Glucose uptake and extracellular polysaccharides (EPS) produced by bacterioplankton from an eutrophic tropical reservoir (Barra Bonita, SP–Brazil)

We have studied the production of polysaccharides by bacterioplankton in an eutrophic tropical reservoir (Barra Bonita, SP–Brazil) through a decay experiment using glucose as carbon source. The temporal evolution was monitored by measuring the total organic carbon and the contents of monosaccharides. The glucose added to the reservoir sample water was consumed at higher rates within the first hours of incubation, and after 30 days 94.4% of the carbon contents were mineralized; 4.2% remained as particulate organic carbon (POC) form and 1.5% as dissolved organic carbon (DOC) form. The production of polysaccharides occurred in two stages: within the first 48 h, there was intense glucose consumption with small POC increment (ca. 16%) and release of small quantities of dissolved polysaccharide. In the second, more intense stage production was accelerated after the 9th day of incubation, with the highest polysaccharide concentration measured on the 20th day. Such formation of polysaccharides was related to the excretion of capsules and sheaths by bacterioplankton, mainly in the senescence of heterotrophic populations, with release of reserve and structural intracellular materials.