CLONING, SEQUENCING, AND CHARACTERIZATION OF A GENE (NART) ENCODING ATRANSPORT PROTEIN INVOLVED IN DISSIMILATORY NITRATE REDUCTION IN STAPHYLOCOCCUS-CARNOSUS

A Tn917 mutant of Staphylococcus carnosus TM300, nrIII, was isolated a nd characterized. Mutant nrIII did not take up nitrate or accumulate n itrite when grown in B-medium supplemented with up to 10 mM nitrate un der anoxic conditions; however, it displayed wild-type levels of benzy l Delta viologen-linked nitrate reductase activity, Cultivated in B-me dium with nitrate under oxic conditions, mutant nrIII accumulated five fold less nitrite than the wild-type. The mutation in S. carnosus mill could be complemented with a 2-kb chromosomal EcoRI-HpaI fragment fro m the wild-type. The gene affected by transposon insertion in mutant n rIII was cloned and sequenced. Analysis of the deduced amino acid sequ ence revealed that this gene, designated narT, encodes a highly hydrop hobic 42-kDa transmembrane protein of 388 amino acids and shows simila rities to transport proteins that play a role in nitrate import or nit rite export. The inability of nrIII to take up nitrate under anoxic co nditions and its ability to take up and accumulate nitrite in the pres ence of benzyl viologen, a nitrate ionophore, under the same condition s suggest that NarT represents a transport protein required for nitrat e uptake under anoxic conditions in S. carnosus.