Construction and complementation of the first auxotrophic mutant in the spirochaete Leptospira meyeri

In bacteria, the first reaction of the tryptophan biosynthetic pathway involves the conversion of chorismate and glutamine to anthranilate by the action of anthranilate synthase, which is composed of the alpha (trpE gene product) and beta (trpG gene product) subunits. In this study, the tryptophan biosynthetic gene trpE of the spirochaete Leptospira meyeri was interrupted by a kanamycin-resistance cassette by homologous recombination. The trpE double cross-over mutant was not able to grow on solid or in liquid EMJH medium. In contrast, the trpE mutant showed a wild-type phenotype when tryptophan or anthranilate was added to the media, therefore showing that disruption of the L. meyeri trpE gene resulted in tryptophan auxotrophy. The authors have also characterized a second selectable marker that allows the construction of a spectinomycin-resistant L. meyeri-E. coli shuttle vector and the functional complementation of the L. meyeri trpE mutant.