Wastewater Composition Impacts the Microbial Community Assembly, Influent Immigration and Antimicrobial Resistance in Activated Sludge Systems

• Main Author: Mendoza, Emmanuel Díaz
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2023
• Subjects: Analytical chemistry; Antibiotics; Antimicrobial agents; Bacteria; Bioengineering; Biogeochemistry; Chemical oxygen demand; Drug resistance; Ecosystems; Effluents; Environmental engineering; Environmental impact; Environmental management; Enzymes; Genes; Genetic engineering; Genetics; Immigration; Microbiology; Microorganisms; Nutrient removal; Oxidation; Pathogens; Pharmaceutical sciences; Pharmacology; Plasmids; Pollutants; Reactors; Rivers; Sludge; Water treatment
• ISBN: 9798382616513

Wastewater Treatment Plants (WWTPs) are believed to be a propagator of Antimicrobial Resistance Genes (ARGs) in the environment. However, the complex dynamics impacting ARG persistence in activated sludge are still not well understood. The present study investigated variations in microbial community compositions and the complement of ARGs they carried using bench-scale activated sludge systems receiving synthetic wastewater of two different compositions. The first synthetic wastewater composition was more readily biodegradable and rich in sugars whilst the other was slowly biodegradable and rich in proteins and lipids. These systems were supplied with influent solids from the sewers to simulate immigration from upstream sewer systems. Amplicon sequencing of the 16S rRNA gene revealed that the microbial communities in reactors receiving the slowly degradable synthetic wastewater was more diverse and exhibited higher rate of immigration than the community in reactors receiving the readily degradable wastewater. The nitrate production was also found to be influenced by wastewater composition with the slowly biodegradable composition promoting the growth of Nitrosospira, a low rate ammonia oxidizing bacterial genus. A qPCR approach to quantify ARGs found that, out of the 81 genes evaluated, 17 genes had a significantly higher concentration in the slowly biodegradable composition, whilst the readily biodegradable composition showed a significantly higher concentration in 9 genes. Immigration significantly increased the concentrations of 8 genes and decreased the concentration of 4 genes. Analysis of ARG sequence variants revealed evidence of direct immigration in only one gene (betOMPK). The remaining targeted genes were likely impacted by an ecological shift in the community composition. The data from the sequence variant analysis for the remaining genes were, unfortunately, inconclusive. Taken together, this study suggests that a more diverse community growing on slowly degradable substrates is more receptive to continuous immigration than a less diverse community growing on readily degradable substrates. Furthermore, the chemical wastewater composition and immigration influence the prevalence of ARGs carried by activated sludge communities. The diversity of the microbial community in activated sludge positively correlates with the diversity of ARGs