Polissacarídeos extracelulares e atividade enzimática das glicosidases no reservatório de Barra Bonita, SP, Brasil
Abstract
Release of extracellular polysaccharides can occur from healthy and active cells
and has been demonstrated to be an important carbon source for bacteria. In eutrophic
environments where large blooms are formed by efficient extracellular polysaccharide
producers such as Microcystis aeruginosa and Anabaena spiroides, these organic materials
(high molecular weight extracellular polysaccharides) may support planktonic
bacterial growth. The aim of this study was to evaluate the extracellular glycolytic
enzyme activity during a seasonal cycle and a possible regulation of the corresponding
enzymes in response to variation of polysaccharides in Barra Bonita Reservoir. The
majority of enzymes exhibited a significant decrease during the dry season (April to
September). The content of total dissolved carbohydrates varied from 0.5 to 6.83 mg L-1
and was mainly (92%) constituted by polysaccharides. Phytoplanktonic community
showed a marked succession with cyanobacteria typically dominating during the rainy
season (Microcystis sp, Microcystis aeruginosa and Anabaena spiroides), whereas diatoms
(mostly Aulacoseira granulata) and cryptophytes (Cryptomonas sp) were dominant
through the dry season. Four algal blooms were observed during the experimental
period, and after each bloom the release of combined carbohydrates was followed by
high enzymatic activities, thus the production of extracellular enzymes for
microheterotrophic microorganisms was related to the influx of polymeric organic
substances. Even the monosaccharides composition of reservoir samples after each
bloom roughly revealed the extracellular polysaccharide composition of dominant
phytoplanktonic population. Experiments of polysaccharide degradation from Barra
Bonita Reservoir and produced by dominant phytoplanktonic organisms (A. granulata
e M. aeruginosa) assayed in laboratory conditions had confirmed the interpretation of
data measured in field.