Insight into c-di-GMP Regulation in Anammox Aggregation in Response to Alternating Feed Loadings

Substrate concentrations generally fluctuate in wastewaters. However, how anammox biomass behaves to overcome the stress of alternating feed loadings remains unclear. Here, we combined long-term reactor operation, batch tests, 16S rRNA transcript sequencing, and metabolomics analysis to investigate the aggregation of anammox biomass under the regulation of c-di-GMP, a key second messenger, in response to alternating feed loadings. We demonstrated that the aggregation process was significantly faster under alternating loadings and was significantly correlated with higher levels of c-di-GMP and extracellular polymeric substances (EPS) production. The increase in c-di-GMP was positively correlated with a higher relative transcript expression level in the c-di-GMP pathway-dependent community. The targeted metabolomics results indicated that the increased production of fructose 6-phosphate and UDP-N-acetyl-d-glucosamine, the precursor substances for the synthesis of exopolysaccharides, was induced by higher le...