Characterization of Marinobacter sp. ZP-590, a Rhizobacterium That Promotes Maize Growth Under Saline Conditions

Soil salinization is a challenge for global agriculture and can affect the yield of staple crops such as maize. Plant growth-promoting rhizobacteria (PGPR) are known to play a pivotal role in enhancing plant growth and stress resilience. However, no studies so far have reported plant growth-promoting (PGP) activity in members of the genus Marinobacter. In this study, a novel strain of Marinobacter sp. ZP-590, was identified as a PGPR based on a polyphasic taxonomic analysis, which was isolated from the rhizosphere soil of Tamarix chinensis Lour. Genomic analysis revealed that ZP-590 possesses 5370 protein-coding genes, including core metabolic, catalytic, and transport functions essential for bacterial survival and plant interactions, along with multiple genes potentially associated with PGP traits such as phosphate solubilization, nitrogen fixation, and the production of siderophore and exopolysaccharide (EPS), tryptophan (a prerequisite for IAA synthesis), and amylase. These genomic predictions were functionally validated through in vitro assays confirming all predicted PGP activities. Pot experiment results suggested that inoculation with ZP-590 enhanced maize growth under saline conditions. Compared to the non-inoculated controls, the treatment significantly increased root fresh weight (14.25%; p < 0.05) and stem fresh weight (125.04%; p < 0.01), while shoot height and leaf fresh weight showed no significant changes. Metabolomic profiling revealed that ZP-590 inoculation was associated with systemic metabolic changes in maize under saline conditions. A total of 394, 262, and 601 differentially accumulated metabolites in the root, stem, and leaf, respectively. These changes were characterized by a substantial up-regulation of antioxidant compounds, notably flavonoids, and changes in carbohydrate and lipid metabolism pathways. The changes in carbohydrate and lipid metabolism pathways may contribute to the supply of energy and structural components for stress adaptation. Meanwhile, the accumulation of antioxidant compounds significantly mitigated saline-induced oxidative damage by reducing the levels of superoxide anion (O2−) in leaves. In this study, Marinobacter sp. ZP-590 is characterized as a PGPR that promotes maize growth under saline conditions. These findings provide a foundation for investigating the molecular mechanisms underlying the interaction between ZP-590 and maize under saline conditions.