Genetic and evolutionary analysis of mutations in the gusA gene that cause the absence of beta-glucuronidase activity in Escherichia coli O157:H7.
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.
Monday
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Division of Microbiological Studies, Food and Drug Administration, Washington, DC 20204, USA. smonday@cfsan.fda.gov
Whittam
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Feng
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D003001:Cloning, Molecular; D019453:Escherichia coli O157 / Q000201:enzymology / Q000235:genetics*; D019143:Evolution, Molecular; D016368:Frameshift Mutation; D005798:Genes, Bacterial; D005966:Glucuronidase / Q000172:deficiency / Q000235:genetics*; D006151:Guanosine / Q000235:genetics; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional
D006151:Guanosine; D005966:Glucuronidase