In total, 140 halotolerant bacterial strains were isolated from both the soil of barren fields and the rhizosphere of six naturally growing halophytic plants in the vicinity of the Yellow Sea, near the city of Incheon in the Republic of Korea. All of these strains were characterized for multiple plant growth promoting traits, such as the production of indole acetic acid (IAA), nitrogen fixation, phosphorus (P) and zinc (Zn) solubilization, thiosulfate (S2O3) oxidation, the production of ammonia (NH3), and the production of extracellular hydrolytic enzymes such as protease, chitinase, pectinase, cellulase, and lipase under in vitro conditions. From the original 140 strains tested, on the basis of the latter tests for plant growth promotional activity, 36 were selected for further examination. These 36 halotolerant bacterial strains were then tested for 1- aminocyclopropane-1-carboxylic acid (ACC) deaminase activity. Twenty-five of these were found to be positive, and to be exhibiting significantly varying levels of activity. 16S rRNA gene sequencing analyses of the 36 halotolerant strains showed that they belong to 10 different bacterial genera: Bacillus, Brevibacterium, Planococcus, Zhihengliuella, Halomonas, Exiguobacterium, Oceanimonas, Corynebacterium, Arthrobacter, and Micrococcus. Inoculation of the 14 halotolerant bacterial strains to ameliorate salt stress (150 mM NaCl) in canola plants produced an increase in root length of between 5.2% and 47.8%, and dry weight of between 16.2% and 43%, in comparison with the uninoculated positive controls. In particular, three of the bacteria, Brevibacterium epidermidis RS15, Micrococcus yunnanensis RS222, and Bacillus aryabhattai RS341, all showed more than 40% increase in root elongation and dry weight when compared with uninoculated saltstressed canola seedlings. These results indicate that certain halotolerant bacteria, isolated from coastal soils, have a real potential to enhance plant growth under saline stress, through the reduction of ethylene production via ACC deaminase activity.

Soil salinity, being a part of natural ecosystems, is an increasing problem in agricultural soils throughout the world. Pseudomonas frederiksbergensis OS261 has already been proved to be an effective bio-inoculant for enhancing cold stress tolerance in plants however its effect on salt stress tolerance is unknown. The main aim of the present study was to elucidate Pseudomonas frederiksbergensis OS261 mediated salt stress tolerance in red pepper. The plants were exposed to a salt stress using NaCl at the concentrations of 50 mM, 100 mM and 150 mM after twelve days of transplantation, while plant growth and enzyme activity were estimated fifty days after sowing. The height in P. frederiksbergensis OS261 inoculated plants was significantly increased by 19.05%, 34.35%, 57.25%, and 61.07% compared to un-inoculated controls at 0 mM, 50 mM, 100 mM and 150 mM of NaCl concentrations respectively under greenhouse conditions. The dry biomass of the plants increased by 31.97%, 37.47%, 62.67%, and 67.84% under 0 mM, 50 mM, 100 mM and 150 mM of NaCl concentrations respectively. A high emission of ethylene was observed in un-inoculated red pepper plants under salinity stress. P. frederiksbergensis OS261 inoculation significantly reduced ethylene emission by 20.03%, 18.01%, and 20.07% at 50 mM, 100 mM and 150 mM of NaCl concentrations respectively. Furthermore, the activity of antioxidant enzymes (ascorbate peroxidase, superoxide dismutase, and catalase) also varied in the inoculated red pepper plants. Salt stress resistance in the bacterized plants was evident from the improved antioxidant activity in leaf tissues and the decreased hydrogen ion concentration. Thus, we conclude that P. frederiksbergensis OS261 possesses stress mitigating property which can enhance plant growth under high soil salinity by reducing the emission of ethylene and regulating antioxidant enzymes.