Metabolic network analysis reveals microbial community interactions in anammox granules

TLDR

Microbial communities mediating anaerobic ammonium oxidation (anammox) are energy‑efficient for nitrogen removal from wastewater, yet the functional role of heterotrophic bacteria in anammox granules remains poorly understood. The study aims to recover draft genomes of anammox and heterotrophic bacteria from a laboratory‑scale bioreactor using genome‑centric metagenomics. Metabolic network reconstruction and metatranscriptomics were applied to assess gene expression and potential interactions between anammox and heterotrophic bacteria. Chlorobi‑affiliated bacteria act as active protein degraders, recycling nitrate to nitrite, while other heterotrophs scavenge anammox‑produced detritus and peptides and may use H₂, acetate, or formate as electron donors, providing the first transcriptional insights into metabolic interactions within anammox granules.

Abstract

Abstract Microbial communities mediating anaerobic ammonium oxidation (anammox) represent one of the most energy-efficient environmental biotechnologies for nitrogen removal from wastewater. However, little is known about the functional role heterotrophic bacteria play in anammox granules. Here, we use genome-centric metagenomics to recover 17 draft genomes of anammox and heterotrophic bacteria from a laboratory-scale anammox bioreactor. We combine metabolic network reconstruction with metatranscriptomics to examine the gene expression of anammox and heterotrophic bacteria and to identify their potential interactions. We find that Chlorobi-affiliated bacteria may be highly active protein degraders, catabolizing extracellular peptides while recycling nitrate to nitrite. Other heterotrophs may also contribute to scavenging of detritus and peptides produced by anammox bacteria, and potentially use alternative electron donors, such as H 2 , acetate and formate. Our findings improve the understanding of metabolic activities and interactions between anammox and heterotrophic bacteria and offer the first transcriptional insights on ecosystem function in anammox granules.