Characterisation of extracellular polymeric substances from different cyanobacterial species and their influence on biocalcification processes

Abstract

Environmental contextExtracellular polymeric substances provide a nucleation site for calcium carbonate and hence are important for bio-calcification processes, with implications for sediment formation and the global carbon cycle. We investigate the calcification potential of polymeric substances produced by five species of cyanobacteria. The results indicate that the protein content and alkaline functional groups of the extracellular polymeric substances may have a significant effect on cyanobacterial calcification. AbstractCyanobacterial calcification plays a crucial role in the formation of freshwater calcium carbonate precipitates, with cyanobacterial extracellular polymeric substances (EPSs) contributing significantly, partly by providing a nucleation site for calcium carbonate. Despite this, cyanobacterial EPS and their effect on calcification processes have not been completely characterised. In the present study, five cyanobacterial species were selected. First, EPS characteristics of these cyanobacterial species were examined, showing that proteins dominated both EPSs released in to solution (REPSs) and cell-surface bound (LEPSs). The major EPS functional groups included acidic groups, such as carboxyl groups, and highly alkaline groups, such as hydroxyl and amino groups. The calcification ability of different cyanobacterial species was found to vary dramatically. Solution pH increased during the calcification process, which was beneficial to the supersaturation of CaCO3, and could affect the calcification potential. Precipitation, however, was positively correlated with EPS protein content and the concentration of basic functional groups, such as amino or hydroxyl groups. These results suggest EPS protein content and alkaline functional groups may have a significant effect on cyanobacterial calcification. The results also provide a potential application in that EPS proteins of cyanobacteria may have beneficial positive applications in the removal of multivalent cations from wastewater.