Characterization of three carrageenases from marine bacterium Shewanella sp. LE8: A novel approach for producing ι-carrageenan oligosaccharides.

Carrageenan oligosaccharides have attracted significant attention due to their excellent biological activities, and they can be produced by carrageenases. In this study, a novel marine bacterium, Shewanella sp. LE8, was used to enzymatically degrade carrageenan, and the κ-, ι-, and λ-carrageenases produced by the bacterium were characterized. The crude enzyme derived from media exhibited κ-carrageenase activity, indicating its natural secretion during growth and proliferation. According to the results of molecular weight distribution from HPGPC, λ-carrageenan could be degraded by Shewanella sp. LE8 cells in both 20 mM Tris-HCl buffer and PBS, while ι-carrageenan can only be hydrolyzed in PBS environment, indicating the activation of ι-carrageenase in Shewanella sp. LE8 was dependent on the presence of Na ions. The components of carrageenan hydrolysates were determined by ESIMS, and results revealed that κ-carrageenan hydrolysates were primarily consisted of G4S-DA, [G4S-DA] and [G4S-DA], while ι-carrageenan hydrolysates were predominantly composed of [G4S-DA2S]. Moreover, the fragment ions of λ-carrageenan revealed that the hydrolytic process not only encompasses enzymatic cleavage of glycosidic bonds but also involves the participation of sulfatase. The precise structure was further elucidated through NMR analysis, confirming that the end-products of ι-carrageenase were neoι-carratetraose. The results highlight the potential of Shewanella sp. LE8 for industrial applications in the production of ι-carrageenan oligosaccharides.