: Four strains of Desulfovibrio each, excreted pyruvate to a constant level during growth; it was re-absorbed when the substrate (lactate) was exhausted. Malate, succinate, fumarate and malonate also accumulated during growth.

One of the strains (Hildenborough) excreted α-ketoglutarate as well as pyruvate when incubated in nitrogen-free medium; the former was re-absorbed on addition of NHCl. In a low-lactate nitrogen-free medium, strain Hildenborough rapidly re-absorbed the pyruvate initially excreted, but did not re-absorb the α-keto-glutarate. Arsenite (1 mM) prevented the accumulation of α-ketoglutarate; 1 mM-malonate did not affect the accumulation of keto acids.

Isocitrate dehydrogenase activity (NAD-specific) in all strains was lower than NADP-specific glutamate dehydrogenase activity. α-Ketoglutarate dehydrogenase could not be detected in any strain. NADPH oxidase activity was demonstrated.

This and previous work indicate that a tricarboxylic acid pathway from citrate to α-ketoglutarate exists in spp., and that succinate can be synthesized via malate and fumarate; however, an intact tricarboxylic acid cycle is evidently not present. The findings are compared with observations on biosynthetic pathways in Clostridia, obligate lithotrophs, phototrophs, and methylotrophs, and various facultative bacteria.


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