The Function and the Affecting Factors of the Zebrafish Gut Microbiota

Abstract

Gut microbiota has become a topical issue in unraveling the research mechanisms underlying disease onset and progression. As an important and potential "organ," gut microbiota plays an important role in regulating intestinal epithelial cell differentiation, proliferation, metabolic function and immune response, angiogenesis and host growth. More recently, zebrafish models have been used to study the interactions between gut microbiota and hosts. It has several advantages, such as short reproductive cycle, low rearing cost, transparent larvae, high genomic similarity to humans, and easy construction of germ-free (GF) and transgenic zebrafish. In our review, we reviewed a large amount of data focusing on the close relationship between gut microbiota and host health. Moreover, we outlined the functions of gut microbiota in regulating intestinal epithelial cell differentiation, intestinal epithelial cell proliferation, metabolic function, and immune response. More, we summarized major factors that can influence the composition, abundance, and diversity of gut microbiota, which will help us to understand the significance of gut microbiota in regulating host biological functions and provide options for maintaining the balance of host health.

Keywords: factors; functions; gut microbiota; host health; zebrafish.

Figure 1

Intestinal homeostasis during the establishment of gut microbiota colonization by Myd88, toll like receptors (TLRs). Lipopolysaccharide (LPS) is required for the induction of intestinal alkaline phosphatase (IAP) activity and triggers intestinal inflammation through TLRs and Tnf signaling. IAP transcript levels were significantly elevated in the presence of gut microbiota. Exposure to exogenous LPS increases IAP transcript levels in germ-free (GF) larval zebrafish and results in higher than normal IAP levels in conventionally reared (CV) larval zebrafish. In a negative feedback loop formed by TLRs, IAP, and LPS, IAP dephosphorylates LPS, and TLRs and Tnf are reduced by LPS dephosphorylation, thereby preventing excessive intestinal inflammation.

Figure 2

Gut microbiota can induce LPS toxicity in CV zebrafish. In GF zebrafish, the gut is sterile and therefore does not induce LPS toxicity. Although gut microbiota in CV zebrafish can induce LPS toxicity, e.g., infectious shock, and even death, there is also negative feedback regulation in CV zebrafish to maintain host homeostasis.

Figure 3

Major factors affecting gut microbial composition, abundance, and diversity, excluding gender.

Figure 4

Changes in the composition of gut microbiota of zebrafish at different developmental stages. A total of three transitions of gut microbiota occurred throughout the developmental stages. The first transition of gut microbiota occurs at 10 days post-fertilization (dpf), the second transition of gut microbiota from embryo to juvenile occurs at 35–75 dpf in zebrafish, and the last transition of gut microbiota is from juvenile to early adult at 76 dpf–126 hpf. Proteobacteria and Fusobacteria are the two main core groups of zebrafish at different developmental stages, but both show different changes (increasing or decreasing) in different developmental stages.