Mining Microbial Niches: Sources of Bacteria for Enhancing Plant Growth and Resilience to pH, Salinity, Drought and Phytophthora infestans.

Enhancing plant resilience is crucial for sustainable agriculture and ecosystem health in an era of climate change and the global spread of plant pathogens. The strategic exploitation of diverse ecological niches to isolate microorganisms that promote plant growth, suppress pathogens and tolerate abiotic stress conditions is paramount. Here, 21 bacterial strains were isolated from three distinct sources: digestate produced from straw feedstock, Quercus ilex roots mycorrhised with Tuber aestivum, and a peperino stone fountain. These isolates were assigned to eight genera, Bacillus, Pseudomonas, Stenotrophomonas, Burkholderia, Acinetobacter, Aeromonas, Exiguobacterium and Sphingobacterium, all linked to plant growth promotion, stress mitigation and pathogen control. Tests for plant-growth-promoting and biocontrol activities included indole acetic acid, siderophores, hydrogen cyanide, cellulase and chitinase and phosphate/potassium solubilisation. Efficacy against Phytophthora infestans and tolerance to salinity, pH and drought were also assessed. Functional patterns varied by isolation source, suggesting niche-specific adaptation. Although all isolates displayed metabolic versatility, peperino stone strains exhibited higher tolerance to acidity and drought, while isolates from straw digestate and mycorrhizal roots tolerated alkalinity. Most isolates are promising for P. infestans control. These findings highlight the importance of targeted microbial sourcing in developing effective biofertilisers and biopesticides, offering sustainable solutions to agricultural and environmental challenges.