Partial characterisation of exopolysaccharides exudated by planktonic diatoms maintained in batch cultures

Abstract

Abstract Axenic cultures of the marine planktonic diatoms Navicula directa (W. Smith) Ralfs, Amphora holsatica Hustedt and Melosira nummuloides (Dillwyn) Agardh, isolated from samples from the Ria de Aveiro, Portugal, were successfully established. For each culture, the extracellular carbohydrate production was related to the growth curve and nutrient concentration (NO3– and PO43–) in the culture medium. Analysis by gas-liquid chromatography and Fourier transform infrared spectroscopy (FT-IR) was performed on the exopolysaccharides isolated from the culture medium. It was concluded that the three marine diatoms produced and exudated different amounts of carbohydrates, and that the exudation process was more important when the media were almost nutrient depleted, and also when the species reached the stationary growth phase. The exopolysaccharides produced by the three species, mainly polymers of uronic acids, were very similar. However, the results obtained from gas-liquid chromatography suggest that differences in the composition of neutral sugars may occur. The FT-IR spectra support the results of chemical analysis.