In-depth genome analysis of Bacillus sp. BH32, a salt stress-tolerant endophyte obtained from a halophyte in a semiarid region.

Abstract

Endophytic strains belonging to the Bacillus cereus group were isolated from the halophytes Atriplex halimus L. (Amaranthaceae) and Tamarix aphylla L. (Tamaricaceae) from costal and continental regions in Algeria. Based on their salt tolerance (up to 5%), the strains were tested for their ability to alleviate salt stress in tomato and wheat. Bacillus sp. strain BH32 showed the highest potential to reduce salinity stress (up to + 50% and + 58% of dry weight improvement, in tomato and wheat, respectively, compared to the control). To determine putative mechanisms involved in salt tolerance and plant growth promotion, the whole genome of Bacillus sp. BH32 was sequenced, annotated, and used for comparative genomics against the genomes of closely related strains. The pangenome of Bacillus sp. BH32 and its closest relative was further analyzed. The phylogenomic analyses confirmed its taxonomic position, a member of the Bacillus cereus group, with intergenomic distances (GBDP analysis) pinpointing to a new taxon (digital DNA-DNA hybridization, dDDH < 70%). Genome mining unveiled several genes involved in stress tolerance, production of anti-oxidants and genes involved in plant growth promotion as well as in the production of secondary metabolites. KEY POINTS : • Bacillus sp. BH32 and other bacterial endophytes were isolated from halophytes, to be tested on tomato and wheat and to limit salt stress adverse effects. • The strain with the highest potential was then studied at the genomic level to highlight numerous genes linked to plant growth promotion and stress tolerance. • Pangenome approaches suggest that the strain belongs to a new taxon within the Bacillus cereus group.