Effects of galU on bacterial physiology and responses to surfactants and antibiotics in Pseudomonas nitroreducens TX1

Pseudomonas nitroreducens TX1, a Gram-negative bacterium isolated from surfactant-contaminated environments, can utilize octylphenol polyethoxylates (OPEOn) as sole carbon source to grow, making it a promising candidate for bioremediation. One of the transposon insertion mutants exhibited impaired growth on OPEOn was identified as the galU mutant. The galU gene encodes UDP-glucose pyrophosphorylase, which are essential for lipopolysaccharide (LPS) and exopolysaccharide (EPS) biosynthesis. This study investigates the effects of galU in bacterial physiology. The galU deletion mutant exhibited impaired growth on OPEOn, and exhibited higher viability in succinate medium. The mutation also affected cell surface properties, which includes the changes of morphology and cell surface hydrophobicity. Morphological analyses by scanning electron microscopy revealed shortened cells, and altered cell surface roughness of galU mutant. The analyses of cell surface hydrophobicity, revealing the mutant exhibited lower cell surface hydrophobicity during the log phase. The stress resistance of galU mutant were also conducted. Biofilm formation was found to be increased in galU mutant, and antibiotic susceptibility tests showed that this mutant had increased resistance to multiple antibiotics, highlighting the critical role of LPS in maintaining membrane permeability and susceptibility in Pseudomonas species. Complementation of the galU mutation restored the phenotypes in terms of growth, morphology, and cell surface properties. These findings enhanced our understanding of galU by using its in-frame deletion mutant. The effects on bacterial physiology shown the potential for improving biodegradation of nonionic surfactants controlling biofilms and applying on antibiotics development.