Genomic and phenotypic characterization of Antarctic Pseudomonas/Aquipseudomonas sp. strains with cold-active antifungal activity against Botrytis cinerea.

Gray mold, caused by the psychrophilic necrotroph Botrytis cinerea, is a leading cause of postharvest losses, and its control is increasingly compromised by the spread of fungicide-resistant field populations and by the failure of conventional biocontrol agents to operate at cold-chain temperatures. Antarctic soils are a rational yet underexploited source of cold-active antagonists. Here we isolated cultivable bacteria from the rhizosphere of Deschampsia antarctica (King George Island) and screened them against B. cinerea at 22 °C and 0 °C. Of 57 bacterial isolates, 44 antagonized the pathogen at 22 °C but only 28 retained activity at 0 °C. Five isolates with indistinguishable rep-PCR fingerprints of the genus Pseudomonas (Pseudomonas fluorescens group) inhibited mycelial growth by ≥70% at low temperature and were equally effective against fenhexamid-resistant and multidrug-resistant strains, whereas the mesophilic references Bacillus subtilis and Bacillus amyloliquefaciens lost all activity at 0 °C. Polyphasic and genome-based characterization of the representative strain AN3A02 placed it within the recently proposed genus Aquipseudomonas (GTDB-Tk) and identified it as a putative novel species (ANI 94.89% and dDDH 57.9% against the closest type strain, P. Yamanorum). Genome mining predicted 10 biosynthetic gene clusters consistent with a multifactorial antagonism combining lipopeptides, high-affinity siderophores and volatile compounds. In contact-free assays, AN3A02 volatiles suppressed mycelial growth and the formation of resistance and reproductive structures at 0 °C and, on inoculated blueberries and table grapes stored under simulated cold-chain conditions, reduced gray-mold incidence below the level achieved by AN SO₂ emitter. These cold-adapted Antarctic Pseudomonas/Aquipseudomonas strains are promising candidates for the biological control of fungicide-resistant gray mold along the fruit cold chain.