Novel insights on biofilm development in sewers: Cross-kingdom exchange of quorum-sensing signaling molecules

In sewers, biofilms are generated due to long-distance sewage transportation. However, the metabolism and reproduction of bacteria and fungi in biofilms and the mechanism of cross-kingdom exchanges mediated by quorum-sensing signaling molecules remain unclear. In this study, the distributions of bacteria and fungi communities in biofilms were investigated using high-throughput sequencing. The mechanism by which signaling molecules participate in biofilm development was explored through statistical analysis. The ecosystem operation mode featured by pollutant conversion, bacteria–fungi interaction (BFI), and cross-kingdom exchange of key signaling molecules in municipal sewers was clarified. The result showed that variations in C, N, and S pollutants in the sewer were related to BFI. Lactivibrio and Candida, key species generating signaling molecules in bacteria and fungi, significantly accelerated pollutant biodegradation and biofilm development. Additionally, a quantitative detection system was established for the signaling molecules. The average concentrations of C4-HSL, C10-HSL, and 3-oxo-C12-HSL (bacteria) were 0.25, 1.41, and 0.98 μg/L, respectively. Average concentrations of farnesol, tyrosol, and farnesoic acid signaling molecules were 10.04, 126.29, and 94.79 ng/L, respectively. Moreover, thickness and extracellular polymeric substances in different stages of biofilm development were explored. The results showed that acyl homoserine lactones dominated biofilm development, whereas signaling molecules of C. albicans had limited influences. The interaction of Pseudomonas aeruginosa and C. albicans dominated the cross-kingdom exchange between bacteria and fungi mediated by signaling molecules. This study reveals the characteristics of the interaction and metabolism of bacteria and fungi in sewers. It also provides theoretical references for social behaviors and the regulation of microbes in biofilms in sewers.