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Fakultät für Biologie, Chemie und Geowissenschaften

Ökologische Mikrobiologie - Prof. Tillmann Lüders

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Fröstl, JM; Seifritz, C; Drake, HL: Effect of nitrate on the autotrophic metabolism of the acetogens Clostridium thermoautotrophicum and Clostridium thermoaceticum, J. Bacteriology, 178, 4597-4603 (1996)
Abstract:
Although nitrate stimulated the capacity of Clostridium thermoautotrophicum and Clostridium thermoaceticum to oxidize (utilize) substrates under heterotrophic conditions, autotrophic H2-CO2-dependent growth was inhibited by nitrate. Under basal medium conditions, nitrate was also inhibitory to the use of one-carbon substrates (i.e., CO, formate, methanol, or the O-methyl groups of vanillate or syringate) as sole carbon-energy sources. This inhibitory effect of nitrate was by-passed when both O-methyl groups and CO were provided concomitantly; H2-CO2 did not replace CO. These results indicated that nitrate blocked the reduction of CO2 to the methyl- and carbonyl-levels. Based on the inability of acetogenic cells (i.e., cells cultivated without nitrate) to consume or reduce nitrate in resting cell assays, the capacity to dissimilate nitrate was not constitutive. Nitrate had no appreciable effect on the specific activities of enzymes central to the acetyl-CoA pathway. However, membranes obtained from cells cultivated under nitrate-dissimilating conditions were deficient in the b-type cytochrome that was typical of membranes from acetogenic cells, i.e., cells dependent upon the synthesis of acetate for the conservation of energy. Collectively, these findings indicated that (i) C. thermoautotrophicum and C. thermoaceticum cannot engage the carbon-fixing capacities of the acetyl-CoA pathway in the presence of nitrate, and (ii) the nitrate block on the acetyl-CoA pathway occurs via an alteration in electron transport.
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