Enhancement of growth and salt tolerance of tomato seedlings by a natural halotolerant actinobacterium Glutamicibacter halophytocola KLBMP 5180 isolated from a coastal halophyte

Background and aims Soil salinity stress affects the health and growth of crops. The use of plant growth-promoting rhizobacteria (PGPR) to improve the salt tolerance of plants is gaining acceptance worldwide. Here, a halotolerant, plant growth-promoting actinobacterium Glutamicibacter halophytocola KLBMP 5180, recently isolated from the root of a coastal halophyte Limonium sinense, was investigated for its capacity on the growth of tomato seedlings under the condition of saline stress. Methods Tomato seedlings were inoculated with strain KLBMP 5180 and irrigated with 2% NaCl salt-stress treatment. Plant growth and physiological responses were determined after harvest. The genome of strain KLBMP 5180 was sequenced and analyzed. Results High salinity significantly reduced the growth and biomass of tomato seedlings. However, KLBMP 5180 inoculation significantly improved tomato growth in terms of seedling fresh weight and height, root length and fresh weight, and number of fibrous roots, along with increased osmolyte content (proline) and antioxidant defense enzymes and regulation of ion homeostasis under salt stress. From the genome, we identified a series of genes that may contribute to plant growth promotion, including genes for nitrogen fixation, biosynthesis of siderophores and exopolysaccharides. Additionally, several genes related to high salinity tolerance, such as Na+/H+ antiporter, K+ transporter, glycine-betaine synthesis and transport, and several heavy metal resistance and biodegradation genes were also identified in the genome of strain KLBMP 5180. Conclusion Our results demonstrate that the halotolerant strain KLBMP 5180 can be used to improve tomato seedling growth in saline soil and act as a potential agricultural biofertilizer agent in future applications.