Genetic and evolutionary analysis of mutations in the gusA gene that cause the absence of beta-glucuronidase activity in Escherichia coli O157:H7

J Infect Dis. 2001 Oct 1;184(7):918-21. doi: 10.1086/323154. Epub 2001 Aug 15.

Abstract

Escherichia coli serotype O157:H7 do not exhibit beta-glucuronidase (GUD) activity but carry the gusA gene (uidA) that encodes for GUD. In trans-complementation, the gusA gene cloned from the GUD-positive variant strain 493-89 effectively restored GUD activity in O157:H7 strain 35150. Comparison of gusA sequences from the GUD-negative 35150 strain to that of 493-89 revealed several base mutations, including a guanosine (G) dinucleotide insertion that caused a frameshift in the 35150 gusA gene and introduced a predicted premature termination codon. This explains the absence of GUD activity in O157:H7. A 35150 gusA construct from which the G-G insertion was deleted restored activity in GUD-negative O157:H7 transformants. The G-G insertion was present in all GUD-negative O157:H7 strains but was absent in their GUD-positive variants. The G-G insertion that produced the characteristic GUD-negative phenotype to O157:H7 strains appeared later than the other gusA mutations in the evolutionary emergence of O157:H7.

Publication types

  • Comparative Study

MeSH terms

  • Cloning, Molecular
  • Escherichia coli O157 / enzymology
  • Escherichia coli O157 / genetics*
  • Evolution, Molecular
  • Frameshift Mutation*
  • Genes, Bacterial*
  • Glucuronidase / deficiency
  • Glucuronidase / genetics*
  • Guanosine / genetics
  • Molecular Sequence Data
  • Mutagenesis, Insertional

Substances

  • Guanosine
  • Glucuronidase

Associated data

  • GENBANK/AF305917
  • GENBANK/AF305918