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Linkage and Segregation of Unselected Markers in Matings of Nocardia erythropolis with Nocardia canicruria

Department of Microbiology, School of Medicine, University of South Dakota, Vermillion, South Dakota 57069

ABSTRACT

The segregation of unselected genes expressing resistance or susceptibility to acriflavine, erythromycin, streptomycin, and tetracycline was analyzed in selected prototrophic recombinants resulting from matings of Nocardia erythropolis and N. canicruria. The organisms were shown to be functionally haploid and appeared to contain not more than one genome. It was postulated that all observed genes were present in a linear linkage group. The ordering of the genes in N. erythropolis was: tetB10 eryB9 his-3 purA1 acr-2 strA1 (respectively, resistance to tetracycline and erythromycin, deficiency for histidine and for purine, and resistance to acriflavine and streptomycin). The ordering of the genes in N. canicruria was: purB2 tetA9 eryA7 acr-11 strB2 (respectively, deficiency for purine, and resistance to tetracycline, erythromycin, acriflavine, and streptomycin). Excluding the genes for acriflavine resistance, acr-2 and acr-11, resistance loci in N. erythropolis were not allelic to and showed lateral displacement from genes controlling phenotypically similar resistance in N. canicruria. Evidence for some lack of homology between N. erythropolis and N. canicruria genomes was found. Recombination phenomena between the nocardial species was postulated to occur as a result of formation of a heterogenomic zygote in which new combinations were produced. Production of selectable, haploid recombinants was ascribed to subsequent haploidization of the zygote.