A diet rich in diatom improves the antibacterial capacity of Pacific oyster Crassostrea gigas by enhancing norepinephrine-regulated immunomodulation

Abstract

Microalgae such as dinoflagellate and diatom are the major food source of bivalve species, and sufficient food intake contributes to the immunity and the growth of bivalves. In the present study, a monoamine oxidase gene (named as CgMAO), which is the rate-limiting enzyme of norepinephrine (NE) biosynthesis, was cloned from C. gigas. After the oysters were fed with a diet rich in diatom for 21 and 40 d, the NE contents in oyster serum, as well as the mRNA expression of CgMAO in oyster haemocytes, increased significantly compared with control group. Besides, the mRNA expression of cytokines CgTNF-1 and CgIL17-5 in haemocytes and the activities of immune-related enzymes (SOD and LYZ) in oyster serum also increased significantly after diatom feeding. These results collectively suggested that sufficient microalgae intake might significantly enhance the antibacterial capacity in oyster by prompting the biosynthesis of NE and triggering the subsequent antibacterial processes modulated by NE.