Effects of different carbon substrates on performance, microbiome community structure and function for bioelectrochemical-stimulated dechlorination of tetrachloroethylene

Bioelectrochemical stimulation is regarded as a promising approach for enhanced dechlorination of chlorinated aliphatic hydrocarbons (CAHs). However, variation in microbiome structure and function corresponding to different carbon substrates remain poorly understood. In this study, tetrachloroethylene (PCE)-dechlorinating biocathode systems were established acclimating with glucose, sodium acetate (NaAc), or NaHCO3 as the carbon substrates. The dechlorination rates achieved in the constructed biocathode were 4.1-26.5 times higher than those in sole electrochemical or microbial systems, verifying the outstanding dechlorination capacity by bioelectrochemical stimulation. Carbon substrate types markedly affected cathodic biofilm microbiome structure and function. Different PCE dechlorination rates were observed with first-order kinetic constants (k) of 0.110 +/- 0.002, 0.056 +/- 0.002, and 0.032 +/- 0.001 h(-1) for glucose, NaAc, and NaHCO3, respectively. Cis-1,2-dichloroethene and ethene were the major and minor dechlorination products for all systems. Microbiome structure and network analysis revealed that all three kinds of carbon substrate-fed systems enriched large proportions of dechlorinators and cathode-respiring bacteria but were significantly distinct in composition, such as Lactococcus and Anaeroarcus by glucose, Geobacter and Pseudomonas by NaAc, and Bacillus by NaHCO3. However, several cathode-respiring dechlorinators shared the center of network, such as Desulfovibrio and Pseudomonas. Difference in microbiome function was further supported by the abundance of putative functional genes, and heterotrophic (glucose/NaAc) systems were more conducive to enrich reductive dehalogenase (pceA and tceA) and electroactive omcX genes than the autotrophic (NaHCO3) system. This study provides insights into microbiome working mechanism for bioelectrochemical dechlorination of CAHs under different carbon substrate surroundings.