2,4-Dichlorophenoxyacetic acid (2,4-D) is the third most applied pesticide in Brazil to control broadleaf weeds in crop cultivation and pastures. Due to 2,4-D’s high mobility and long half-life under anoxic conditions, this herbicide has high probability for groundwater contamination. Bioremediation is an attractive solution for 2,4-D contaminated anoxic environments, but there is limited understanding of anaerobic 2,4-D biodegradation. In this study, methanogenic enrichment cultures were obtained from Amazonian top soil (0—40 cm) and deep soil (50 -80 cm below ground) that biotransform 2,4-D (5 µM) to 4-chlorophenol and phenol. When these cultures were transferred (10% v/v) to fresh medium containing 40 µM or 160 µM 2,4-D, the rate of 2,4-D degradation decreased, and biotransformation did not proceed beyond 4-chlorophenol and 2,4-dichlorophenol in the top and deep soil cultures, respectively. 16S rRNA gene sequencing and qPCR of a selection of microbes revealed no significant enrichment of known organohalide-respiring bacteria. Furthermore, a member of the genus Cryptanaerobacter was identified as possibly responsible for phenol conversion to benzoate in the top soil inoculated culture. Overall, these results demonstrate the effect of 2,4-D concentration on biodegradation and microbial community composition, which are both important factors when developing pesticide bioremediation technologies.

2,4-二氯苯氧基乙酸 (2,4-D) 是巴西第三大用于控制农作物种植和牧场阔叶杂草的农药。由于2,4-D的高迁移率和缺氧条件下的半衰期长，该除草剂污染地下水的可能性很高。生物修复对于 2,4-D 污染的缺氧环境来说是一种有吸引力的解决方案，但对厌氧 2,4-D 生物降解的了解有限。在本研究中，从亚马逊表层土壤（0-40 cm）和深层土壤（地下 50 -80 cm）获得产甲烷富集培养物，将 2,4-D (5 µM) 生物转化为 4-氯酚和苯酚。当这些培养物转移（10% v/v）至含有 40 µM 或 160 µM 2,4-D 的新鲜培养基时，2,4-D 降解率降低，并且生物转化不会进行超过 4-氯苯酚和 2, 4-二氯苯酚分别存在于表层和深层土壤培养物中。对选定微生物的 16S rRNA 基因测序和 qPCR 显示，已知的有机卤化物呼吸细菌没有显着富集。此外，隐菌属的一个成员被鉴定为可能在表层土壤接种培养物中将苯酚转化为苯甲酸盐的原因。总的来说，这些结果证明了 2,4-D 浓度对生物降解和微生物群落组成的影响，这都是开发农药生物修复技术时的重要因素。