Effects of a dietary β-(1,3)(1,6)-D-glucan supplementation on intestinal microbial communities and intestinal ultrastructure of mirror carp (Cyprinus carpio L.)

AimTo assess the effects of dietary Saccharomyces cerevisiae -(1,3)(1,6)-d-glucan supplementation (MacroGard((R))) on mirror carp (Cyprinus carpio L.) intestinal microbiota and ultrastructure of the enterocyte apical brush border. Methods and ResultsCarp were fed either a control diet or diets supplemented with 01, 1 or 2% w/w MacroGard((R)). Culture-dependent microbiology revealed that aerobic heterotrophic bacterial levels were unaffected by dietary MacroGard((R)) after 2 and 4weeks. No effects were observed on the allochthonous lactic acid bacteria (LAB) populations at either time point; however, reduced autochthonous LAB populations were observed at week 4. PCR-DGGE confirmed these findings through a reduction in the abundance of autochthonous Lactococcus sp. and Vagococcus sp. in MacroGard((R))-fed fish compared with the control-fed fish. Overall, sequence analysis detected microbiota belonging to the phyla Proteobacteria, Firmicutes, Fusobacteria and unidentified uncultured bacteria. DGGE analyses also revealed that dietary MacroGard((R)) reduced the number of observed taxonomical units (OTUs) and the species richness of the allochthonous microbiota after 2weeks, but not after 4weeks. In contrast, dietary MacroGard((R)) reduced the number of OTUs, the species richness and diversity of the autochthonous microbiota after 2weeks, and those parameters remained reduced after 4weeks. Transmission electron microscopy revealed that intestinal microvilli length and density were significantly increased after 4weeks in fish fed diets supplemented with 1% MacroGard((R)). ConclusionsThis study indicates that dietary MacroGard((R)) supplementation modulates intestinal microbial communities of mirror carp and influences the morphology of the apical brush border. Significance and Impact of the StudyTo the authors' knowledge, this is the first study to investigate the effects of -(1,3)(1,6)-d-glucans on fish gut microbial communities, using culture-independent methods, and the ultrastructure of the apical brush border of the enterocytes in fish. This prebiotic-type effect may help to explain the mechanisms in which -glucans provide benefits when fed to fish.