Chlorinated ethenes (CEs) are common groundwater pollutants widely used in dry cleaning and degreasing. CEs remain prominent pollutants at active Superfund sites. Bioremediation of CEs by Dehalococcoides sp. (Dhc) is a promising technology for site clean-up. However, due to the lack of substrate, competition for electron donor and growth co-factors (e.g., Vitamin B12) with indigenous microbes, active Dhc populations could decline significantly after bioaugmentation and fail to achieve clean-up goals. To mimic the problem, a commercially available CE-dechlorinating consortium SDC-9, with Dhc as the dominant CE dechlorinator, was starved and refrigerated for two years. This SDC-9 culture lost its capability to transform tetrachloroethene (PCE) to ethene and stopped at cis-dichloroethene (cDCE). The malfunctioning SDC-9 culture was mixed with biochar synthesized at different pyrolysis temperatures (i.e., 350, 500, 700 and 900 °C) and fed PCE and lactate. Live controls without any biochar and surface controls amended with sands were also constructed and fed PCE and lactate. The concentration of CEs, ethene and methane were monitored over time, and after 82 days of inoculation, DNA and RNA were extracted from both suspended phase in the liquid or attached phase in the biochar. In live controls, ethene production did not occur, and PCE transformation stopped at cDCE. In contrast, PCE transformation to ethene occurred in all biochar-amended bottles. Nucleic acids were shotgun-sequenced and subsequent analyses for differential gene expression and functional redundancy were performed. Examining gene expression between treatments and controls and between the attached cells in the biochar and the suspended cells in the liquid yielded insights into Dhc recovery and ethene production after biochar addition. For example, microorganisms belonging to genus Bact-08 (family Bacteroidales), species Dehalococcoides mccartyi and Cloacibacillus evryensis showed the most significant increase in gene expression compared to the controls, while microorganisms belonging to species Aminobacterium sp002432275 and Clostridium tyrobutyricum showed the most significant decreased gene expression levels. Determining the function of differentially expressed genes are ongoing. Overall, biochar contributed to recovery of ethene production by Dhc. We expect that further gene expression analyses will shed the light on how Dhc recovered and interacted with other microorganisms and materials.

Han Cao

Appearances