Abstract
D. Giroldo, A.A.H. Vieira and B.S. Paulsen. 2005. Microbial degradation of extracellular polysaccharides released by a tropical strain of Staurastrum orbiculare (Zygnematophyceae). Phycologia 44: 671–677.The extracellular polysaccharide (EPS) released by a freshwater desmid, Staurastrum orbiculare (Zygnematophyceae), was characterized and their degradation by heterotrophic microbial populations was also evaluated. The EPS was purified by anion exchange column chromatography, the monosaccharide composition was determined by gas chromatography and the linkages of the monosaccharides by gas chromatographic analysis coupled with electron impact mass spectrometry. The EPS was mainly eluted in one weak acid fraction, although a smaller strong acid fraction was also eluted. The two fractions had similar composition and both of them were mainly composed of fucose, glucuronic acid, galactose, galacturonic acid, xylose, glucose, rhamnose and N-acetyl glucosamine. We monitored the entire EPS degradation, and also their components separately, during 35 days using pulse amperometric detection in a high-performance liquid chromatography. Fucose, galactose and especially glucose showed a faster degradation pattern than rhamnose and arabinose, whereas xylose and the total EPS showed an intermediate degradation pattern. The entire EPS was degraded in about 14 days evidencing S. orbiculare EPS as a high quality carbon source to the natural bacterial community of Barra Bonita reservoir.
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