engleski

AFM imaging of extracellular polymer release by marine diatom Cylindrotheca closterium

Here we address a ubiquitous marine diatom Cylindrotheca closterium, isolated from Northern Adriatic seawater samples (surface water) and its extracellular polymer substance (EPS) at the single cell level using atomic force microscopy (AFM). Visualization of supramolecular organization of diatom EPS release is a key step towards understanding the relationship that links diatom EPS release and large scale phenomenon of gel formation in the northern Adriatic Sea. We have developed a simple procedure for AFM imaging of C. closterium cells on mica substrates in air and succeeded in imaging polysaccharide fibrils of the EPS. In logarithmic growth phase we visualized almost no EPS release, while during stationary growth phase EPS was found on approximately 25 % cells. Polysaccharide fibrils were mainly extending from cell's rostra and seemed attached to cells. Single fibrils and three dimensional networks of fibrils were also found free in bulk culture medium. We compared extracellular fibrils with structure of biofilm formed on mica sheets, left at the bottom of conical flasks with C. closterium culture and with purified exopolysaccharides, isolated from C. closterium culture medium. Biofilm appeared as a gel structure, with repeating number of pores between fibrils while isolated exopolysaccharides were present both as single fibrils and as networks, depending on concentration used for sample preparation. Similarity in height range profiles and in supramolecular organization is notable. The network pattern of EPS released by C. Closterium could prove crucial for understanding the giant gel formation in the Adriatic Sea.

marine diatom; Cylindrotheca closterium; Ceratoneis closterium; extracellular polymer substance; polysaccharides; atomic force microscopy; Adriatic Sea

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