Reductive Dechlorination of 2,3-Dichloroaniline by <i>Dehalobacter</i> in an Anaerobic Enrichment Culture

2,3-dichloroaniline (2,3-DCA) has widespread use in chemical manufacturing and remains a persistent groundwater contaminant. To better understand the pathway and kinetics of its reductive dechlorination, we conducted a laboratory kinetic experiment using an anaerobic enrichment culture dominated by <i>Dehalobacter</i>. At an initial field-relevant concentration of 40 mg/L, complete and stoichiometric dechlorination of 2,3-DCA to aniline via 2-chloroaniline (2-CA) was achieved. The intermediates, 2-CA and 3-chloroaniline, were transiently formed in a ratio of 8:1. The growth yields of <i>Dehalobacter</i> on 2,3-DCA and 2-CA were 1.2 ± 0.1 × 10⁸ and 1.3 ± 0.1 × 10⁸ 16S rRNA gene copies/μmol chloride released, respectively. The maximum specific growth rate for 2,3-DCA, μ_max, was 0.18 ± 0.03 day^-1 with a half-saturation constant, <i>K</i>_s, at 45 ± 16 mg/L. The first-order decay constant for <i>Dehalobacter</i> when starved of chlorinated electron acceptors was estimated at 0.017 ± 0.001 day^-1. Lactate fermentation, acetogenesis from ethanol, syntrophic propionate oxidation, and hydrogenotrophic methanogenesis were observed during dechlorination. This work provides insights into the organohalide respiration of 2,3-DCA to aniline and advances the understanding of microbial interactions during anaerobic dechlorination. These results offer guidance for developing stable dechlorinating microbial ecosystems and key kinetic parameters for predictive modeling of groundwater 2,3-DCA fate and transport.