Effects of different types of extracellular polysaccharides isolated from cyanobacterial blooms on the colony formation of unicellular Microcystis aeruginosa
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In this study, two types of extracellular polysaccharides (EPS), namely, mixed EPS (MX-EPS) and tightly bound EPS (TB-EPS), were extracted from cyanobacterial blooms using different methods. To evaluate their compositional differences, elemental composition, FTIR, and TG/DTA profile were measured for both EPS samples. Following that, unicellular Microcystis aeruginosa was cultured in a medium containing EPS, Ca2+ ion, and Mg2+ ion, and the effect of each type of EPS on the colony formation of M. aeruginosa was examined. Results showed that TB-EPS had more carboxy groups than MX-EPS, and that the TB-EPS medium contained Ca2+ and Mg2+ ions. These cations were not detected in the MX-EPS medium. During the colony formation experiment, colonies were observed when Ca2+ and Mg2+ ions were present at 250 mg/L concentration each. In addition, colony density increased when TB-EPS was added, compared to that of MX-EPS. Colonies were also observed in the medium containing only TB-EPS (100 mg/L), indicating that M. aeruginosa can form colonies using Ca2+ ion present in TB-EPS. During the MX-EPS extraction, Ca2+ ion chelated with EDTA was removed during ethanol precipitation. Therefore, the extraction protocol followed for TB-EPS was better than that of MX-EPS for maintaining Ca2+ ions, and thereby maintaining an EPS composition that enables for colony formation.
KeywordsCyanobacterial blooms Microcystis aeruginosa Extracellular polysaccharides (EPS) Cation Extraction Colony formation
The authors would like to extend deep gratitude to Prof. Dr. Fumio Imazeki, Safety and Health Organization, Chiba University, for the encouragement of this study.
This work was partially supported by JFE 21st Century Foundation and by the Japan Society for the Promotion of Science (JSPS) under a Grant-in-Aid for Scientific Research (C) (No. 18 K04404).
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