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Chlorate-resistant mutants of the denitrifying bacterium Thiosphaera pantotropha 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 beta subunit structural gene (termed narH in order to be consistent with the nomenclature of the Escherichia coli 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 beta subunits of the E. coli 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.

Original publication




Journal article


J Gen Microbiol

Publication Date





3205 - 3214


Amino Acid Sequence, Anaerobiosis, Base Sequence, Cell Membrane, Chlorates, Chromatiaceae, DNA Transposable Elements, DNA, Bacterial, Drug Resistance, Microbial, Gene Expression, Genes, Bacterial, Molecular Sequence Data, Mutagenesis, Insertional, Nitrate Reductase, Nitrate Reductases, Sequence Homology, Amino Acid, Subcellular Fractions