Recebido em 6/5/11; aceito em 1/11/11; publicado na web em 4/1/12 CHEMICAL CHARACTERIZATION OF THE GELS PRODUCED BY THE DIAZOTROPHIC BACTERIA Rhizobium tropici AND Mesorhizobium sp. The exopolysaccharides with characteristics of gel produced by Rhizobium tropici (EPS RT) and Mesorhizobium sp (EPS MR) are acidic heteropolysaccharide composed mainly of glucose and galactose in a molar ratio of 4:1 and 5:1 respectively, with traces of mannose (~ 1%). Chemical analysis showed the presence of uronic acid, pyruvate and acetyl-substituents in the structures of both polymers. Experiments of gel permeation chromatography and polyacrylamide gel electrophoresis showed that EPS RT and EPS MR are homogeneous molecules with low grade of polydispersity. The EPS were characterized using spectroscopic techniques of FT-IR, 1 H and 13 C-NMR.

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A fucomannogalactan from Rhizoctonia solani biomass was obtained after hot aqueous extraction and purified by freeze-thaw cycles and gel filtration chromatography on Sepharose CL-6B. The polysaccharide was homogeneous after HPSEC/RID analysis (M/M~1.1), displaying an average molecular weight of 15.4×10Da. Its chemical structure was determined by methylation analysis (GC/MS) and spectroscopy (FTIR, 1D and 2D NMR). The polysaccharide had a branched α-1,6-linked Galp backbone with 66% linear residues, a number of which were at O-3 methylated. Side chains (34%) were always linked at O-2 positions of the main chain and consisted of single, non-reducing ends of α-d-Manp (6%) and α-l-Fucp (28%). Analysis of its biological activity showed that the highly purified fucomannogalactan from R. solani inhibited the proliferation of colon cancer cells in vitro, but that it did not have the same activity against lung cancer cells.