α-Carrageenan: An alternative route for the heterogenous phase degradation of hybrid ι-/κ-carrageenan

Abstract

Carrageenans are sulfated galactans densely packed in the cell wall of numerous red algae (Rhodophyta). The most abundant in algae and the most exploited industrially for their gelling properties are the κ- (kappa) and the ι- (iota)-carrageenans which the carrabiose repetition units are substituted by one or two sulfate ester groups. These polyanionic polysaccharides represent an important marine biomass and are carbon source for a number of marine bacteria. One polysaccharide utilization loci, a cluster of genes co-localized in the genome of the marine strain Paraglaciecola atlantica T6c, encompasses several glycoside hydrolases and sulfatases dedicated to the degradation of carrageenan. In addition to one ι-carrageenase and three carrageenan sulfatases, already characterized, we discovered the first endo-α-carrageenase and an exo-α-carrageenase sulfatase which allowed describing an alternate way to the degradation of ι-carrageenan without ι-carrageenase. α-Carrageenan didn't make gels in presence of salt suggesting that desulfation of ι-carrageenan probably helps to solubilize the gelling carrageenan. The degradation of the κ-carrageenan fraction of hybrid κ-/ι-carrageenan was also obtained without κ-carrageenase.