Soil microbial communities and degradation of pesticides in greenhouse effluent through a woodchip bioreactor. Soil metagenome

Pesticides, including insecticides and fungicides, are major contaminants in the effluent from intensive agricultural systems, such as greenhouses. Because of their constant use and persistence, some pesticides can accumulate in soil and/or run off into adjacent waterways. Microbial communities in soil can degrade some pesticides, and bioreactors with enhanced microbial communities have the potential to facilitate decontamination before the effluent is released into the environment. In this study, we sampled the soil along a gradient from immediately below greenhouses, into, through and below a bioreactor. Multi-analyte pesticide screening was undertaken along with shotgun metagenomic sequencing, to assess microbial community taxonomic profiles and metabolic pathway responses for functional analysis. Two insecticides (imidacloprid and fipronil) and nine fungicides were identified in the soil samples, with a general decrease in most pesticides with distance from the greenhouses. Diversity indexes of taxonomic profiles show changes in the microbial community along the gradient. In particular, microbial communities were significantly different in the bioreactor, with lower Shannon diversity compared to immediately below the greenhouses, in the channels leading into the bioreactor and further downstream. Metabolic pathway analysis revealed significant changes in a wide range of core housekeeping genes such as protein/amino acid synthesis and lipid/fatty acid biosynthesis among the sampling sites. The result demonstrates that the composition and potential functional pathways of the microbial community shifted towards an increased tendency for contaminant degradation in the bioreactor. This highlights the potential to use enhanced microbial communities within bioreactors to reduce pesticide contamination of aquatic ecosystems by run-off from greenhouses.

农药（包括杀虫剂与杀菌剂）是温室等集约化农业系统排放废水中的主要污染物。由于其持续施用与自身持久性，部分农药可在土壤中累积，或随径流进入周边水体。土壤中的微生物群落可降解部分农药，而搭载强化微生物群落的生物反应器（bioreactors）具备在废水排放至环境前实现净化的潜力。本研究沿梯度采集土壤样品，采样点涵盖温室正下方、生物反应器进水段、生物反应器内部及生物反应器下游区域。研究采用多组分农药筛查法结合鸟枪法宏基因组测序（shotgun metagenomic sequencing），以评估微生物群落的分类学特征与代谢通路响应，开展功能分析。土壤样品中共检出2种杀虫剂（吡虫啉（imidacloprid）与氟虫腈（fipronil））及9种杀菌剂，多数农药的含量随距温室距离的增加呈普遍下降趋势。分类学特征的多样性指数显示，微生物群落沿采样梯度发生显著变化。具体而言，生物反应器内的微生物群落与温室正下方、反应器进水渠及更下游区域的群落存在显著差异，其香农多样性指数（Shannon diversity）低于上述区域。代谢通路分析显示，各采样位点间一系列核心持家基因（housekeeping genes）的表达发生显著变化，包括蛋白质/氨基酸合成以及脂质/脂肪酸生物合成相关通路。研究结果表明，生物反应器内微生物群落的组成与潜在功能通路向污染物降解能力增强的方向偏移。该发现凸显了利用搭载强化微生物群落的生物反应器，降低温室径流导致的水生生态系统农药污染的应用潜力。