Evidence for the involvement of a genetic determinant controlling functional specificity of group VI B elements in the metabolism of N2 and NO3- in the blue-green alga Nostoc muscorum

Abstract

The parent N. muscorum is Mo-requiring for growth on N2 or NO3- as nitrogen source. W and Cr both are observed to competitively inhibit the function of Mo in growth on N2 and NO3- media in parent strain. Spontaneous mutants growing in the presence of W or Cr were isolated and when examined, found to be W- or Cr-requiring for growth with both N2 and NO3- as nitrogen source. The results of the characterization of the three strains with respect to mutation frequency, interaction among Mo, W and Cr in growth on N2 as nitrogen source, and requirement of W or Cr for NO3- inhibition of heterocyst formation in W- or Cr-requiring strain growing in NO3- medium, all suggest the operation of a single genetic determinant in specifying whether Mo, W or Cr (group VI B elements) is required for growth with both N2 and NO3- as nitrogen sources. They also further suggest that this single genetic determinant is common to nitrogenase and nitrate reductase. © 1978.