Biochar alleviated the toxicity of atrazine to soybeans, as revealed by soil microbial community and the assembly process.

Atrazine has a detrimental effect on soybean growth in corn-soybean rotation systems. A knowledge gap exists regarding how rhizosphere microbial interactions respond to atrazine stress, and specifically, whether they may alleviate the detriment of atrazine on soybeans, this serving as a target to alleviate the adverse impact. Biochar are widely used for remediation in herbicide contamination soil, however, little is known about how biochar fuels the microbiomes in rhizosphere to improve soybean performance. We investigated the response of the microbial community to atrazine stress with and without biochar application to soybean cultivation in a greenhouse experiment. Atrazine had detrimental effects on soybeans and nodules, reshaping the microbial community in both the bulk and rhizosphere soil. Biochar application was able to ameliorate atrazine effects on soybean and nodule activity, with an increase in competition among microbes in the soybean rhizosphere soils. Biochar favored the probiotics such as the bacteria Lysobacter, Paenarthrobacter, and Sediminibacterium in the rhizosphere soils. The relative abundance of Lysobacter exhibited strong-negative correlations with potential pathogens. Elastic net regression with bioindicators and environmental factors accurately predicted the residual content of atrazine in soil. Collectively, our results provide a practical strategy of using biochar to improve soil quality for corn-soybean rotation that is contaminated with residual atrazine. Overall, beneficial plant microbes and changes in microbial interactions and assembly processes in the soybean rhizosphere are capable of alleviating atrazine stress on soybean growth.

Selection of a variant of Geobacter sulfurreducens with enhanced capacity for current production in microbial fuel cells.

Geobacter sulfurreducens produces current densities in microbial fuel cells that are among the highest known for pure cultures. The possibility of adapting this organism to produce even higher current densities was evaluated. A system in which a graphite anode was poised at -400 mV (versus Ag/AgCl) was inoculated with the wild-type strain of G. sulfurreducens, strain DL-1. An isolate, designated strain KN400, was recovered from the biofilm after 5 months of growth on the electrode. KN400 was much more effective in current production than strain DL-1. This was apparent with anodes poised at -400 mV, as well as in systems run in true fuel cell mode. KN400 had current (7.6A/m(2)) and power (3.9 W/m(2)) densities that respectively were substantially higher than those of DL1 (1.4A/m(2) and 0.5 W/m(2)). On a per cell basis KN400 was more effective in current production than DL1, requiring thinner biofilms to make equivalent current. The enhanced capacity for current production in KN400 was associated with a greater abundance of electrically conductive microbial nanowires than DL1 and lower internal resistance (0.015 versus 0.130 Omega/m(2)) and mass transfer limitation in KN400 fuel cells. KN400 produced flagella, whereas DL1 does not. Surprisingly, KN400 had much less outer-surface c-type cytochromes than DL1. KN400 also had a greater propensity to form biofilms on glass or graphite than DL1, even when growing with the soluble electron acceptor, fumarate. These results demonstrate that it is possible to enhance the ability of microorganisms to electrochemically interact with electrodes with the appropriate selective pressure and that improved current production is associated with clear differences in the properties of the outer surface of the cell that may provide insights into the mechanisms for microbe-electrode interactions.