"Iota/kappa Carrageenans and Agarans from Gymnogongrus tenuis (Phyllophoraceae, Rhodophyta)

CIANCIA, M.; CANELON,D; PEREZ RECALDE MERCEDES; SUAREZ A; COMPAGNONE R; MATULEWICZ, M C; CEREZO, A

Florianopolis

Congreso; IV CLABA (Congreso Latinoamericano de Biotecnología de Algas); 2013

Seaweeds from the genus Gymnogongrus are know to produce kappa/iota-carrageenans with predominance of iota-structure1. However, it was found that galactans from G. tolulosus comprise also important quantities of agarans with an unusual substitution pattern, including important quantities of alfa-L-galactose 3-sulfate units2,3. Vegetative thalli from Gymnogongrus tenuis (J. Agardh) J. Agardh, collected in Puerto Maya, Estado Aragua, Venezuela, were extracted with methanol and the residue was further extracted with water at room temperature and at 90ºC giving extracts A1 and A2, and C1, respectively (yields, 0.6 and 0.3, and 47.7 % of the milled seaweed). Enantiomeric analyses showed that A1 and A2 are mostly agarans, while C1 is composed mainly by carrageenans, only traces of agarans were detected. Structural analysis of the latter extract (molar ratio carbohydrate:sulfate, 1.00:1.04), showed the presence of 1/3 of precursor units, with predominance of iota/nu-carrageenan diads. Fractionation of C1 with KCl gave nine fractions; the major fraction, F4 (43.3 % of C1, carbohydrate:sulfate, 1.00:1.05) precipitated at 0.3-0.6 M, and another important fraction, F9, remained soluble in 4.3 M KCl (14.7 %. carbohydrate:sulfate, 1.00:1.18). All these fractions showed by chemical and spectroscopic analyses, iota/kappa-structures; only minor quantities of agarans were detected. On the other hand, extracts A1 and A2 (molar ratio carbohydrates:sulfate 1.00:0.72 and 1.00:0.68, respectively) comprise only small amounts of iota-carrageenans (15 %). The other structures present correspond to agarans, with 3-linked beta-D-galactose units partially substituted on C-6 and 4-linked 3,6-anhydro-alfa-L-galactose and 3-substituted alfa-L-galactose residues, as found before in G. torulosus, being these substituents, sulfate ester groups and single stubs of beta-D-xylose in comparable quantities. These results show that Gymnogongrus tenuis biosynthesizes important amounts of iota/kappa-carrageenans, being a potential source of hydrocolloids, but also small quantities of interesting agaran structures that seem to be independent polymer molecules.