This study constructed MiDAS 4, a comprehensive 16S rRNA gene database from 740 WWTPs worldwide, enabling species-level identification of activated sludge microbiota. It found that despite vast overall microbial diversity, a small number of core and conditionally rare/abundant taxa dominate globally, shaped by factors like process type and temperature, suggesting functional redundancy and potential for transferring research findings across regions.

The MiDAS Global Consortium includes members affiliated with universities, research institutions, and private companies involved in wastewater treatment (e.g., Veolia Water Technologies AB). While this collaboration provides valuable expertise and access to diverse samples, it could potentially introduce bias in data interpretation or emphasis on certain technologies.

This is a valuable study with a large-scale global sampling effort and high taxonomic resolution, providing a much-needed resource for the field. However, the limitations regarding unclassified taxa, potential confounding factors, and primer bias prevent a rating of 5.