Genetic organization and polymorphism of the guaA gene encoding the GMP synthetase in Lactobacillus rhamnosus

The guaA gene encoding GMP synthetase was cloned from a potential probiotic strain of Lactobacillus rhamnosus. DNA sequence and Northern blot analysis indicated that (i) guaA did not belong to an guaAB operonic structure, con versely to enteric bacteria, (ii) L. rhamnosus guaA seemed to be highly exp ressed, and (iii) genetic regulation might differ from Bacillus subtilis. M oreover, differences in the genetic organization of guaA allowed discrimina tion of some closely related L. rhamnosus strains, with a rapid screening b y PCR.