AlgU controls environmental stress adaptation, biofilm formation, motility, pyochelin synthesis and antagonism potential in Pseudomonas protegens SN15-2

Pseudomonas protegens is a typical plant-growth-promoting rhizobacterium that can serve as an agricultural biocontrol agent. The extracytoplasmic function (ECF) sigma factor AlgU is a global transcription regulator controlling stress adaption and virulence in Pseudomonas aeruginosa and Pseudomonas syringae. Meanwhile, the regulatory role of AlgU in the biocontrol ability of P.protegens has been poorly studied. In this study, deletion mutations of algU and its antagonist coding gene mucA were constructed to investigate the function of AlgU in P. protegens SN15-2 via phenotypic experiment and transcriptome sequencing analysis. On the basis of phenotypic analyses, it was concluded that the AlgU whose transcription was induced by osmotic stress and oxidative stress positively regulated biofilm formation and tolerance towards osmotic, heat, and oxidation stresses, while it negatively regulated motility, pyochelin synthesis, and the ability to inhibit pathogens. On the basis of the RNA-seq analysis, compared to the wild-type strain, 12 genes were significantly upregulated and 77 genes were significantly downregulated in Delta algU, while 407 genes were significantly upregulated and 279 genes were significantly downregulated in Delta mucA, indicating the involvement of AlgU in several cellular processes, mainly related to resistance, carbohydrate metabolism, membrane formation, alginate production, the type VI secretion system, flagella motility and pyochelin production. Our findings provide insights into the important role of AlgU of P.protegens in biocontrol, which is of value in improving the biocontrol ability of P.protegens.

Automated summary

In this study, the function of the AlgU gene in P. protegens SN15-2 was investigated using phenotype experiments and transcriptome sequencing analysis. The results showed that AlgU positively regulated biofilm formation and tolerance to osmotic, heat, and oxidation stresses, while negatively regulating motility, pyochelin synthesis, and pathogen inhibition ability. The RNA-seq analysis revealed the involvement of AlgU in various cellular processes, mainly related to resistance, carbohydrate metabolism, membrane formation, alginate production, the type VI secretion system, flagella motility, and pyochelin production. These findings provide insights into the important role of AlgU in P. protegens biocontrol, which can contribute to improving biocontrol ability.