Simultaneous Trichloroacetate Dechlorination Metabolism and Nitrogen Fixation in Nitrogen-Limited Aquifers

Haloacetates, particularly trichloroacetate (TCAA), are
pervasive
contaminants, yet their biotransformation in anoxic, nutrient-limited
environments remains poorly understood. Here, we elucidate a geographically
widespread attenuation of haloacetates in nutrient-limited aquifers
by field surveys across six Chinese provinces. Enrichment cultures
metabolized TCAA as the sole carbon and energy source. Major metabolites
(oxalate, acetate, CO2) indicated complete hydrolytic dechlorination
accompanied by fermentation and mineralization. Isotope labeling and
chemical probe studies confirmed the simultaneous occurrence of TCAA
dechlorination and nitrogen fixation under fixed nitrogen-limited
conditions. Integrated metagenomic, metabolomic, and transcriptional
analyses demonstrated nitrogen-regulated metabolic reconfiguration.
Acetyl-CoA potentially associated with TCAA metabolism may enter the
TCA cycle under nitrogen-limited conditions. Dehalogenase gene (had) homologues extensively co-occurred with homologues
of nitrogenase genes (nifHDK) in oligotrophic environments.
Potential cross-feeding interactions among unclassified Azospira sp., Ralstonia pickettii, and Azospira inquinata mediated
carbon–nitrogen intermediate exchange. This study identifies
a previously unrecognized process that enables simultaneous TCAA detoxification
and nitrogen acquisition in oligotrophic aquifers, thereby proposing
an energy-conserving and ecologically adaptive strategy for haloacetate
bioremediation.