Inhibition of growth of Bacillus thuringiensis by amino acids in defined media

The insect pathogen Bacillus thuringiensis var. thuringiensis grows well in a synthetic medium containing ammonia as the sole source of nitrogen. If certain nonrequired amino acids are added singly or in combination to a basal synthetic medium, growth is completely inhibited or severely limited. Amino acids giving this effect, grouped for experimental purposes, are valine/leucine/isoleucine and serine/methionine/threonine/glycine. Other strains of B. thuringiensis (varieties sotto, galleriae, and finitimus), as well as Bacillus cereus, react in a similar manner when inhibitory concentrations of valine, leucine, or isoleucine are added to a minimal medium. Mutants of the B. thuringiensis strain studied were isolated which were resistant to the growth inhibitory effects of these amino acids. Resistance to the growth inhibitory effect of one amino acid, however, did not always impart resistance to the others. The mutant resistant to isoleucine inhibition was found to be resistant to leucine and valine also, whereas growth of the leucine-resistant mutant was still inhibited by isoleucine. The strain resistant to valine was sensitive to inhibition by both leucine and isoleucine.