Conductive material and AHLs addition altered soil microbiome and facilitated γ-HCH dechlorination but inhibited CH4 cumulation

Soil microbiome is the cornerstone of sustaining soil ecosystem services and performs an array of vital soil functions. Manipulating soil microbiome is a promising strategy to regulate soil ecosystem function, however, the effect and underlying mechanism for chlorinated organic pollution remediation are limited and the capacity to simultaneously control multiple redox processes is still unclear. Here, the dynamics of the biocathode microbial community after separately or synchronously adding conductive material and acyl-homoserine lactone (AHL) were investigated from the perspectives of electron transfer and microbial assembly in γ-hexachlorocyclohexane (γ-HCH) polluted soil-based bioelectrochemical system. The resulting responses of NO3−/Fe(III)/SO42− reduction, γ-HCH dechlorination, and CH4 cumulation were also analyzed. Two conductive materials of biochar (BC) and magnetite nanoparticle (NaFe) and two AHLs including N-butanoyl homoserine lactone (C4-HSL) and 3-oxo-hexanoyl-homoserine lactone (3OC6-HSL) were applied. Exogenous additives facilitated γ-HCH dechlorination but alleviated and even inhibited CH4 cumulation, with BC plus C4-HSL addition as the optimum. Adding BC/NaFe enriched Fe(III)-reducing bacteria and dechlorinators and selectively transferred more electrons to those electron sinks; C4-HSL/3OC6-HSL helped to increase biofilm aggregation; while BC plus C4-HSL stimulated the growth of dominant functional taxa and enhanced the compact microbial correlations. These findings broaden our insights and provide approaches to managing soil microbiomes to solve actual environmental emergencies. It shows an advanced strategy to inhibit greenhouse gas (CH4) emission when COP reduction is facilitated to achieve win-win soil remediation.