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Calculation showed that rates of sulphate reduction by the Hildenborough strain of Desul/ovibrio vulgaris in non-nutrient buffer with gaseous hydrogen as electron donor were as high as, or higher than, the maximum possible rate of sulphate reduction during growth.
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I~espirometry showed that H~ oxidation was completely suppressed during growth unless the whole electron transport system was bypassed with a redox dye or the sulphate reductase system (terminal electron acceptor) was bypassed with FM_N.
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Growth experiments with intermittent sulphate feeds showed that cells under H~ "wasted" most of the sulphate by a reaction unconnected with growth, and thus made much less growth than did similar cultures under N 2.
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H~ exerted no discernible "lactate-sparing" action (that is, it did not serve as an alternative energy source) in low-lactate medium.
The results are discussed in relation to metallic corrosion by the sulphate-reducing bacteria.
The non-sporulating dissimilatory sulphate-reducing bacteria (De-8ul]ovibrio spp.) use sulphate and other sulphur-containing anions as terminal electron acceptors for energy-yielding reactions (Postgate, 1951 b); growth occurs on simple carbon-and-energy sources, principally organic acids, under gases such as H2 and N~ (see, e.g., MacPherson and Miller, 1963). Almost all strains hitherto isolated possess hydrogenase and are able to reduce sulphate quantitatively to sulphide by oxidation of gaseous hydrogen when suspended in non-nutrient buffer, according to the equation 4 H 2 + S04---+ 4 H20 + S-- Stephenson and Stickland, 1931).
Butlin et al. (1949) developed a medium for the growth of sulphatereducing bacteria, containing sodium lactate, sulphate and other inorganic salts, and yeast extract, and observed that growth from a small inoculum reached a maximum, as assessed visually, in about 48 h.
Postgate (1953), using a pure culture of the Hildenborough strain, obtained maximum cell densities of about 120 vg/dry weight/ml of this medium, and observed hydrogen absorption coefficients (__gL)sulphate~