Diversity and physiology of abundant Rhodoferax species in global wastewater treatment systems

Wastewater treatment plants rely on complex microbial communities for bioconversion and removal of pollutants, but many process-critical species are still poorly investigated. One of these genera is Rhodoferax, an abundant core genus in wastewater treatment plants across the world. The genus has been associated with many metabolic traits such as iron reduction and oxidation and denitrification. We used 16S rRNA gene amplicon data to uncover the diversity and abundance of Rhodoferax species in Danish and global treatment plants. Publicly available metagenome-assembled genomes were analyzed based on phylogenomics to delineate species and assign taxonomies based on the SeqCode. The phylogenetic analysis of "Rhodoferax" revealed that species previously assigned to Rhodoferax in wastewater treatment plants should be considered as at least eight different genera, with five representing previously undescribed genera. Genome annotation showed potential for several key-bioconversions in wastewater treatment, such as nitrate reduction, carbohydrate degradation, and accumulations of various storage compounds. Iron oxidation and reduction capabilities were not predicted for abundant species. Species-resolved FISH-Raman was performed to gain an overview of the morphology and ecophysiology of selected taxa to clarify their potential role in global wastewater treatment systems. Our study provides a first insight into the functional and ecological characteristics of several novel genera abundant in global wastewater treatment plants, previously assigned to the Rhodoferax genus.