Improvements of immune genes and intestinal microbiota composition of turbot (Scophthalmus maximus) with dietary oregano oil and probiotics

Abstract

Plant extract (oregano oil) and probiotics as dietary additives can improve weight gain, feed efficiency and disease resistance in cultured fish. In this research, we evaluated the effects of oregano oil and probiotics (strain Bacillus coagulans G1902) on growth performance, intestinal microbiota and expression of intestinal and splenic immune related genes (IL-1β, TNF-α, MHC-I and IFIH1) of turbots (Scophthalmus maximus) by a 30-day feeding experiment. Three treatment groups including oregano oil supplementation (O) group, probiotic strain B. coagulans supplementation (P) group and common feeding (CK) group were designed, respectively. As a result, turbots showed better growth performance, increased digestion and absorption capacity, and decreased incidence rates of A. salmonicida infection in O and P groups compared with CK group. The expression levels of IL-1β, TNF-α, MHC-I and IFIH1 were significantly up-regulated in O group after 10 days of oregano oil feeding (P < 0.05). We performed 16S rRNA sequencing analysis, identified the differentially abundant taxa, predicted metabolic pathways of intestinal microbiota and constructed the co-abundance networks. The supplementary of oregano oil or probiotics decreased the relative abundances of Listonella and Sphingomonas and increased the relative abundances of several potential beneficial bacteria (such as Akkermansia, Bifidobacteium and Faecalibacterium) (LDA > 2, P < 0.05). The relative abundance of bacterial secretion system decreased in turbots supplemented dietary oregano oil on day 20 and 30, and several pathways related to glycan, lipid and amino acid metabolism upregulated in turbots supplemented dietary probiotics on day 30 (P < 0.05). Oregano oil or B. coagulans may provide health benefits by modulate gut microbiota and impact the immunostimulatory effects of the host. Our findings provide a new perspective to explore the mechanism of growth improvement and immune enhancement by usage of oregano oil or probiotics, and study the application of oregano oil and probiotics as fish feeds in health culture of turbots.