Formation of transparent exopolymer particles, TEP, from dissolved precursor material

Transparent exopolymer particles (TEP) form from polysaccharides released by many phytoplankton species, but this process by which dissolved organic matter becomes particulate is poorly understood. Here, the abiotic formation of TEP from precursors <0.2 mu m and the minimum molecular weight (MW) of TEP-precursors were studied. In most samples TEP formed from material <0.2 mu m (polycarbonate membrane filters, Poretics) when exposed to laminar shear in Couette flocculators. This result was unexpected as no TEP formed from material <0.45 mu m (polycap capsules, Whatman) due to surface coagulation onto bubbles (Zhou et al. 1998; Limnol Oceanogr 43:1860-1871). Some TEP-precursors were able to pass through dialysis bags with a nominal pore size of 8 kDa (natural cellulose, Spektrum), although their MW is presumably 2 orders of magnitude larger, suggesting that TEP-precursors can be fibrillar. It is suggested that freshly released precursors are fibrillar and that these fibrillar precursors form larger colloids and eventually TEP within hours to days after their release.