Comprehensive analysis of effects of magnetic nanoparticles on aerobic granulation and microbial community composition: From the perspective of acyl-homoserine lactones mediated communication

N-acyl-homoserine-lactones as a critical factor for biofilm formation during the initial adhesion stage in drinking water distribution systems

The N-acyl-homoserine-lactone (AHLs)-mediated quorum sensing (QS) system is crucial for the coordination of microbial behaviors within communities. However, the levels of AHLs in biofilms in drinking water distribution systems (DWDSs) and their impact on biofilm formation remain poorly understood. Herein, we simulated DWDSs via biofilm reactors to explore the presence and influence of AHLs during the initial stages of biofilm formation on pipe walls. Glass, polypropylene random copolymer (PP-R) and stainless steel (SS) were used as the coupon materials and the three parallel experimental groups were set up and named accordingly. The glass material is considered to form biofilms only minimally and is therefore used as a negative control. By day 30, the concentration of AHLs in biofilm phase in both PP-R group and SS group reached 1200-1800 ng/L. The predominant AHLs were C6-HSL, C8-HSL, and C10-HSL, with a significant positive correlation between AHLs and biofilm biomass. Metagenomic analysis revealed that microbes exhibiting significant differences among the three groups all demonstrated notable correlations with AHLs. Subsequent analysis of QS genes revealed that the genes associated with AHLs biosynthesis and QS receptors were more abundant in the PP-R and SS groups with biofilm formation. Additionally, we analyzed the abundance of genes related to cell motility, transmembrane transport, tricarboxylic acid cycle, and genetic information synthesis. The co-occurrence network indicates that these processes exhibit a strong correlation with QS genes. This study demonstrates the pivotal role of AHLs in microbial communication during the initial stages of biofilm formation in DWDSs and indicates that the regulatory pathways and mechanisms of AHLs may vary under different environmental conditions.

Effects of nanoparticles on anaerobic, anammox, aerobic, and algal-bacterial granular sludge: A comprehensive review

Nanoparticles (NPs) are of significant interest due to their unique properties, such as large surface area and high reactivity, which have facilitated advancements in various fields. However, their increased use raises concerns about environmental impacts, including on wastewater treatment processes. This review examines the effects of different nanoparticles on anaerobic, anammox, aerobic, and algal-bacterial granular sludge used in wastewater treatment. CeO2 and Ag NPs demonstrated adverse effects on aerobic granular sludge (AGS), reducing nutrient removal and cellular function, while anaerobic granular sludge (AnGS) and anammox granular sludge (AxGS) showed greater resilience due to their higher extracellular polymeric substance (EPS) content. TiO2 NPs had fewer negative effects on algal-bacterial granular sludge (ABGS) than on AGS, as algae played a crucial role in enhancing EPS production and stabilizing the granules. The addition of Fe3O4 NPs significantly enhanced both aerobic and anammox granulation by reducing granulation time, promoting microbial interactions, improving granule stability, and increasing nitrogen removal efficiency, primarily through increased EPS production and enzyme activity. However, Cu and CuO NPs exhibited strong inhibitory effects on aerobic, anammox, and anaerobic systems, affecting EPS structure, cellular integrity, and microbial viability. ZnO NPs demonstrated dose-dependent toxicity, with higher concentrations inducing oxidative stress and reducing performance in AGS and AnGS, whereas AxGS and ABGS were more tolerant due to enhanced EPS production and algae-mediated protection. The existing knowledge gaps and directions for future research on NPs are identified and discussed.

Biochar inoculated with Rhodococcus biphenylivorans altered microecological regulation by promoting quorum sensing and electron transfer: Up-regulation of related genes and enhancement of phenol and ammonia degradation

Bioaugmentation is an efficient method for improving the efficiency of coking wastewater removal. Nevertheless, how different immobilization approaches affect the efficiency of bioaugmentation remains unclear, as does the corresponding mechanism. With the assistance of immobilized bioaugmentation strain Rhodococcus biphenylivorans B403, the removal of synthetic coking wastewater was investigated (drying agent, alginate agent, and absorption agent). The reactor containing the absorption agent exhibited the highest average removal efficiency of phenol (99.74 %), chemical oxygen demand (93.09 %), and NH4+-N (98.18 %). Compared to other agents, the covered extracellular polymeric substance on the absorption agent surface enhanced electron transfer and quorum sensing, and the promoted quorum sensing benefited the activated sludge stability and microbial regulation. The phytotoxicity test revealed that the wastewater's toxicity was greatly decreased in the reactor with the absorption agent, especially under high phenol concentrations. These findings showed that the absorption agent was the most suitable for wastewater treatment bioaugmentation.