Conjugation-Mediated Detoxification and Reactive Metabolite Risks in Microbial Degradation of a Cyano-Liquid Crystal Monomer

Cyano-substituted liquid crystal monomers (cyano-LCMs), widely used in electronic display manufacturing, have emerged as persistent and potentially bioaccumulative contaminants in aquatic environments. However, their microbial transformation mechanisms remain largely unknown. Herein, we report the first characterization of the aerobic microbial biotransformation pathway of 4′-(hexyloxy)-4-biphenylcarbonitrile (6OCB), a representative cyano-LCM, by Sphingopyxis sp. strain ZD-6 isolated from e-waste-contaminated soil. Under aerobic conditions, 92.4% of 6OCB was degraded within 6 days. A total of 13 metabolites were detected, including eight phase II conjugates, indicating a two-step degradation mechanism involving initial oxidative, reductive, and hydrolytic transformations leading to reactive intermediates, followed by conjugation reactions, yielding diverse phase II products, including glutathione-conjugated metabolites. Genomic and transcriptomic analyses identified key enzymes, FAD-dependent oxidoreductases, glutathione S-transferases, and glutamine synthetase, potentially involved in these transformations. Most conjugates showed reduced predicted toxicity, whereas lipid-bound derivatives tended to exhibit higher predicted toxicity. These findings highlight the role of microbial phase II metabolism in cyano-LCM transformation and emphasize the importance of evaluating the environmental fate and potential risk of conjugated metabolites in future risk assessment and bioremediation strategies.