Influence of calcium, magnesium and iron ions on the molecular mass of exoproteins during biogranulation

Abstract

In this study, we performed the qualitative analysis of exoproteins during granule formation in the presence or in the absence of cations. The staining of thin granule cryosections showed that nucleic acids, proteins, polysaccharides and calcium cations were the dominant components of the granules. Proteins are the structural components associated with calcium ions. We determined changes in the proteomic profile and tightly bound extracellular polymeric substances (EPS) of the slime. The exopolymeric matrix containing the proteins was extracted using the Dowex resin method. Proteomic profile was analysed by SDS-PAGE method (sodium dodecyl sulphate polyacrylamide gel electrophoresis) using Coomassie blue staining in the samples of the aerobic granule matrix formed in the presence of multivalent cations and compared with that of the aerobic granules cultivated without cations. The results indicate that the granule matrix is predominantly composed of large and complex proteins that are tightly bound within the granular structure. The tightly bound extracellular polymeric substances (TB-EPS) may play a role in improved mechanical stability of aerobic granules. In the supernatant fraction of the sludge, only a small amount of free proteins in the medium molecular mass range was detected. The protein with high molecular mass (≥ 116 kDa) produced in the reactors with added Ca2+. Ca2+ had a considerable regulatory influence on production of extracellular proteins during aerobic granulation.