Improvement of simazine degradation by inoculation of corn and soybean plants with rhizobacteria

We isolated the strains of aerobic bacteria, that were able to use the simazine (2-chloro4,6-bis(ethylamino)-s-triazine) herbicide as a sole source of nitrogen, from the roots of corn plants and the nodules of soybean plants. Partial base sequences of 16S rRNA genes and physiological characteristics of the representative isolates revealed that they belonged to Agrobacterium radiobacter and Bradyrhizobium japonicum, respectively. Inoculation of corn plants with the isolates of A. radiobacter resulted in a faster decrease in the amount of simazine in vermiculite soil. Neither bacteria nor corn plants alone were able to promote the decrease in the amount of simazine. Soybean plants modulated by the isolates of B. japonicum were more sensitive to simazine in a hydroponic medium compared to non-nodulated soybeans, though a significant decrease in the amount of simazine in the media was observed. The results obtained in the present study indicate that the rhizosphere of corn and soybean plants containing root nodules is an appropriate habitat for simazine-degrading bacteria to degrade the herbicide.