Resistance to amino acid inhibition in Caulobacter crescentus

Summary Growth of Caulobacter crescentus CB15 in minimal glucose-ammonium media is inhibited by nine L-amino acids: cysteine, histidine, isoleucine, leucine, methionine, phenylalanine, serine, threonine, and valine. Addition of 10 mM L-alanine prevents the inhibitory response. Several other amino acids also prevented the inhibitory response but to a lesser extent. Mutants resistant to amino acid inhibition designated Aar^-, were isolated and characterized. All mutants exhibited a phenotype of cross-resistance to all amino acids and most analogues, regardless of the selective agent. Representative mutations were linked 80% to cysB by RP4-mediated conjugation, and all mutations were linked 10–25% to cysB by transduction. Although the mechanism of amino acid inhibition is not known, the alanine protection and the Aar^- phenotype seem to be due to a reduced rate of uptake of inhibitory amino acids.