Quorum sensing mediated cross-feeding determines the impaired denitrification under micro(nano)plastic stress within aerobic granular sludge systems

The accumulation of microplastics (MPs) and nanoplastics (NPs) in wastewater significantly hinders denitrification in biological wastewater treatment systems, yet the intrinsic mechanisms are not fully understood. Here, we combined signal molecule monitoring, electrochemical characterization and multi-omics analysis to investigate how quorum sensing (QS)-mediated cross-feeding influences the denitrification process in aerobic granular sludge systems. Results showed that after 90-day exposure to micro(nano)plastics, there witnessed a decline in the cross-talk between multiple signaling molecules (including AHLs, c-di-GMP and DSF), thereby disrupting the QS system to opportunely sense changes in the external environment. As a consequence of impaired QS, the expressions of downstream genes encoding metabolite synthesis pathways were comprised, resulting in limited cross-feeding of amino acids and cofactors among microorganisms. This resulted in a reduction in redox-active metabolites such as riboflavin and subsequently deteriorated the denitrification electron transfer process. Specifically, extracellular electron transfer capacity decreased to 88.08% (MPs) and 79.64% (NPs) compared to control group, while denitrification electron transfer chain activity dropped to 63.33% (MPs) and 63.75% (NPs). Therefore, the total nitrogen (TN) removal decreased to 69.47% (MPs) and 54.01% (NPs). Our findings provided the first profile of the crucial role of QS in regulating interspecies interaction (e.g., cross-feeding of public goods) and ultimately leading to a declined electron transfer process, uncovering the important mechanisms underlying the declined denitrification under micro(nano)plastic stress.