With three annotated b-galactosidase genes, Xanthomonas campestris cannot grow well using lactose as the sole carbon source. Previously, a lactose-utilizing strain (Xc17L) with elevated b-galactosidase activity was isolated by mutagenesis with nitrous acid. The gene (galD) responsible for the enzyme elevation was studied by Tn5 transposition of Xc17L, cloning of the wild-type gene, nucleotide sequence analysis, genetic complementation, and Western blotting. The results indicated that galD (1740-bp long with 65.7% G+C content, encoding a protein of 579 aa with a MW of 66) is indeed a novel b-galactosidase gene. Using the GalD sequence for blast, a new family of b-galactosidases from other organisms has been found.?
