Multiple-aminoglycoside-resistant mutants of Bacillus subtilis deficient in accumulation of kanamycin

Three classes of spontaneous multiple-aminoglycoside-resistant (mar) mutants of Bacillus subtilis were isolated by plating on a low (1.2 mug/ml) concentration of kanamycin sulfate and were found to be resistant also to low concentrations of paromomycin, neomycin and gentamicin. The three classes could be distinguished one from another by their degree of cytochrome deficiency, respiration deficiency, and susceptibility to kanamycin lethality. A fluctuation test showed that the mutations were spontaneous and not induced by the conditions of selection. Representative strains from two classes of mutants (mar-2 and mar-3) accumulated aminoglycoside very poorly in comparison with the parent strain, whereas a strain of the third class (mar-1) inactivated aminoglycoside present in the growth medium. The mar-3 strain studied (aroD163) had previously been shown to be a menaquinone auxotroph (Farrand and Taber, 1973) and to be deficient in amino acid uptake (Bisschop et al., 1975). Such mutants, which are resistant to low concentrations of aminoglycosides, may be of use in elucidating the biochemical and genetic bases of certain bacterial transport systems.