Transformation of Streptomycin Markers in Rough Strains of Rhzzobzum Lupznz

RECENTLY, streptomycin dependence and resistance in bacteria have come to be viewed as accommodations requiring or permitting certain alterations by streptomycin of the expression of other genetic traits carried by the organism (e.g., GORINI 1964). For future evaluation of this viewpoint, it would be useful to have information about the relation of genetic factors governing dependence, resistance and sensitivity in a number of different species. The present article describes some analyses of these factors in a rough mutant of the plant symbiont Rhizobium Zupini. In these bacteria genetic transformation by DNA has been accomplished (BALASSA 1957), and streptomycin resistance and dependence (BALASSA and GABOR, 1961, 1965) were among the characters which have been transferred. When streptomycin dependent (str-d) strains served as donor (DNA source) to homologous streptomycin sensitive (str-s) recipients, transformation occurred at very low frequencies. All transformants were dependent on streptomycin and most of them at levels similar to that of the donor. A heterologous str-d donor produced still fewer transformants, partly dependent and partly resistant (str-r) , at a variety of different streptomycin levels (BALASSA and GABOR 1965). These findings suggest a linkage and a possible overlap between the determinants stP and str'. It seemed desirable to investigate further the relation between these markers and that for sensitivity, particularly by studying the back-transformation of a str-d strain and its derivatives. One can ask, for example, whether streptomycin dependent strains carry genetic factors for resistance, and to what extent factors for dependence are or can be suppressed to give lowered resistance or sensitivity.