The β-glucoside genes of Klebsiella aerogenes: conservation and divergence in relation to the cryptic bgl genes of Escherichia coli

The ability to metabolize aromatic β-glucosides such as salicin and arbutin varies among members of the Enterobacteriaceae. The ability of Escherichia coli to degrade salicin and arbutin appears to be cryptic, subject to activation of the bgl genes, whereas many members of the Klebsiella genus can metabolize these sugars. We have examined the genetic basis for β-glucoside utilization in Klebsiella aerogenes. The Klebsiella equivalents of bglG, bglB and bglR have been cloned using the genome sequence database of Klebsiella pneumoniae. Nucleotide sequencing shows that the K. aerogenes bgl genes show substantial similarities to the E. coli counterparts. The K. aerogenes bgl genes in multiple copies can also complement E. coli mutants deficient in bglG encoding the antiterminator and bglB encoding the phospho-β-glucosidase, suggesting that they are functional homologues. The regulatory region bglR of K. aerogenes shows a high degree of similarity of the sequences involved in BglG-mediated regulation. Interestingly, the regions corresponding to the negative elements present in the E. coli regulatory region show substantial divergence in K. aerogenes. The possible evolutionary implications of the results are discussed.