Isolation and identification of antarctic microorganisms with activity against Pseudomonas aeruginosa and characterization of their antibacterial mechanism

Pseudomonas aeruginosa (PA) is a highly pathogenic and multidrug-resistant bacterium and a common cause of nosocomial infections. Therefore, safe and effective as well as preventive and therapeutic approaches are urgently needed. In this study, a strain named TJ31, which was isolated from sediment samples collected from Antarctic Lake Tuan Jie, demonstrated notable antibacterial activity against PA and was subsequently identified as Bacillus velezensis . To maximize the antibacterial activity of TJ31, single-factor experiments and response surface methodology were used to determine the optimal medium and fermentation conditions for this strain. Subsequently, a series of experiments were conducted to investigate the antibacterial mechanism of the TJ31 crude extract. The alkaline protease (AKP) assay and protein leakage assay demonstrated that the crude extract effectively disrupted the cellular integrity of PA, so that a finding was further corroborated by scanning electron microscopy (SEM) analysis. TJ31 crude extract inhibited respiratory chain dehydrogenase in PA, reduced the membrane potential of PA cells, and impaired bacterial viability. Furthermore, the crude extract suppressed the expression of virulence-associated genes, impeded twitching motility, impaired biofilm formation, reduced PA pyocyanin synthesis, and lowered PA pathogenic potential.