Psychrotolerant antarctic Mokoshia mucilaginosa and Mokoshia rubra enhance salt Stress tolerance in Nicotiana tabacum via photosynthetic stabilization and antioxidant regulation

Antarctic Mokoshia mucilaginosa and Mokoshia rubra are associated with improved salinity tolerance in Nicotiana tabacum through coordinated regulation of photosynthetic performance and antioxidant responses, highlighting the potential of polar bacteria as bioinoculants for sustainable agriculture in saline and cold-affected ecosystems. Soil salinity is an escalating global challenge that constrains crop productivity worldwide, with particularly severe impacts in marginal agroecosystems, including those in cold regions. Here, we provide evidence that two psychrotolerant Antarctic bacterial strains, Mokoshia mucilaginosa and Mokoshia rubra, function as plant growth-promoting bioinoculants that alleviate NaCl-induced stress in Nicotiana tabacum. Both strains exhibited key plant growth-promoting traits, including indole-3-acetic acid production, phosphate solubilization, siderophore production, and nitrogen fixation. Under salinity levels of 50-150 mM NaCl, bacterial inoculation was associated with improved plant performance, including enhanced biomass accumulation, improved photosystem II efficiency (Fv/Fm, Φ_PSII, PI_ABS), and increased pigment contents (chlorophylls and carotenoids), alongside modulation of antioxidant enzyme activities (SOD, POD, CAT, and APX). Fluorescence kinetics and spectral reflectance indices further revealed distinct multivariate patterns separating inoculated plants from uninoculated salt-stressed controls. Together, these results suggest that Antarctic Mokoshia spp. contribute to improved photosynthetic function and redox regulation under salinity stress. To our knowledge, this study provides the first report linking members of the genus Mokoshia with enhanced salt stress tolerance in plants, highlighting their potential as sustainable microbial tools for improving crop performance in saline agroecosystems.