Short-term responses of plant growth-promoting bacterial community to the herbicides imazethapyr and flumioxazin.

Imazethapyr and flumioxazin are widely recommended herbicides for soybean fields due to their broad-spectrum effects. However, although both herbicides present low persistence, their potential impact on the community of plant growth-promoting bacteria (PGPB) is unclear. To address this gap, this study assessed the short-term effect of imazethapyr, flumioxazin, and their mixture on the PGPB community. Soil samples from soybean fields were treated with these herbicides and incubated for 60 days. We extracted soil DNA at 0, 15, 30, and 60 days and sequenced the 16S rRNA gene. In general, the herbicides presented temporary and short-term effects on PGPB. The relative abundance of Bradyrhizobium increased, while Sphingomonas decreased on the 30th day with the application of all herbicides. Both herbicides increased the potential function of nitrogen fixation at 15th days and decreased at 30th and 60th days of incubation. The proportions of generalists were similar (∼42%) comparing each herbicide and the control, while the proportion of specialists increased (varying from 24.9% to 27.6%) with the application of herbicides. Imazethapyr, flumioxazin and their mixture did not change the complexity and interactions of the PGPB network. In conclusion, this study showed that, in the short term, the application of imazethapyr, flumioxazin, and their mixture, at the recommended field rates, does not negatively affect the community of plant growth-promoting bacteria.

Tolerance and reduction of chromium by bacterial strains.

Bacteria have potential to tolerate and reduce metals. This study evaluated the potential of selected bacterial strains in tolerating and reducing chromium (Cr). Six bacterial strains (Rhizobium miluonense LCC01, LCC04, LCC05, and LCC69; Rhizobium pusense LCC43; and Agrobacterium deltaense LCC50) showed tolerance to Cr(VI) (16 and 32 µg mL-1), reduction potential of Cr(VI) (from 50 to 80%), and efficiency in producing exopolysaccharides. Rhizobium pusense LCC43 exhibited the highest tolerance (128 µg mL-1), reduction potential of Cr(VI) (from 80 to 100%), and efficiency in producing exopolysaccharides. These results suggested that this strain may have the potential to be used in the bioremediation of soils contaminated with Cr(VI).