Activity of glycosidases from freshwater heterotrophic microorganisms on the degradation of extracellular polysaccharide produced by Anabaena spiroides (cyanobacteria)

Abstract

The activity of specific glycosidases during the degradation of the extracellular polysaccharide (EPS) produced by Anabaena spiroides was determined using MUF-substrates (MUF-monosaccharides). Polysaccharide degradation was found to occur in a two-phase process. The first consisted of high enzymatic activity that consumed 41% of the EPS at a relatively high rate, while the second consumed the remaining polysaccharide (59%) at a slower rate. A transition phase from the higher to the slower degradation rates was marked by a replacement of bacterial populations from coccoid to bacillus cells. During the degradation process, the bacterial biomass increased with the decrease of EPS, as revealed by bacterial cell counts. The enzymatic activity detected through the substrates MUF-α-D- and MUF-β-D-glucoside was higher than that detected by other substrates tested. The remaining glycosides were MUF-α-L-rhamnopyranoside, MUF-β-D-galactoside, MUF-α-D- mannopyranoside, MUF-β-D-fucoside, MUF-β-D-mannopyranoside, MUF-α-L-arabinopyranoside, and MUF-β-L-fucoside. The fluorescence emitted by each MUF-substrate was proportional to the concentration of the corresponding monosaccharide in A. spiroides EPS. This demonstrates the susceptibility of EPS produced by A. spiroides to enzymatic attack by bacterial populations.