Morphological, metabolomic and genomic evidences on drought stress protective functioning of endophyte Bacillus safensis Ni7, offering its application as probiotic to plant drought

Abstract

The metabolomic and genomic characterization of an endophytic Bacillus safensis Ni7 was carried out in this study. This strain has previously been isolated from the xerophytic plant Nerium indicum L. and reported to enhance the drought tolerance in C. annuum L. seedlings. The effects of drought stress on the morphology, biofilm production and metabolite production of B. safensis Ni7 were analysed by various techniques. Compared to the non-stressed conditions, the organism was found to have multiple strategies such as aggregation and clumping, robust biofilm production and increased production of surfactin homologues under the drought induced condition. The whole genome sequencing (WGS) based analysis has demonstrated B. safensis Ni7 to have a genome size of 3,671,999 bp, N50 value of 3,527,239 and a mean G + C content of 41.58%. By detailed bioinformatics analysis, Bacillus safensis Ni7 could be predicted to have the presence of genes responsible for stress response, surfactin production, biofilm production, chemotaxis, flagella synthesis etc. Besides these, genes responsible for the plant growth promotion (PGP), including those for nitrogen and sulphur assimilation and phosphate solubilisation were also predicted. The organism was also observed to have the genes for catalase, superoxide dismutase, protein homeostasis, cellular fitness, osmoprotectants production and protein folding. Further pan-genome analysis with plant associated B. safensis strains available in the public databases revealed it to have the presence of a total of 5391 gene clusters. Among these, 3207 genes were identified as core genes, 954 as shell genes and 1230 as cloud genes. This observation highlighted the variation in gene content among different strains of B. safensis which might have evolved as part of its adaptive support offered to host plants. This variation hence could possibly be attributed to the genomic basis of B. safensis for plant growth. The results of this study hence, demonstrate genomic evidences for the drought protective effect of the endophytic B. safensis Ni7 with adaptations to support plant growth which thereby confirms its promises to be applied as drought protective plant probiotic.