Diverse pathways for salicin utilization in Shigella sonnei and Escherichia coli carrying an impaired bgl operon.
Utilization of the aryl-β-glucosides salicin or arbutin in most wild-type strains of E. coli is achieved by a single-step mutational activation of the bgl operon. Shigella sonnei, a branch of the diverse E. coli strain tree, requires two sequential mutational steps for achieving salicin utilization as the bglB gene, encoding the phospho-β-glucosidase B, harbors an inactivating insertion. We show that in a natural isolate of S. sonnei, transcriptional activation of the gene SSO1595, encoding a phospho-β-glucosidase, enables salicin utilization with the permease function being provided by the activated bgl operon. SSO1595 is absent in most commensal strains of E. coli, but is present in extra-intestinal pathogens as bgcA, a component of the bgc operon that enables β-glucoside utilization at low temperature. Salicin utilization in an E. coli bglB laboratory strain also requires a two-step activation process leading to expression of BglF, the PTS-associated permease encoded by the bgl operon and AscB, the phospho-β-glucosidase B encoded by the silent asc operon. BglF function is needed since AscF is unable to transport β-glucosides as it lacks the IIA domain involved in phopho-relay. Activation of the asc operon in the Sal(+) mutant is by a promoter-up mutation and the activated operon is subject to induction. The pathway to achieve salicin utilization is therefore diverse in these two evolutionarily related organisms; however, both show cooperation between two silent genetic systems to achieve a new metabolic capability under selection.
Desai
Stuti K
SK
Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore, India.
Nandimath
Krithi
K
Mahadevan
S
S
D001104:Arbutin / Q000378:metabolism; D001592:Benzyl Alcohols / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial; D020868:Gene Silencing; D005798:Genes, Bacterial; D005960:Glucosides; D009154:Mutation; D009876:Operon; D012764:Shigella sonnei / Q000235:genetics / Q000378:metabolism*; D024363:Transcription Initiation Site; D015533:Transcriptional Activation
D001592:Benzyl Alcohols; D004269:DNA, Bacterial; D005960:Glucosides; C005696:salicin; D001104:Arbutin