A Dehalogenimonas Population Respires 1,2,4-Trichlorobenzene and Dichlorobenzenes

Chlorobenzenes are ubiquitous contaminants in groundwater and soil at many industrial sites. Previously, we demonstrated the natural attenuation of chlorobenzenes and benzene at a contaminated site inferred from a 5 year site investigation and parallel laboratory microcosm studies. To identify the microbes responsible for the observed dechlorination of chlorobenzenes, the microbial community was surveyed using 16S rRNA gene amplicon sequencing. Members of the Dehalobacter and Dehalococcoides are reported to respire chlorobenzenes; however, neither were abundant in our sediment microcosms. Instead, we observed a significant increase in the relative abundance of Dehalogenimonas from <1% to 16-30% during dechlorination of 1,2,4-trichlorobenzene (TCB), 1,2-dichlorobenzene (DCB), and 1,3-DCB over 19 months. Quantitative PCR (qPCR) confirmed that Dehalogenimonas gene copies increased by 2 orders of magnitude with an average yield of 3.6 +/- 2.3 g cells per mol Cl- released (N = 12). In transfer cultures derived from sediment microcosms, dechlorination of 1,4-DCB and monochlorobenzene (MCB) was carried out by Dehalobacter spp. with a growth yield of 3.0 +/- 2.1 g cells per mol Cl- released (N = 5). Here we show that a Dehalogenimonas population respire 1,2,4-TCB and 1,2-/1,3-DCB isomers. This finding emphasizes the need to monitor a broader spectrum of organohalide-respiring bacteria, including Dehalogenimonas, at sites contaminated with halogenated organic compounds.