Cathodic poised potential stimulated the electron-sensitive C-P lyase pathway in glyphosate biodegradation

Glyphosate, the most widely used herbicide globally, is accumulating in the environment and poses significant potential eco- and bio-toxicity risks. While natural attenuation of glyphosate has been reported, the efficacy varies considerably and the dominant metabolite, aminomethylphosphonic acid (AMPA), is potentially more persistent and toxic. This study investigated the bioelectrochemical system (BES) for glyphosate degradation under anaerobic, reductive conditions. Atomistic simulations using density functional theory (DFT) predicted increased thermodynamic favorability for the non-dominant C-P lyase degradation pathway under external charge, which suppressed AMPA production. Experimental results confirmed that cathodic poised potential (-0.4 V vs. Ag/AgCl) enhanced glyphosate degradation (75 % in BES vs. ∼40 % in the control conditions after 37 days), and lowered the AMPA yield (0.52 mol AMPA yield per mol glyphosate removed in BES vs. 0.77-0.86 mol mol^-1 in the control conditions). Geobacter lovleyi was likely the active species driving the C-P lyase pathway, as evidenced by the increase of its relative abundance, the upregulation of its extracellular electron transfer genes (most notably mtr) and the up-regulation of its phnJ and hcp genes (encoding C-P layse and hydroxylamine reductase respectively).