Produção de exopolissacarídeos em diferentes fases do crescimento de Staurastrum tohopekaligiensis Wolle (Chlorophyceae)

Abstract

Laboratory experiments were carried out with the aim of studying the production of dissolved and capsular exopolysaccharides in diíFerent growth ages by Staurastrum tohopekaligiensis Wolle. This microalga was isolated from a marginal lagoon of the Mogi- Guaçu River, SP-Brazil. The cells were grown axenically in artificial culture médium under controlled conditions of light intensity, temperature, aeration and light/dark cycle. After 25 and 48 days of growth, the cells were harvested by centrifligation, washed with distilled water by centrifiigation, resuspended in distilled water, and submitted to 40 0C under mixing with a magnetic stirrer to extract the capsules. The capsular material and the dissolved one were both filtered, concentrated, dialyzed and ffeeze-dried. The production of exopolysaccharides was greater in the stationary growth phase than in the exponential one. Gel filtration chromatography analysis revealed that both the capsular and the extracellular polysaccharides obtained at different growth ages can be ífactioned in two fractions, "A" and "B". Fraction "A" presented a molecular weight close to or larger than 2 x 106 daltons, while fraction "B" of 2 x IO6 daltons, approximately. lon exchange chromatography data showed great similarities between capsular polysaccharide and extracellular polysaccharide, both having acid nature. When different growth ages are considered, a significant variation was observed in relation to the percentual participation of fractions "A" and "B" of the capsular polysaccharide. It was observed that fraction "B" from "old" cultures represents 92% of the total. Biochemical analysis revealed that the extracellular material does not have a sulphate group but has a proteic fraction. Gas chromatography analysis of extracellular and capsular polysaccharides revealed the presence of neutral sugars and acid sugars. The neutral sugars are; flicose, galactose, glucose, mannose, rhamnose, arabinose and 3-O-methyl galactose and the acid ones are: galacturonic acid and glycuronic acid.