Carbon sources mediate microbial pentachlorophenol dechlorination in soils

Highlights: • Carbon sources exhibited impacts on pentachlorophenol (PCP) dechlorination. • Citrate and lactate accelerated PCP dechlorination process. • Glucose showed no effect on PCP dechlorination process. • Citrate and lactate affected the topological properties of bacterial networks. • Clostridiales played a critical role in the key functional modules of networks. -- Abstract: In this study, experiments were performed using network analysis to investigate the effects of different carbon sources, including blank, citrate, glucose and lactate, on indigenous bacterial communities and on the pentachlorophenol (PCP) dechlorination in two soils. Kinetics results demonstrate that PCP dechlorination is significantly enhanced by adding citrate/lactate, but to a lesser extent by adding glucose. High-throughput sequencing results revealed that Firmicutes and Proteobacteria were the dominant groups in these four different treatments during the PCP dechlorination, whereas random forest analysis indicated that the orders Clostridiales, Haloplasmatales, Bacillales, Pseudomonadales and Gaiellales were the critical bacterial orders in modules that were significantly correlated with PCP dechlorination. Among them, the relative abundance of Clostridiales dramatically increased in both citrate and lactate treatment, further accelerating the PCP dechlorination. Addition of citrate/lactate as the carbon source increased the bacterial co-occurrence network density, average clustering coefficient and modularity. Moreover, more modules significantly correlated with PCP dechlorination in the citrate/lactate networks compared with the glucose/blank networks. Random forest modeling suggested that Clostridiales played a critical role in these functional modules. Taken together, our results provide insight into the biological mechanism of the impact of exogenous carbon sources on PCP dechlorination pathways by modifying soil bacterial networks.