Comparative genomic analysis reveals reduced pathogenicity of Ralstonia spp. in water

Ralstonia spp., known for their adaptability across various habitats, are known to cause infections. The adaptive metabolic diversity of those inhabiting aquatic ecosystems remains poorly understood. We report four new Ralstonia pickettii genomes enriched in the cyanobacterial culture derived from bloom-forming cyanobacteria, Dolichospermum . A total of 228 complete genomes from the Ralstonia genus were utilized for phylogenetic inference, categorizing them based on isolation environment and host: water, soil, plant, and human groups. Meanwhile, the abundance of carbohydrate-active enzymes and secondary metabolites in water and human groups differed from the plant-host associate habitat. CeoB and two β-lactamases types of OXA were identified in the water habitat, showing similarities to certain strains in the human-host but differences from other habitats. The infectivity within water habitats seems to diminish, as evidenced by the decreased abundance of T3SS virulence proteins. Moreover, a distinctive pyrimidine degradation pathway in water degrades exogenous pyrimidines to supply nitrogen and other compounds for energy metabolism to provide a potential for broader habitat adaptability. Fluorescence in situ hybridization results confirmed that R. pickettii rarely attached to cyanobacterial cells, indicating that they are not parasitic relationships. We postulate that the absence of T3SS and the unique metabolic profile represent adaptations of Ralstonia to an aquatic free-living lifestyle.