The effect of metal ions on the atypical mycobacteria: growth and colony coloration

Abstract

The effect of 30 metal ions on growth and colony color has been evaluated for 215 isolates of "atypical" mycobacteria and 5 isolates of Mycobacterium tuberculosis. Of the total number of ions tested, ten proved to have a variable effect on growth and eight induced specific changes in colony coloration. Although both effects could be generally related to the Runyon grouping system, neither procedure proved to be practical or specific for differential identification of individual species. Spectrophotometric analyses of acetone extracts were made from representative strains of "atypical" mycobacteria, grown in the presence (test) or absence (control) of metal ions, in an attempt to determine the chemical nature of metal ion induced color changes in colonies of these organisms. Induced colors were not extractable with organic solvents, indicating that these colors are not lipid associated. In all cases where applicable (chromogenic strains) the naturally occurring carotenoid pigments were found to be unaffected, in their spectral properties, by the presence of metal ions even though the natural yellow color was frequently masked by the ion induced colors. The close association of metal ion induced colors with acetone nonextractable cell components suggests the presence of reduced metal ions or the formation of metal hydroxides. The apparent presence of several metal ion reductase systems and their physiological implications are discussed.