A comparative study of the evolution of cellobiose utilization in Escherichia coli and Shigella sonnei.
The chb operon of Escherichia coli is involved in the utilization of chitooligosaccharides. While acquisition of two classes of mutations leading to altered regulation of the chb operon is necessary to confer the ability to utilize the glucose disaccharide cellobiose to wild-type strains of E. coli, in the closely related organism Shigella sonnei, Cel+mutants arise relatively faster, requiring only a single mutational event. In Type I mutants, the insertion of IS600 at -21 leads to ChbR regulator-independent, constitutive expression of the operon. In Type II mutants, the insertion of IS2/600 within the distal binding site of the negative regulator NagC leads to ChbR-dependent cellobiose-inducible expression of the operon. These studies underscore the significance of strain background, specifically the diversity of transposable elements, in the evolution of novel metabolic functions. Constitutive expression of the chb operon also enables utilization of the aromatic β-glucosides arbutin and salicin, implying that the chb structural genes are inherently promiscuous.
Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore, 560012, India.
Asha Mary
AM
Joseph
Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore, 560012, India.|Department of Pathology, Emory University School of Medicine, 615 Michael St, Atlanta, GA, 30322, USA.
Robert
R
Sonowal
Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bangalore, 560012, India. mahi@mrdg.iisc.ernet.in.
Subramony
S
Mahadevan
D001104:Arbutin / Q000378:metabolism; D001592:Benzyl Alcohols / Q000378:metabolism; D002475:Cellobiose / Q000378:metabolism*; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics; D019143:Evolution, Molecular; D005960:Glucosides / Q000378:metabolism; D009154:Mutation; D009876:Operon; D012097:Repressor Proteins / Q000235:genetics; D012764:Shigella sonnei / Q000235:genetics* / Q000378:metabolism
D001592:Benzyl Alcohols; D004251:DNA Transposable Elements; D029968:Escherichia coli Proteins; D005960:Glucosides; D012097:Repressor Proteins; C067862:nagC protein, E coli; D002475:Cellobiose; C005696:salicin; D001104:Arbutin
Cellobiose; IS elements; Shigella sonnei; chb operon