Mariemma Ortega de López2026-03-222026-03-221999http://epublica.saber.ula.ve/index.php/medula/article/download/5660/5463https://andeanlibrary.org/handle/123456789/63796The methods to isolate and to identify defective mutants in the nitrate anaerobic respiration (Nit-) tend to be preferential for certain mutated genes. This work presents a method denominated TNC, based in a modification of Fimmel and Haddock published in1979, but with highest advantages: it was not necessary to incubate with strict anaerobiosis, permitted both to amplify the spectre of mutated genes (including mol y fnr) and to detect very quickly the appearing red colonies, in only 24 hours of growth. Using it comparatively with the method of selection for chlorate resistance, the frequency of Nit- mutants and the distribution of genes mutated were higher. The TNC showed to be very sensitive and with reproducibility to identify differently Nit- mutants (TNC+) and Nit+ wild type (TNC-) clones; furthermore, it was efficient for the characterisation of bacteria strains and the genetic analysis. In the present work it was also established and evaluated a criteria of physiologic classification for preliminary grouping pleiotropic Nit- Gas- mutants in four genotypic subclass, by observing that moe mutations could be reverted phenotypically in late form with molybdate.esMutantBiologyGeneGeneticsarticle