Plant Beneficial Deep-Sea Actinobacterium, MT1.1 Promote Growth of Tomato () under Salinity Stress.

Salt stress is a serious agricultural problem threatens plant growth and development resulted in productivity loss and global food security concerns. Salt tolerant plant growth promoting actinobacteria, especially deep-sea actinobacteria are an alternative strategy to mitigate deleterious effects of salt stress. In this study, we aimed to investigate the potential of deep-sea MT1.1 to mitigate salt stress in tomato seedlings and identified genes related to plant growth promotion and salt stress mitigation. MT1.1 exhibited plant growth promoting traits namely indole-3-acetic acid (IAA) and siderophore production and phosphate solubilization under 0, 150, 300, and 450 mM NaCl in vitro. Inoculation of MT1.1 improved tomato seedlings growth in terms of shoot length and dry weight compared with non-inoculated seedlings under 150 mM NaCl. In addition, increased total soluble sugar and total chlorophyll content and decreased hydrogen peroxide content were observed in tomato inoculated with MT1.1. These results suggested that this strain mitigated salt stress in tomatoes via osmoregulation by accumulation of soluble sugars and HO scavenging activity. Genome analysis data supported plant growth promoting and salt stress mitigation potential of MT1.1. Survival and colonization of MT1.1 were observed in roots of inoculated tomato seedlings. Biosafety testing on MT1.1 and in silico analysis of its whole genome sequence revealed no evidence of its pathogenicity. Our results demonstrate the potential of deep-sea MT1.1 to mitigate salt stress in tomato seedlings and as a candidate of eco-friendly bio-inoculants for sustainable agriculture.