Cobalamin-autonomous Trichlorobacter facilitates robust In situ bioremediation of halogenated solvents.

Organohalide-respiring bacteria (OHRB) are key mediators of chlorinated solvent detoxification in anoxic groundwater, yet their practical application is often constrained by vitamin B₁₂ (cobalamin) auxotrophy and the requirement for strictly controlled anoxic and nutrient conditions. Here, we report the enrichment and characterization of a Trichlorobacter-dominated consortium (NB-12) that sustains efficient dihaloelimination of halogenated alkanes under minimal nutrient and relaxed anoxic constraints. The NB-12 enrichment completely transformed 1,2-dichloroethane (1,2-DCA) to ethene within 40 h (≥3.3 μmol h⁻¹) and also dechlorinated 1,2-dichloropropane and 1,1,2-trichloroethane, as well as debrominated 1,2-dibromoethane and 1,2-dibromopropane. Exogenous vitamin B₁₂ supplementation did not enhance dechlorination kinetics or product yields. Amplicon sequencing and metagenomic analyses identified Trichlorobacter lovleyi as the dominant population (>60% relative abundance) and revealed a complete anaerobic cobalamin biosynthesis pathway in the corresponding metagenome-assembled genome, indicating corrinoid autonomy at the community level. Notably, the NB-12 consortium retained sustained dehalogenation activity in non-sterile, unbuffered, and oxygen-leaky mesocosms prepared using only tap water, trace elements, and lactate-conditions mimicking challenging in situ environments. Field bioaugmentation using this "low-input" inoculant resulted in successful aquifer colonization and a reduction in 1,2-DCA concentrations in contaminated groundwater. Together, these results demonstrate that corrinoid-autonomous, Trichlorobacter-dominated enrichments can relax key physiological and operational constraints of OHR-based remediation, expanding the applicability of low-input, cost-effective strategies for in situ treatment of halogenated alkane-contaminated groundwater.