Reductive Dechlorination of 2,3-Dichloroaniline by Dehalobacter 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 Dehalobacter. 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 Dehalobacter 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, μmax, was 0.18 ± 0.03 day–1 with a half-saturation constant, Ks,
at 45 ± 16 mg/L. The first-order decay constant for Dehalobacter 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.