Microbial Cooperative Molecular Strategies Enabling 1,2-Dichloroethane Detoxification in Low pH Aquifers

Organohalide-respiring bacteria (OHRB) play a critical role in the bioremediation of halogenated pollutants. However, their activity is often compromised in naturally occurring acidic environments that impose substantial physiological stress with only a few OHRB remaining functional. The mechanisms enabling these acid-tolerant OHRB to thrive under low-pH environments remain largely unexplored. Desulfitobacterium sp. strain AusDCA is one such acid-tolerant OHRB, capable of respiring 1,2-dichloroethane to ethene across a broad pH range, with dechlorination activity still observed at pH 5.0, though at a rate 86.9% lower than that at pH 7.0. Proteomic analysis revealed a shift in electron transfer strategy under acid stress at pH 5.5, with downregulation of hydrogenases and upregulation of NADH-quinone oxidoreductase, suggesting reliance on NADH as the primary electron donor. Other acid tolerant mechanisms for mitigation of intracellular protons included the upregulation of decarboxylases, nitrogen cycling genes, and basic amino acid production as well as reduced ethanolamine consumption. Energy conservation adaptation involved upregulation of nicotinate fermentation and downregulation of 3-hydroxybutyrate production and flagellation. These adaptations enabled strain AusDCA to maintain respiratory activities and support reductive dehalogenation under acidic conditions, offering insights into microbial adaptation and potential strategies for low-pH bioremediation.