GalE's Role in Lipopolysaccharide O-Antigen Synthesis and Environmental Stress Resistance in STEC O5

Shiga toxigenic Escherichia coli (STEC) is known to cause severe diarrhea and other gastrointestinal disorders in animals and humans. The galE gene encodes the galE protein, which acts as an essential catalyst required to convert UDP-galactose into UDP-glucose, and vital for exopolysaccharide synthesis. In this study, a knockout mutant of the STEC galE gene (ΔgalE) was constructed and the biological functions of galE were analyzed. Relative to the wild-type strain, O-antigen synthesis within the ΔgalE mutant changed and displayed distinct profiles via SDS-PAGE coupled with silver staining and Western blot analysis. Furthermore, this mutant showed a reduction in swimming motility, diminished biofilm formation, and reduced replication within macrophages. In the complement-killing assay, the membrane attack complex (MAC) was deposited in greater amounts on the ΔgalE-deficient strain relative to the wild-type strain, indicating a higher susceptibility of the ΔgalE strain toward complement-dependent lysis. However, the mutant manifested a more pronounced tolerance to extreme environments despite exhibiting comparable replication in a growth medium. These results indicate that galE plays a significant roles in O-antigen biosynthesis and contributes to STEC pathogenicity.