LI Chuqiao, WANG Tianyu, YIN Ying, CHEN Anliang, ZHANG Xinqi, CHEN Xuhua. Identification of a halophyte rhizobacterium B268 and its activity in microbial inhibition and salt tolerance[J]. Chinese Journal of Pesticide Science, 2022, 24(4): 771-781. DOI: 10.16801/j.issn.1008-7303.2022.0022
    Citation: LI Chuqiao, WANG Tianyu, YIN Ying, CHEN Anliang, ZHANG Xinqi, CHEN Xuhua. Identification of a halophyte rhizobacterium B268 and its activity in microbial inhibition and salt tolerance[J]. Chinese Journal of Pesticide Science, 2022, 24(4): 771-781. DOI: 10.16801/j.issn.1008-7303.2022.0022

    Identification of a halophyte rhizobacterium B268 and its activity in microbial inhibition and salt tolerance

    • To tap the resource of halotolerant biocontrol agents, a bacterial strain B268 was isolated from the rhizosphere of halophyte Casuarina equisetifolia L. It was identified based on the polyphasic taxonomic approach. The viable count method and dural culture method were used to assess the antimicrobial activities. Gene clusters related to the biosynthesis of antimicrobial compounds were predicted with antiSMASH. The influence of salt stress on biocontrol traits of B268 was analyzed by checking both the physiological activities and the gene expression levels of cells grown under NaCl gradient conditions. The effect of B268 on plant salt tolerance was evaluated with cucumber seedlings under hydroponic conditions. According to the results of polyphasic identification, strain B268 represents a novel phylotype of the conspecific Bacillus velezensis group. The NaCl concentration (W/V) for growth was 0-15% with the optimum at 3%. Thirteen gene clusters devoted to antimicrobial production were predicted in B268 genome. Nine phytopathogens tested were antagonized by B268, among which negative growth was detected in Ralstonia pseudosolanacearum treated with B268 for 8 hours, and the inhibition rate to Valsa mali var. mali, Alternaria alternate, Colletotrichum gloeosporioides, Alternaria solani were higher than 60%. The concentration of extracellular siderophore and indole-3-acetic acid reached the highest at 1% and 3% (W/V) NaCl, respectively and the phosphate solubilizing index remained stable on the NaCl gradient plates. The expression of indole-3-acetic acid biosynthesis gene dhaS and phytase coding gene phyC were maximally up-regulated at 1% (W/V) NaCl, and siderophore biosynthesis gene dhbC showed the highest expression at 3% (W/V) NaCl. In the hydroponic condition, cucumber seedlings inoculated with B268 were found to be insensitive to 80 mmol/L NaCl and tolerance to 120 mmol/L NaCl, which was illustrated by an increase of soluble sugar by 46.4% and a decrease of malondialdehyde by 67.2% in leaves. In conclusion, B268 is a halophilic biocontrol bacterium with a broad spectrum of antimicrobial activity and its growth-promoting activities show coupling responses to salt. It is suggested that B268 can be used in the biocontrol of plant pathogens or salt stress, as well as in the bioremediation of salinized soils.
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