Functional Analyses of a Rhodobium marinum RH-AZ Genome and Its Application for Promoting the Growth of Rice Under Saline Stress.

Soil salinity stands among the most critical abiotic stressors, imposing severe limitations on global rice cultivation. Emerging evidence highlights the potential of beneficial microorganisms to enhance crop salt tolerance. In this study, a halotolerant bacterial strain, Rhodobium marinum RH-AZ (Gram-negative) was identified and analyzed. It exhibited exceptional survival at 9% (w/v) NaCl salinity. Whole-genome sequencing revealed a circular chromosome spanning 3,875,470 bp with 63.11% GC content, encoding 5534 protein-coding genes. AntiSMASH analysis predicted eight secondary metabolite biosynthetic gene clusters. Genomic annotation identified functional genes associated with nitrogen cycle coordination, phytohormone biosynthesis, micronutrient management and osmoprotection. Integrating genomic evidence with the existing literature suggests RH-AZ's potential for enhancing rice salt tolerance and promoting the growth of rice plants. Subsequent physiological investigations revealed that the RH-AZ strain had significant growth-promoting effects on rice under high salinity stress. Compared with a non-inoculated control, RH-AZ-inoculated rice plants exhibited stem elongation and fresh biomass enhancement under salt stress conditions. The RH-AZ strain concurrently affected key stress mitigation biomarkers: it enhanced the activity of antioxidant enzymes including superoxide dismutase, peroxidase, catalase and ascorbate peroxidase, and the contents of proline and chlorophyll in plants, and reduced the content of malondialdehyde. These findings demonstrate that R. marinum RH-AZ, as a multifunctional bioinoculant, enhances rice salt tolerance by enhancing the stress responses of the plants, presenting a promising solution for sustainable agriculture in saline-affected ecosystems.