Altération par mutation de la régulation de la biosynthèse des cytochromes par les cultures anaérobies d'une bactérie anaérobie facultative

Abstract

Starting with a wild strain of Hafnia having the phenotype: nitrate reductase A +, nitrate reductase B +, chlorate reductase C +, tetrathionate reductase +, fumarate reductase +, hydrogen lyase +, we have isolated two kinds of mutants having the following phenotypes: (1) A –, B +, C +, tetrathionate reductase +, fumarate reductase +, hydrogen lyase +; (2) A –, B –, C –, tetrathionate reductase –, fumarate reductase +, hydrogen lyase –. The wild strain and the mutants of category 1 can use nitrate, nitrite, fumarate, and tetrathionate as hydrogen acceptors under anaerobic conditions. The mutants of category 2 can also reduce nitrite and fumarate, but cannot use nitrate and tetrathionate as hydrogen acceptors.We have studied the effects of nitrate, nitrite, fumarate, and tetrathionate on the biosynthesis of cytochromes a2, b1, b‐562, and c‐550 using anaerobic cultures of the wild strain and several mutants of the above two categories. The following observations were made: (a) Wild strain. Neither tetrathionate nor fumarate have any effect. Nitrate, on the other hand, markedly reduces the levels of cytochromes a2, b‐562, and c‐550. As for nitrite, it causes a decrease in levels of cytochromes b‐562 and b1, but a strong increase in that of cytochrome c‐550. It is as though nitrate abolishes the effects of nitrite on the biosynthesis of cytochromes b1 and c‐550. (b) Mutants of category 1. Nitrate causes the cytochrome a2 band to disappear, but does not influence the biosynthesis of cytochromes b‐562 and c‐550. Apart from the effect of nitrate on the formation of cytochrome a2, the different hydrogen acceptors caused no detectable spectral changes. (c) Mutants of category 2. We obtain essentially the same spectra as with the wild strain except when the cultures are nitrite‐grown. In this case, nitrite has the same effect as nitrate because it represses the biosynthesis of cytochrome c‐550.It is clear from this work that the two mutant phenotypes studied have profound and different effects in their regulation of the biosynthesis of cytochromes.