Biogeochemical cycling processes associated with cyanobacterial aggregates

In natural freshwater and low-salinity waters, bloom-forming cyanobacteria often live in the form of cyanobacterial aggregates. Many heterotrophic bacteria colonize in the cyanobacterial aggregates, subsequently they constitute the fundamental unit with unique ecological functions. Compared with single-celled cyanobacteria, cyanobacterial aggregates exhibit many unique characteristics, e.g., rich organic matter, steep redox gradient, and complex inter-specific interactions. These properties enable cyanobacterial aggregates to become the hotspot for elemental biogeochemical cycling in aquatic ecosystems. Meanwhile, the inter-specific interactions within cyanobacterial aggregates are far more intense compared to those between single-celled algae and free-living bacteria. This review introduces current research progress on these aspects, with a focus on the biological, physiological and chemical processes within cyanobacterial aggregates, and discusses the micro-mechanisms of the macro-phenomena. In the future, the omic research of cyanobacterial aggregates and the construction of multi-omic microecological databases may become the key for exploring life processes within cyanobacterial aggregates and for revealing the mechanisms of cyanobacterial bloom outbreak.