Characterization of a Pure Culture of <i>Dehalogenimonas</i> Dechlorinating 4-Hydroxy-chlorothalonil and Its Putative Reductive Dehalogenase Gene by a Multiomics Approach

4-Hydroxy-chlorothalonil (4-OH-TPN), the main metabolite of the widely used fungicide chlorothalonil, has recently been reported to be reductively dechlorinated by an anaerobic consortium containing <i>Dehalogenimonas</i>. While the pure culture of the <i>Dehalogenimonas</i> has not been isolated and the reductive dehalogenase genes (<i>rdhAs</i>) responsible for the 4-OH-TPN dechlorination remain unclear. The assembled genome of <i>Dehalogenimonas</i> contained a 1,2-dichloroethane (1,2-DCA) reductive dehalogenase gene (<i>dcpA</i>) ortholog. In this study, by alternating the substrate from 4-OH-TPN to 1,2-DCA, a pure culture of <i>Dehalogenimonas</i>, designated as 4OHTPN1, was finally isolated. Strain 4OHTPN1 potentially represents a novel species in the genus <i>Dehalogenimonas</i> and contains 33 <i>rdhA</i> genes and 4 <i>rdhB</i> genes. The novel <i>rdhA26</i> gene (designated <i>htpnA</i>) was identified as the key gene involved in 4-OH-TPN dechlorination. Its transcriptional and protein expression levels were 25.0-fold and 10.2-fold higher than the average of all <i>rdhA</i> genes when the culture was solely amended with 4-OH-TPN. In contrast, the <i>dcpA</i> ortholog, <i>rdhA25</i>, exhibited 10.1-fold and 9.8-fold higher transcriptional and protein expression levels when only amended with 1,2-DCA, highlighting a substrate-specific regulatory response to a distinct electron acceptor. This study expands our knowledge of the <i>rdhA</i> gene for 4-OH-TPN dechlorination in the pure culture of <i>Dehalogenimonas</i>.