Phylogenetic and plant-growth-promoting characteristics of Bacillus isolated from the wheat rhizosphere

The rhizobacteria that promote the growth of plants can have a positive effect on the productivity of crops, especially in stress conditions. Among the plant -growth -promoting (PGP) rhizobacteria (PGPR) cluster, Bacillus spp. are among the genera with most potential due to their spore forming ability, thereby increasing the adaptation of Bacillus strains to commercial formulation and field application. Due to their intrinsic properties, the Bacilli have several mechanisms conferring beneficial effects on plants. Thirty-five strains of Bacillus isolated from the rhizosphere of wheat from three different soils in arid and semi-arid areas of Algeria were tested for properties involved in the promotion of plant growth. The PGP ability of the 35 strains was evaluated by determining their biofertilisation (phosphate solubilisation), biostimulation [indole acetic acid (IAA) production] and biocontrol [cyanhydric acid (HCN), siderophores, 2,3-butanediol production and antifungal activity] activities. Of the 35 strains, 78 % had the ability to solubilise phosphates at rates of 16.65 mu g/mL for strain D13, 15.60 mu g/mL for D7 and 15.05 mu g/mL for D6. These strains were the most successful and were isolated from arid and alkaline soils. The highest concentrations of IAA were produced by strains D4 and D7 to values ranging from 10 to 19 mu g/mL. All strains inhibited at least one fungal strain tested, and 75 % had activity against three fungi or more. More than half of Bacillus strains produced 2.3- butanediol but only a single strain produced HCN. Only three strains (B25, D11 and BA11) were efficient in the production of siderophores. Also, four strains (B21, D4, B10 and B25) possessed ACCdeaminase and were considered regulators of stress. Phylogenetic diversity of the strains was analysed by 16S rDNA sequencing. The results identified all strains as being similar to the Bacillus sp. cluster, and divided separately into five groups. The majority of strains (n = 28) were assigned to the species Bacillus thuringiensis and Bacillus subtilis. The Bacillus species isolated in this study showing PGP abilities have the potential to be used as PGPR.