Visual signal sensor coupling to nitrification for sustainable monitoring of trichloroacetaldehyde and the response mechanisms.

In this work, a toxicity monitoring microbial system (TMMS) with a nitrifying biofilm as a sensing element and cathode oxygen reduction as an electrical signal was successfully constructed for trichloroacetaldehyde (TCAL) detection. The current and nitrification rate showed a linear relationship with TCAL concentration from 0 to 100 µg/L (R2current = 0.9892, R2nitrification = 0.9858), indicating that the target substrate concentration can be directly obtained from an electrical signal without further sample concentration. High-throughput sequencing revealed that the TMMS was composed of autotrophic/heterotrophic nitrifying and denitrifying microorganisms. Further analysis via a symbiotic relationship network demonstrated that unclassified_Comamonadaceae and unclassified_Xanthobacteraceae were the core nodes for maintaining the interaction between autotropic and heterotrophic nitrifying bacteria. Kyoto Encyclopedia of Genes and Genomes analysis showed that the electron transfer process primarily relied on ferredoxin and cytochromes under TCAL stress, and the abundance of functional enzymes involved in the process of nitrification was decreased, resulting in changes in electrical signal output. This work explored a visual signal sensor combined with electrochemistry and autotrophic/heterotrophic nitrification, which provided new insights into recognition and response mechanisms for microbial monitoring of toxic substances.