Microbes in BES glyphosate degradation
Recent evidence suggests that glyphosate, the most widely herbicide globally, is accumulating in the environment and may have undesirable ecotoxicity and human toxicity. While natural attenuation of glyphosate has been reported, the efficacy varied considerably under varying environmental conditions and the dominant metabolite, aminomethylphosphonic acid (AMPA), is possibly more persistent and toxic. This study investigated the feasibility of using bioelectrochemical system (BES) to enhance the degradation of glyphosate under an anaerobic, reductive conditions. Atomistic simulations using Density Functional Theory (DFT) predicted increased thermodynamic favorability for the non-dominant decomposition pathway upon the introduction of an external charge to the system, suggesting decreased AMPA production compared to a system without an applied potential. Experimental results confirmed that cathodic poised potential (-0.4V vs. Ag/AgCl) facilitated the degradation of glyphosate (i.e., 75% removal in BES vs. ~40% removal in the control conditions) through stimulating the C-P lyase degradation pathway. On the basis of mol AMPA yield per mol glyphosate removal, the generation of AMPA was significantly lower in the BES treatment condition than in the non-BES treatment conditions and previous biodegradation studies (i.e., 0.52 mol/mol vs. typically 0.56-1.00 mol/mol in others). Geobacter lovleyi was likely the key active species in the enhanced C-P lyase pathway, as evidenced by the preservation of its electron transfer genes (such as NADH-quinone oxidoreductase submit B and subunit K, cytochrome c3, and ferredoxin) and the up-regulation of its hydroxylamine reductase genes in the metagenomic analysis.