title: Polynucleotide phosphorylase is required for Escherichia coli O157:H7 growth above refrigerated temperature.
abstract: BACKGROUND
  The growth of Escherichia coli O157:H7 in contaminated dairy and other refrigerated food products due to temperature fluctuation poses a major food safety threat. Effective control or inhibition of E. coli O157:H7 growth depends on our understanding of mechanisms that regulate its growth at low temperature. We hypothesized that polynucleotide phosphorylase (PNPase) plays a critical role in E. coli O157:H7 low-temperature growth.
  
  
  METHODS
  To test this hypothesis, the pnp deletion mutant of E. coli O157:H7 was generated using the λ Red recombinase system, and the growth and survival of wild-type and pnp deletion mutant strains were compared at low temperatures.
  
  
  RESULTS
  The growth of pnp deletion mutant strains in Luria Broth (LB) and agar plate at 37°C was similar to their corresponding wild-type strains, while the deletion of pnp impaired E. coli O157:H7 growth in LB at 10°C and 22°C; growth impairment could be partially recovered in the mutant strains by ectopic expression of the pnp complementation plasmid, demonstrating that growth impairment was PNPase-specific. During 14 days of 10°C storage in both LB and milk, wild type strain EDL933 grew and reached >8 log10 colony-forming units per milliliter after 4 days of 10°C storage, while EDL933Δpnp gradually died off with effects more pronounced in milk, which were again mitigated by pnp overexpression. In addition, pnp deletion impaired the motility of E. coli O157:H7 but did not affect its susceptibility to H2O2.
  
  
  CONCLUSIONS
  PNPase is required for the growth of E. coli O157:H7 at low temperature; PNPase thus provides a molecular target to control the growth of E. coli O157:H7, which may have important practical applications in dairy and other food industry.
authors: 1 School of Food Science, Washington State University , Pullman, Washington.
authors: Jia
authors: J
authors: Hu
authors: Richard J
authors: RJ
authors: McCormick
authors: Warrie J
authors: WJ
authors: Means
authors: Mei-Jun
authors: MJ
authors: Zhu
mesh_terms: D000818:Animals; D003080:Cold Temperature; D015169:Colony Count, Microbial; D019453:Escherichia coli O157 / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D005511:Food Handling; D005516:Food Microbiology; D005517:Foodborne Diseases / Q000382:microbiology*; D015964:Gene Expression Regulation, Bacterial; D005816:Genetic Complementation Test; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008892:Milk / Q000382:microbiology*; D009068:Movement; D011117:Polyribonucleotide Nucleotidyltransferase / Q000235:genetics* / Q000378:metabolism; D017384:Sequence Deletion
chemical_list: D029968:Escherichia coli Proteins; D006861:Hydrogen Peroxide; D011117:Polyribonucleotide Nucleotidyltransferase