Production of extracellular polymeric substances (EPS) by benthic diatoms: effect of irradiance and temperature

Abstract

An axenic culture of Cylindrotheca closterium and a natural community of benthic diatoms were used to study the effect of temperature and irradiance on the production of extracellu- lar polymeric substances (EPS). In the culture, results depended on the growth stage of the algae and on whether absolute values or biomass-related values were considered. The highest amount of EPS (standing stock) was produced at 15 and 25°C during early stationary growth phase. When EPS con- centrations were normalized to chlorophyll a (chl a), maximum values were measured at 4 and 10°C. Independent of temperature the ratios (EPS:chl a) decreased with increasing age of the culture. Addi- tionally, differences between the investigated temperatures were less pronounced in older cultures. A field sample of benthic diatoms was used to study: (1) the combined effect of temperature and irra- diance on primary production and excretion of EPS; and (2) the partitioning of photosynthetically fixed carbon (C) into different fractions of intracellular and extracellular C pools by using a short- term 14 C incorporation. Again highest values of primary production and EPS (production rates) were measured at 25°C. At lower irradiances, the temperature of 35°C had an inhibitory effect on the pro- duction rates of all fractions. In the culture as well as in the natural sample, the fraction of EPS that was closely bound to the cells (attached EPS) and the soluble fraction (colloidal EPS) were produced in different amounts at the different temperatures. This suggested that the production of the 2 oper- ationally defined fractions of EPS might serve different functions, e.g. for migration or for storage of reserve products.