Duplication of the beta-galactosidase gene in some Lactobacillus plantarumstrains

Curing of a plasmid that encoded a beta-galactosidase gene (beta-gal) from the Lactobacillus plantarum strain of dairy origin LL441 was not accompanie d by complete loss of the lactose utilization phenotype. DNA-DNA hybridizat ion, using an internal fragment of the beta-gal gene as a probe, revealed a second determinant located on the chromosome of the cured derivatives. The chromosomal copy was present in all of a series of beta-Gal(+) L. plantaru m and Lactobacillus pentosus strains from different origins. In addition, f our other L. plantarum strains harboured plasmid encoded beta-gal genes as well. Since both sequence cross-hybridized and present a similar genetic or ganization, it is postulated that the plasmid copy was generated through ge ne duplication and, probably, selected by growth of the strains in lactose rich environments. (C) 1999 Elsevier Science B.V. All rights reserved.