Water Disinfection Byproducts Increase Natural Transformation Rates of Environmental DNA in Acinetobacter baylyi ADP1

The process of natural transformation allows for the stable uptake, integration, and functional expression of extracellular DNA. This mechanism of horizontal gene transfer has been widely linked to the acquisition of antibiotic resistance and virulence factors. Here, we demonstrate that bromoacetic acid (BAA)a regulated drinking water disinfection byproduct (DBP)can stimulate natural transformation rates in the model organism Acinetobacter baylyi ADP1. We demonstrate that transformation stimulation in response to BAA is concentration-dependent and is linked to the ability of this compound to generate DNA damage via oxidative stress. In presence of BAA, transcription of recA was upregulated 20–40% compared to the nontreated controls, indicating that this component of the DNA damage response could be associated with the increase in transformation. Other genes associated with DNA translocation across the cytoplasmic membrane (i.e., pilX, comA) did not exhibit increased transcription in the presence of BAA, indicating that the enhancement of transformation is not associated with increased translocation rates of environmental DNA. Overall, these results lead us to speculate that elevated recA transcription levels could lead to increased integration rates of foreign DNA within the recipient cell during DNA repair. Lastly, we show that an artificial DBP cocktail simulating the environmental concentrations of five water DBP classes stimulates natural transformation by almost 2-fold. The results of this study suggest that mutagens like DBPs may play an important role in enhancing the fixation rates of extracellular DNA in the environmental metagenome.自然转化（natural transformation）过程可实现胞外DNA的稳定摄取、整合与功能性表达。该水平基因转移（horizontal gene transfer）机制已被广泛证实与抗生素耐药性及毒力因子的获取密切相关。本研究证实，溴乙酸（bromoacetic acid, BAA）——一种受管制的饮用水消毒副产物（disinfection byproduct, DBP）——能够提升模式生物拜氏不动杆菌（Acinetobacter baylyi）ADP1的自然转化速率。研究发现，BAA引发的转化刺激效应呈浓度依赖性，且与该化合物通过氧化应激诱导DNA损伤的能力直接相关。与未处理对照组相比，BAA处理组中recA基因的转录水平上调20%~40%，这表明DNA损伤应答通路中的该组分或与转化效率提升存在关联。其他参与细胞质膜DNA转运的基因（如pilX、comA）在BAA存在条件下未出现转录上调，提示转化效率的增强并非源于环境DNA转运速率的提升。综上，本研究结果推测：升高的recA转录水平或可在DNA修复过程中提升受体细胞对外源DNA的整合速率。最后，本研究证实，模拟五类饮用水消毒副产物环境浓度的人工消毒副产物混合物，可使自然转化效率提升近2倍。本研究结果提示，诸如消毒副产物这类诱变剂或许在提升环境宏基因组中外源DNA的固定速率方面发挥着重要作用。