Microcalorimetric studies of the growth of sulfate-reducing bacteria: energetics of Desulfovibrio vulgaris growth.

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Abstract
The metabolism of D. vulgaris Hildenborough grown on medium containing lactate or pyruvate plus a high concentration of sulfate (36 mM) was studied. Molecular growth yields were 6.7 .+-. 1.3 and 10.1 .+-. 1.7 g/mol for Tactate and pyruvate, respectively. Under conditions in which the energy source was the sole growth-limiting factor, the formation of 0.5 mol of H2/mol of lactate and 0.1 mol of H2/mol of pyruvate were observed. The determination of metabolic end-products revealed that D. vulgaris produced, in addition to normal end-products (acetic acid, Co2 H2S) and H2, 2 and 5% of ethanol/mol of lactate and pyruvate, respectively. Power-time curves of growth of D. vulgaris on lactate and pyruvate were obtained by the microcalorimetric Tian-Calvet apparatus. The enthalpies, DHmet, associated with the oxidation of these substrates and calculated from growth thermograms were -36.36 .+-. 5 and -70.22 .+-. 3 KJ/mol of lactate and pyruvate, respectively. These experimental values were in agreement with the homologous values assessed from the theoretical equations of D. vulgaris metabolism of both lactate and pyruvate. The hydrogen production by this sulfate reducer constitutes an efficient regulatory system of electrons, from energy source through the pathway of sulfate reduction. This hydrogen value may facilitate interactions between this strain and other environmental microflora, especially metagenic bacteria.