The glycosyltransferase WekM is involved in the lipopolysaccharide biosynthesis and environmental adaptation of avian pathogenic Escherichia coli

Abstract:

[Objective] To investigate the role of WekM, the O-antigen glycosyltransferase of avian pathogenic Escherichia coli (APEC) O₁, in lipopolysaccharide biosynthesis and environmental adaptation. [Methods] The wekM-deleted strain ΔwekM of APEC O₁ was constructed by Red homologous recombination, and then the complementary strain CΔwekM was constructed. The impacts of wekM on bacterial growth and motility were examined. The lipopolysaccharide (LPS) profile and reactivity with rabbit anti-O₁ serum of each strain were identified by silver staining and Western blotting. Real-time fluorescence quantitative PCR was conducted to determine the transcriptional levels of flagellum-related genes, and ethidium bromide was used to measure the bacterial cell membrane permeability. Finally, the drug sensitivity test was carried out to identify the bacterial susceptibility to antibiotics such as ciprofloxacin. [Results] The constructed ΔwekM and CΔwekM were verified by PCR amplification and DNA sequencing. Compared with the wild type, ΔwekM showed incomplete LPS profile and absence of some O-antigen bands. Western blotting results showed that ΔwekM did not react with the anti-O₁ serum, suggesting that the loss of WekM impaired the LPS production. The deletion of wekM reduced the swimming motility and did not impact the bacterial growth rate compared with the wild type. The transcription levels of flagellum-related genes such as flgC were down-regulated in ΔwekM. The results implied that the reduced motility of ΔwekM was caused by the decrease in flagellar production. In addition, ΔwekM demonstrated increased cell membrane permeability compared with the wild type (P<0.01), and ΔwekM improved bacterial sensitivity to 7 antibiotics including polymyxin. This result suggested that the adaptability of ΔwekM to the environment was inhibited due to the increased cell membrane permeability. [Conclusion] The deletion of wekM in APEC results in diminished swimming motility, increased antibiotic resistance, improved cell membrane permeability, and damaged LPS integrity. The findings lay a foundation for mining the role of wekM and enrich our understanding of the stress resistance mechanism of APEC.

Key words:avian pathogenic Escherichia coli O₁;lipopolysaccharide;O-antigen;glycosyltransferase;environmental adaptation