Metagenomic analysis reveals indole signaling effect on microbial community in sequencing batch reactors: Quorum sensing inhibition and antibiotic resistance enrichment

Indole is an essential signal molecule in microbial studies. However, its ecological role in biological wastewater treatments remains enigmatic. This study explores the links between indole and complex microbial communities using sequencing batch reactors exposed to 0, 15, and 150 mg/L indole concentrations. A concentration of 150 mg/L indole enriched indole degrader Burkholderiales, while pathogens, such as Giardia, Plasmodium, and Besnoitia were inhibited at 15 mg/L indole concentration. At the same time, indole reduced the abundance of predicted genes in the signaling transduction mechanisms pathway via the Non-supervised Orthologous Groups distributions analysis. Indole significantly decreased the concentration of homoserine lactones, especially C14- HSL. Furthermore, the quorum-sensing signaling acceptors containing LuxR, the dCACHE domain, and RpfC showed negative distributions with indole and indole oxygenase genes. Signaling acceptors' potential origins were mainly Burkholderiales, Actinobacteria, and Xanthomonadales. Meanwhile, concentrated indole (150 mg/ L) increased the total abundance of antibiotic resistance genes by 3.52 folds, especially on aminoglycoside, multidrug, tetracycline, and sulfonamide. Based on Spearman's correlation analysis, the homoserine lactone degradation genes which were significantly impacted by indole negatively correlated with the antibiotic resis-tance gene abundance. This study brings new insights into the effect of indole signaling on in biological wastewater treatment plants.

Automated summary

Indole is found to have an influence on the microbial communities in biological wastewater treatments. It enriched indole degrader Burkholderiales and inhibited pathogens at different concentrations. Indole also affected the abundance and distribution of genes in signaling transduction mechanisms pathway and quorum-sensing signaling acceptors. Moreover, it increased the abundance of antibiotic resistance genes, especially aminoglycoside, multidrug, tetracycline, and sulfonamide.