NOVEL BACILLUS SPP. AS PROMISING HALOTOLERANT GROWTH PROMOTING RHIZOBACTERIA FROM MANGROVE PLANT SONNERATIA CASEOLARIS

The use of salt-tolerant plant growth promoting rhizobacteria (ST-PGPR) for reducing environmental stress and enhancing quality of crops has recently emerged as a perspective for sustainable development of agriculture, especially in the context of climate change. Within the mining of potential bacterial candidates serving for such purposes, bacterial strains from rhizosphere of mangrove plants in Vietnam were isolated and characterized. Results revealed two microbial isolates from Sonneratia caseolaris, symbolized as S13 and S15, exhibited 1-aminocyclopropane-l-carboxylic acid (ACC) deaminase activity and salt tolerance up to 7% sodium chloride. These bacteria performed phosphate solubilizing property with 57.04-61.16% of degradation after 9 days in NBRIP medium. Besides, S13 and S15 showed antimicrobial activity against plant pathogens, including F. oxysporum and A. niger. By analyzing the ribosomal 16S sequences, bacterial strains S13 and S15 were identified to be Bacillus spp. with phylogenetically close relation to B. velezensis and B. siamensis, respectively. Additionally, sprouts encoated with S13 and S15 bacterial suspensions (similar to 4*10(8) CFU/L each) exhibited enhanced shoot and root elongation in both normal and saline conditions. The bacterial strains were in vitro evaluated to be nontoxic to tested cells and animals. Achieved results brought out mangrove derived ST-PGPR strains with highly applicable potential for development of saline agriculture.