Metabolic Characteristics of Denitrification by Paracoccus denitrificans

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The environmental parameters affecting denitrification by Paracoccus denitrificans were investigated.Optimal pH was between 7.0 and 8.5,and optimal temperature between 30℃ and 40℃. The rate of denitrification could be enhanced by adding a small amount of yeast extract, 1 g/l, to the medium. The maximum spedific rate of nitrogen gas evolution was 160 mg N_2/g cell・hr for nitrate reduction and 120 mg N_2/g cell・hr for nitrite reduction. The above values were approximately two times higher than those found by Picinoty and Ornano, [Biochim. Biophys. Acta, 52,386 (1961)] and Chang and Morris [J. Gen. Microbiol., 29,301 (1962)] for P. denitrificans. The rate of nitrate reduction was almost constant irrespective of nitrate concentration, except at very low concentrations. On the other hand, the rate of nitrite reduction decreased at nitrite concentrations higher than 0.4g/l, i.e. inhibition by excess substrate was observed.Nitrite reduction was slower than nitrate reduction in the nitrate-reducing system of P. denitrificans, so that the concentration of nitrite accumulated as an intermediate in the medium peaked, and then decreased as nitrogen gas was evolved. This result suggested that nitrite reduction limited the overall rate of reaction of the successive reduction from nitrate to molecular nitrogen.The following stoichiometric equation for the denitrification, based on the data of the cellular elements and the yield coefficients, was proposed : For nitrate reduction, 0.4 C_6H_<12>O_6+NO_3^-+H^+→0.16 C_5H_8O_2N+0.42 N_2+1.6 CO_2+1.88 H_2O and for nitrite reduction, 0.24 C_6H_<12>O_6+NO_2^-+H^+→0.1 C_5H_8O_2N+0.45 N_2+0.94 CO_2+1.36 H_2O
公益社団法人日本生物工学会の論文
1978-06-25

Metabolic Characteristics of Denitrification by Paracoccus denitrificans

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