Exploring the Interactive Mechanisms of Halophilic Bacterium SPSB2 and Mannitol in Mitigating Sodium Chloride and Arsenic Stress in Tomato Plants

Agricultural productivity is adversely affected by soil salinization and contamination with heavy metals, emphasizing the necessity for environmentally friendly technologies. This study investigates the impact of sodium chloride (NaCl) and arsenic (As) stress on tomato seedlings and explores the stress-alleviating effects of mannitol and a halophilic bacterium, Nitratrieducator aquimarinus SPSB2. Our results revealed that bacteria strainSPSB2 establishes a symbiotic relationship with tomato plants, which modulates the secondary metabolites and antioxidant system in tomato plants exposed to both NaCl and As stress. Under the NaCl and As stress tomato seedling growth was significantly reduced, although this reduction was mitigated by bacteria strain SPSB2 and mannitol treatment. When exposed to NaCl stress, the bacterial strain enhances shoot and root length by 84.8% and 152.5%, respectively. Similarly, under the As stress conditions, bacteria strain SPSB2 inoculation increased the shoot and root weights by 63.1% and 45.5%, respectively. Bacteria strain SPSB2 inoculation also significantly enhanced the chlorophyll a, b, and carotenoid contents by 76.3%, 78%, and 50%, respectively, compared to their non-inoculated counterparts under As stress conditions. Furthermore, during NaCl and As stress conditions, treatments with SPSB2 and mannitol increase the levels of enzymatic components (catalase, polyphenol oxidases) and non-enzymatic components (flavonol protein, sugar, starch), indicating a stress-alleviating effect of bacteria strain SPSB2 and mannitol. In the current study, the bacteria strain SPSB2 was more effective than mannitol in improving tomato plants' salinity and heavy metal tolerance regarding growth and physiological attributes. The symbiotic relationship between SPSB2 and tomato plants positively impacted various parameters, including plant growth, chlorophyll content, and antioxidant system activity. Moreover, the study suggests that SPSB2 is more effective than mannitol in improving tomato plants' salinity and heavy metal tolerance. These findings contribute to the understanding of environmentally friendly strategies for managing soil salinization and heavy metal contamination in agriculture, and the potential use of SPSB2 in microbial-assisted phytoremediation of polluted saline soils.