engleski

Nanoscale visualization of Extracellular Polymer Release by Marine Diatom Cylindrotheca fusiformis

AFM has already proven useful as a technique for investigating structural and mechanical properties of the diatom extracellular polymer substance of which polysaccharides are the primary component. Extracellular polymer substance is defined as any macromolecule secreted external to the cell wall that may stay attached or be released to the environment. Direct visualization of extracellular polymer molecules and of their supramolecular organization has not been achieved before. We selected Cylindrotheca fusiformis (the planktonic, raphid, motile marine diatom) to investigate extracellular polymers at the time of their release and their capacity for supramolecular organization using experimental procedure adopted for AFM imaging of the marine gel phase. Cylindrotheca spp. are considered the main exudates producers in the shallow northern Adriatic Sea and may be associated with the formation of an enigmatic gel phase in this marine system. We show that the carboxylated and sulfonated polysaccharides produced by single Cylindrotheca fusiformis cell form a nanoscale structured material. The structure consists of a web or tangle of strings up to 900 nm in length that are 0.7 to 0.9 nm thick, interconnecting beads 2.5 to 12 nm in diameter. The beads may have a protein core that allows efficient intracellular packing of negatively charged polysaccharide fibrils and may serve the diatoms as nucleation centers for silica precipitation when excreted.

AFM; Cylindrotheca fusiformis; EPS

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