Abstract
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 (M-1 and M-2) 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 M-1 and M-2 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 M-2 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 M-2 was a physiologically competent PGPR strain, which could be tested in field experiments as an inoculum.