ß-1,3 glucan derived from Euglena gracilis and Algamune™ enhances innate immune responses of red drum (Sciaenops ocellatus L.)

Authors: YAMAMOTO, FERNANDO - Texas A&M University; YIN, FEI - Ningbo University; ROSSI JR, WALDEMAR - Texas A&M University; Hume, Michael; GATLIN III, DELBERT - Texas A&M University

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2018
Publication Date: 6/1/2018
Citation: Yamamoto, F.Y., Yin, F., Rossi Jr, W., Hume, M.E., Gatlin III, D.M. 2018. ß-1,3 glucan derived from Euglena gracilis and Algamune™ enhances innate immune responses of red drum (Sciaenops ocellatus L.). Fish and Shellfish Immunology. 77:273-279. https://doi.org/10.1016/j.fsi.2018.04.003.
DOI: https://doi.org/10.1016/j.fsi.2018.04.003

Interpretive Summary: The complex sugars ß-glucan improve immune responses to bacterial infection in fish. A commercial form of ß-glucan, Algamune, is prepared from dried, one-celled algae. This study assessed immune responses in red drum fish fed Algamune in the diet. Isolated red drum white blood cells were incubated with increasing amounts of Algamune as well as purified ß-glucan as a control treatment. Increased anti-bacterial activity against a Streptococcus and production of a protective form of oxygen were stimulated by Algamune as well as by the purified ß-glucan. Next, a study was conducted using red drum fish and different experimental groups given increasing amounts of Algamune in the feed. No significant differences were detected regarding growth of the fish over the 21 days of the study. At 21 days, intestinal bacteria were found, using a molecular technique, to be the same for all levels of Algamune in the feed. No differences were detected for the levels of protective oxygen molecules in the blood. However, greater bacteria killing activity in the blood was seen at the higher levels of Algamune in feed compared to feed containing no Algamune. Results indicate that Algamune from the one-cell algae stimulated increased immune system activity in red drum fish. These results are of interest to aquaculture producers and researchers seeking to reduce stress response and enhance protection against bacterial infection in aquaculture-reared fish.

Technical Abstract: To reduce susceptibility to stressors and diseases, immune-modulators such as ß-glucans have been proven effective tools to enhance the innate immune responses of fish. Consequently, commercial sources of this polysaccharide are becoming increasingly more available. AlgamuneTM is a commercial additive produced from Euglena gracilis as a source of ß-1,3-glucan. In order to evaluate the immunomodulatory effects of this ß-glucan product, the present study assessed the innate immune parameters of red drum (Sciaenops ocellatus) exposed to AlgamuneTM ex vivo and in vivo. Isolated kidney phagocytes were incubated with graded concentrations (0, 0.2, 0.4, 0.8, 1.6, and 3.2 mg L-1) of dried Euglena gracilis (AlgamuneTM) as well as purified Paramylon (linear ß-1,3 glucan). Increased bactericidal activity against Streptococcus iniae, and production of intracellular O2- anion superoxide were stimulated by both ß-glucan sources. A reduced activity of extracellular anion superoxide was observed by the phagocytes incubated with AlgamuneTM. After corroborating the effectiveness of the glucan source ex vivo, a feeding trial was conducted using red drum juveniles (~26.6 g initial weight). Fish were fed diets with graded levels of AlgamuneTM (0, 100, 200, 400, and 800 mg kg-1) twice daily for 21 days. No significant differences were detected regarding production performance parameters. At the end of the feeding trial, blood, intestinal content, and kidney were sampled. Intestinal microbiota from fecal material was analyzed through denaturing gradient gel electrophoresis (DGGE) and was found to be similar among all treatments. No significant differences were detected for oxidative radical production from whole blood, isolated phagocytes, and plasma lysozyme activity. However, the total hemolytic activity of red drum plasma was increased in fish fed 100 and 200 mg kg-1 of dietary AlgamuneTM when compared to fish fed the basal diet. Based on results from both ex vivo and in vivo trials, ß-glucan from AlgamuneTM was demonstrated to have immunostimulatory effects on red drum.