Enhancement of Wheat Growth by UV-Mutagenesis of Potential Chromium Tolerant Bacillus sp. Strain SR-2-1/1

UV mutagenesis has long been known to improve bacterial strains in their physiological capacity. In the current study, we used the UV mutagenesis approach to increase the PGPR characteristics of a pre-characterized metal-tolerant PGPR strain Bacillus sp. strain SR-2-1/1 (KY315919), with the objective of increasing the physiological outcome of its PGPR traits in vitro and post inoculation on wheat plants. After UV irradiation, the results implied a substantial in vitro increase in the phosphate solubilization and ammonia production of two selected mutant strains (M₁ and M₂) as compared to the wild-type strain SR-2-1/1; however, the ACC deaminase enzyme activity was completely lost in the mutant strains, which were originally present in the wild-type strains. However, the UV mutagenesis did not affect the taxonomy of these mutant strains. Moreover, the mutant strains M₁ and M₂ survived in the rhizosphere of wheat plants up to 30 days at an optimum (approximately 7–7.5 Log CFU/mL of rhizosphere soil) population density. The fresh and dry biomass, as well as root and shoot length, of wheat plants inoculated with one of the mutant strains M₂ were significantly higher than in the wheat plants inoculated with wild-type strain SR-2-1/1. The overall results imply that the resulted mutant M₂ was a physiologically competent PGPR strain, which could be tested in field experiments as an inoculum.