Extraction of colanic acid of marine bacteria and its effects on the settlement of Mytilus coruscus plantigrades

To investigate the mechanism by which the exopolysaccharide colanic acid (CA) from marine bacteria induces the attachment of Mytilus coruscus. Juvenile M. coruscus were used as experimental subjects. The optimal culture conditions for CA production were explored, followed by extraction, purification, and monosaccharide composition analysis of CA. Different concentrations of CA were applied to induce mussel attachment, and quantitative real-time polymerase chain reaction (qRT-PCR) was performed after CA injection to evaluate the byssus attachment efficiency. In this study, a genetically engineered strain of Pseudoalteromonas marina ECSMB14103 Δ01912 with high CA production was used. Through single-factor experiments and Box-Benhnken central composite design optimization of extraction culture conditions, the optimal cultivation scheme for CA production in this strain was determined. The optimal scheme for CA production is a pH of 6.0, cultivation temperature of 30°C, cultivation time of 18 h, and inoculum of 8%. Ion chromatography analysis revealed that the product consisted of a heteropolysaccharide composed of fucosylglucose, mannose, glucose, and glucuronic acid in a molar ratio of 2∶2∶1∶1.CA concentrations of 20 μg/mL and 50 μg/mL embedded on glass slides, resulted in the highest inducing activity of M. coruscus plantigrades. Injection of purified CA into mussels showed significant up-regulation of the expression levels of Mcfp-1P, Mcfp-2 and Mcfp-5 genes, which encode adhesive proteins in byssal threads. No significant changes were observed in the expression levels of the Mcfp-1T gene after treatment with CA. Furthermore, the expression level of the Mccol2 gene significantly increased, while Mccol3 expression significantly decreased. These findings suggest that CA may regulate the settlement of M. coruscus plantigrades through promoting secretion of adhesive proteins from byssal threads, and modulating different types of collagen proteins. This study provides a theoretical basis for exploring the mechanism of inducing the settlement of M. coruscus and has potential value in applying acid-induced settlement to the aquaculture of M. coruscus.