Methylisothiazolinone modulates community assembly and improves syntrophic cooperation via adaptive evolution during sludge anaerobic digestion

Various antimicrobials could pose multifaced threats to anaerobic digestion (AD) of waste-activated sludge (WAS), yet it is still unclear how antimicrobials would affect the metabolic activity and assembly process of anaerobic microbiome. In this study, a typical antimicrobial, methylisothiazolinone (MIT), was introduced in AD and induced an initial lag effect on methane production that was eventually recovered. Although MIT disintegrated WAS to promote the release of bioavailable substrates from extracellular polymeric substances (EPS), it also caused adverse stress to the microbiome. The initial microbial metabolic activities and syntrophic relationships associated with methane generation were distinctly inhibited. Because the self-adaptive systems of two-component systems (e.g., ddpF, and ddpD) and quorum sensing (e.g., cheR, and cydB) were activated to restore the syntrophic interaction among functional anaerobes, metabolic activities were gradually recovered for methane generation. Ultimately, the methane-generation species (e.g., Methanobacterium, and Methanomassiliicoccus) were driven as core species by deterministic processes, while non-functional species (e.g., Nitrospirota) were marginalized by stochastic processes under MIT stress. Overall, this finding indicated the intrinsic drive of evolutionary adaptation, unraveled the community assembly process at phylogenetic level under antimicrobial stress, and gave direction on the assessment and mitigation of external contaminant-related ecological risks in WAS treatment.