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.
Hussain Alattas, Samuele Sala, Joseph Boctor et al.· International Journal of Mol...· 0 citations
Abstract Current understanding of genomic diversity within the halophilic genus Salinivibrio relies predominantly on draft genomes, with only seven complete genomes among the 62 publicly available. Previous pangenome analysis suggested a closed genomic structure while concluding that Salinivibrio lacks polyhydroxyalkanoate (PHA) degradation capacity despite possessing biosynthesis genes. Here, we present eight complete Salinivibrio genomes from Pearse Lakes (Rottnest Island, Western Australia) generated using Oxford Nanopore long-read sequencing, alongside re-analysis of 38 high-quality public genomes (≥90% completeness and ≤5% contamination cut-off). Pangenome analysis revealed a more open structure than previously reported, with a core genome comprising 25% of total gene clusters and an accessory genome accounting for 71%. Panstripe analysis demonstrated significant temporal signal in gene gain and loss events associated with phylogenetic branch length (core: P=1.72×10⁻⁴; tip: P=2.64×10⁻¹⁴). All 46 genomes contained complete PHA biosynthesis operons (phaB-phaA-phaP-phaC) with high sequence conservation under strong purifying selection (Z=30.30, P<0.001). In a genome that readily gains and loses genes, this conservation indicates that PHA synthesis is a maintained pathway, which is difficult to reconcile with a previous report that Salinivibrio lacks PHA degradation capacity. We therefore searched the genomes by Hidden Markov Model-based homology rather than standard annotation and identified seven putative depolymerases that form a single accessory cluster in 15% of strains, all previously annotated as 3-oxoadipate enol-lactonase-2. These candidates retained all catalytic residues characteristic of active depolymerases but are divergent from reference PHA depolymerases which could explain why annotation missed them. They remain putative and require biochemical confirmation. Both the expanded pangenome and these candidates emerged from standardized homology-based re-analysis, showing that annotation-dependent approaches can overlook genomic diversity and divergent enzyme families in non-model organisms. Together, these results establish Salinivibrio as a genomically dynamic genus with potential for halophilic bioplastic production.
Crystal E. Young, Harrison O'Sullivan, Hussain Alattas et al.· Microbial Genomics· 0 citations