Deep-Sea Actinobacteria Mitigate Salinity Stress in Tomato Seedlings and Their Biosafety Testing.

Soil salinity is an enormous problem affecting global agricultural productivity. Deep-sea actinobacteria are interesting due to their salt tolerance mechanisms. In the present study, we aim to determine the ability of deep-sea ( MT2.1 and MT2.2) to promote tomato seedlings under 150 mM NaCl compared with the terrestrial strain DSM20448. All strains exhibit in vitro plant growth-promoting traits of indole-3-acetic acid production, phosphate solubilization, and siderophore production. Tomato seedlings inoculated with MT2.1 showed higher growth parameters (shoot and root length, dry weight, and chlorophyll content) than non-inoculated tomato and the terrestrial strain under 150 mM NaCl. In addition, hydrogen peroxide (HO) in leaves of tomatoes inoculated with deep-sea was lower than the control seedlings. This observation suggested that deep-sea mitigated salt stress by reducing oxidative stress caused by hydrogen peroxide. MT2.1 showed no harmful effects on , , , and MC4100 in biosafety tests. This evidence suggests that MT2.1 would be safe for use in the environment. Our results highlight the potential of deep-sea as a plant growth promoter for tomatoes under salinity stress.