Trichloroacetate Dechlorination Metabolism Widely Couples to Nitrogen Fixation in Nitrogen-Limited Aquifers
Nitrogen (N) limitation significantly constrains the microbial transformation of organohalides in oligotrophic and mining-impacted aquifers. In this study, we elucidate a geographically widespread biogeochemical coupling between hydrolytic dechlorination of chloroacetic acids and nitrogen fixation in nitrogen-deficient environments. Trichloroacetate (TCAA) is anaerobically dechlorinated to oxalate and further metabolized via the tricarboxylic acid cycle to generate energy, compensating for the energy-intensive nitrogen fixation. Conversely, oxalate undergos fermentation to volatile fatty acids according to mass flux balance. Integrated metagenomic and transcriptional analyses identifies a-haloacid dehalogenases (HADs) in Ralstonia pickettii and Azospira sp. mediating TCAA transformation. A novel identified HAD1 in Azospira sp. forms a distinct phylogenetic clade and HADs frequently co-ocuurs with nitrogenase gene cluster. This metabolic integration enables simultaneous dehalogenation and nitrogen regeneration, highlighting microbial ecological plasticity in nutrient-limited aquifers. These findings provide mechanistic insights into organohalides attenuation and inform sustainable bioremediation strategies in carbon- and nitrogen-constrained environments.
Nitrogen (N) limitation significantly constrains the microbial transformation of organohalides in oligotrophic and mining-impacted aquifers. In this study, we elucidate a geographically widespread biogeochemical coupling between hydrolytic dechlorination of chloroacetic acids and nitrogen fixation in nitrogen-deficient environments. Trichloroacetate (TCAA) is anaerobically dechlorinated to oxalate and further metabolized via the tricarboxylic acid cycle to generate energy, compensating for the energy-intensive nitrogen fixation. Conversely, oxalate undergos fermentation to volatile fatty acids according to mass flux balance. Integrated metagenomic and transcriptional analyses identifies a-haloacid dehalogenases (HADs) in Ralstonia pickettii and Azospira sp. mediating TCAA transformation. A novel identified HAD1 in Azospira sp. forms a distinct phylogenetic clade and HADs frequently co-ocuurs with nitrogenase gene cluster. This metabolic integration enables simultaneous dehalogenation and nitrogen regeneration, highlighting microbial ecological plasticity in nutrient-limited aquifers. These findings provide mechanistic insights into organohalides attenuation and inform sustainable bioremediation strategies in carbon- and nitrogen-constrained environments.