Metagenomic insights into microbial communities and antibiotic resistance in treated wastewater for urban irrigation.

BACKGROUND

The increasing reuse of treated wastewater for urban irrigation globally has raised ecological and public health concerns associated with microbial contaminations, antibiotic resistance genes (ARGs), and pathogen dissemination.

METHODS

Using a metagenomic approach, we analyzed microbial communities, ARGs, and pathogen profiles in three types of treated wastewater (W1, W2, W3) used for urban irrigation. Physicochemical properties, including nutrients and heavy metals, were also assessed to identify potential drivers of microbial and resistance patterns.

RESULTS

Significant variations in water quality and microbial community were observed across wastewater treatments. W2 showed the highest nutrient and organic pollution levels, while W3 exhibited elevated heavy metals such as zinc (83.37 µg/L), chromium (1.89 µg/L), and nickel (4.93 µg/L). Treated wastewater harbored significantly higher microbial diversity than tap water (P < 0.05), with W3 showing the most unique amplicon sequence variants (ASVs; 1 945, 7.31%). ARGs analysis revealed treatment-specific profiles: W1 was enriched in mupirocin and tetracycline resistance, W2 was dominated with beta-lactams and sulfonamides (P < 0.05), and W3 was enriched in fosfomycin and diaminopyrimidine resistance. Multidrug resistance genes dominated across all samples. PCoA revealed distinct microbial and ARGs structures across treatments (P < 0.05). Pathogens such as Salmonella enterica and Pseudomonas aeruginosa were abundant in treated wastewater, with Escherichia coli and Staphylococcus aureus identified as key pathogen hubs in ARG-pathogen co-occurrence networks. Nutrients (total nitrogen, phosphorus) and heavy metals (Fe and Pb) were key drivers of microbial community composition, ARGs abundance and pathogen prevalence.

CONCLUSIONS

This study underscores the ecological risks of using treated wastewater in urban environment, particularly due to the persistence of ARGs and pathogenic bacteria. Targeted removal of nutrients and heavy metals during wastewater treatment could help reduce microbial and resistance-related contamination, improving the safety of treated wastewater reuse.