SUMMARY: Chlorate-resistant mutants of the denitrifying bacterium were generated by transposon Tn5 mutagenesis. One class was deficient in membrane-bound nitrate reductase activity but retained a periplasmic nitrate reductase activity. Using transposon marker rescue it was shown that in one such mutant, M-6, the transposon was inserted in the membrane-bound nitrate reductase β subunit structural gene (termed in order to be consistent with the nomenclature of the major nitrate reductase operon). The translated sequence (total of 106 amino acids) from around the point of transposon insertion showed approximately 90% amino acid identity with the β subunits of the nitrate reductases. Under anaerobic growth conditions M-6 overproduced the periplasmic nitrate reductase activity allowing anaerobic growth with nitrate as electron acceptor. A regulatory link was inferred between the presence of the membrane-bound nitrate reductase and expression of the periplasmic nitrate reductase. This is the first demonstration of full denitrification in an organism possessing only a periplasmic nitrate reductase.


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