Bioflocculation effect of Glyptotendipes tokunagai on different Microcystis species: Interactions between secreted silk and extracellular polymeric substances

Cyanobacterial blooms are a major problem in many lakes and can negatively impact public health and ecosystem services. The bioflocculation technique has proven to be a cost-effective, environmentally friendly technique with no secondary pollution to harvest multiple microalgae; however, few studies have focused on its effect on and potential for controlling cyanobacterial blooms in eutrophic lakes. In this study, the bioflocculation efficiencies of different Microcystis species under Glyptotendipes tokunagai (Diptera, Chironomidae) stress conditions and the interactions between secreted silk from Chironomid larvae and extracellular polymeric substances (EPS) from Microcystis were compared. The results indicated that G. tokunagai presented better bioflocculation efficiency on M. wesenbergii than on M. aeruginosa. The formation of “Large Algal Aggregate” flocs was promoted by the derived-soluble extracellular polymeric substances (i.e., proteins and polysaccharides, sEPS) from M. wesenbergii and silk from G. tokunagai. Both M. wesenbergii and midge silk had abundant functional groups, which was beneficial to the formation of the large aggregate. G. tokunagai secreted a large amount of silk to bridge with the sEPS of M. wesenbergii, forming a network structure via interaction between filamentous substance (i.e., complex of sEPS and silk) that plays an important role in the aggregation of Microcystis and the removal of the Microcystis biomass in the water column. The findings provide further insights that will benefit the existing efforts of combating Microcystis blooms in the water column via bioflocculation and will provide a new sustainable approach for inhibiting early bloom formation from the perspective of its provenance in the sediment-water interface.