Discovery and Comprehensive Characterization of Pseudomonas sp. MUP55: Taxonomy, Massetolide-Mediated Biocontrol, and Regulatory and Antimicrobial Contributions of the pvf Cluster
Pseudomonas sp. MUP55, isolated from rainfall water in Western Australia, was characterized by polyphasic taxonomy and functional assays. Whole-genome and 16S rRNA phylogeny placed Pseudomonas sp. MUP55 in the Pseudomonas fluorescens species group. Massetolide A/D was identified as the leading candidate bioactive compound(s), consistent with its biosynthetic gene cluster, GNPS library matching, and loss of activity in regulatory mutants. The strain showed broad-spectrum antimicrobial activity against bacterial (Escherichia coli and Xanthomonas campestris) and fungal (Fusarium oxysporum and Rhizoctonia solani) plant pathogens. GacA regulates Massetolide production: a P58L mutation abolished synthesis and reduced biocontrol efficacy. Metabolomic and transcriptomic analysis of a ΔpvfC mutant revealed that the pvf cluster regulates specialized metabolism while also contributing to secreted growth-inhibitory activity. The pvf cluster differentially regulates dual siderophore systems and uncouples the co-regulated small RNAs rsmY and rsmZ in the Gac/Rsm cascade. Deletion of pvfC partially reduced the growth-inhibitory activity of Pseudomonas sp. MUP55 supernatants against bacterial pathogens, indicating that pvfC also influences secreted antimicrobial activity beyond its global regulatory role. These findings establish Pseudomonas sp. MUP55 as a taxonomically novel, mechanistically characterized biocontrol agent with potential for sustainable agriculture.