Microalgae inoculation increases bacterial diversity and gene abundances related to nutrient removal while decreasing antibiotic resistant genes in municipal wastewater

Monitoring the interactions between microalgae and microbiomes, particularly in the context of nutrient and antibiotic resistance genes (ARGs) removal from municipal wastewater treatment system, is highly recommended for the environment and public health. This study evaluated the synergistic potential of microalgae-bacteria consortia in enhancing nutrient removal and mitigating ARGs in a lab-scale microalgal municipal wastewater treatment system. Three treatments were evaluated: the two individual microalgal strains (Tetradesmus obliquus and Chlorella sorokiniana) and their mixtures (1:1). All treatments showed high removal efficiencies for phosphates (>90 %; p < 0.001), nitrates (>80 %, p < 0.001), ammonia (>90 %, p < 0.0004) and chemical oxygen demand (COD) (>65 %, p < 0.008), significantly improving water clarity and quality. Microbiome analyses revealed that microalgal inoculation altered bacterial community diversity, structure and function. Functional metagenomic profiling showed a significant enrichment (p < 0.05) of genes associated with nitrogen and phosphorus metabolism in microalgal treatment groups compared to the untreated control. Resistome analysis indicated that raw wastewater harbored a high abundance of ARGs, which were significantly reduced following microalgal treatment (p < 0.0001). Overall, our findings demonstrate a mutually beneficial interaction between microalgae and the wastewater microbiome, where microalgae-induced changes increase bacterial diversity and functional gene abundance involved in nutrient and ARG removal. These results underscore the potential of microalgae-microbiome-based systems as an effective and sustainable solution for the removal of emerging contaminants, including nutrients, ARGs and pathogens from municipal wastewater.