To gel or not to gel: differential expression of carrageenan-related genes between the gametophyte and tetasporophyte life cycle stages of the red alga Chondrus crispus.

Chondrus crispus is a marine red alga with sulfated galactans, called carrageenans, in its extracellular matrix. Chondrus has a complex haplodiplontic life cycle, alternating between male and female gametophytes (n) and tetrasporophytes (2n). The Chondrus life cycle stages are isomorphic; however, a major phenotypic difference is that carrageenan composition varies significantly between the tetrasporophytes (mainly lambda-carrageenan) and the gametophytes (mainly kappa/iota-carrageenans). The disparity in carrageenan structures, which confer different chemical properties, strongly suggests differential regulation of carrageenan-active genes between the phases of the Chondrus life cycles. We used a combination of taxonomy, biochemistry and molecular biology to characterize the tetrasporophytes and male and female gametophytes from Chondrus individuals isolated from the rocky seashore off the northern coast of France. Transcriptomic analyses reveal differential gene expression of genes encoding several galactose-sulfurylases, carbohydrate-sulfotransferases, glycosyltransferases, and one family 16 glycoside hydrolase. Differential expression of carrageenan-related genes was found primarily between gametophytes and tetrasporophytes, but also between the male and female gametophytes. The differential expression of these multigenic genes provides a rare glimpse into cell wall biosynthesis in algae. Furthermore, it strongly supports that carrageenan metabolism holds an important role in the physiological differentiation between the isomorphic life cycle stages of Chondrus.

Expression and characterization of a κ-carrageenase from marine bacterium Wenyingzhuangia aestuarii OF219: A biotechnological tool for the depolymerization of κ-carrageenan.

κ-Carrageenases are desirable tools for tailoring the molecular weight, physicochemical properties and functionalities of κ-carrageenan, a macromolecule widely utilized in various industries. In this study, a novel GH16 family κ-carrageenase, designated as Cgk16A, was cloned from the genome of marine bacterium Wenyingzhuangia aestuarii OF219 and expressed in Escherichia coli. Its biochemical properties, kinetic parameters and hydrolytic pattern were characterized. The enzyme demonstrated a low optimal reaction temperature (25 °C) and a cold-adapted feature. As an endo-acting glycoside hydrolase, Cgk16A degraded κ-carrageenan in a random manner, and it was competent to prepare the degradation products with varying degrees of polymerization. The mass spectrometry analysis revealed that the end products of Cgk16A were majorly composed of κ-carrageenan tetrasaccharide with a minor portion of disaccharide. The enzyme showed higher enzyme-substrate affinity over all hitherto characterized GH16 κ-carrageenases, indicated by its low Km value (0.17 µM). Cgk16A could be employed as a potential biotechnological tool for depolymerizing κ-carrageenan, which would facilitate the future application of κ-carrageenan and its degradation products.