The Change of Teleost Skin Commensal Microbiota Is Associated With Skin Mucosal Transcriptomic Responses During Parasitic Infection by Ichthyophthirius multifillis.

Xiaoting Zhang,Yaxing Yin,Weiguang Kong,Zhen Xu,Xuezhen Zhang,Liguo Ding,Zhenyu Huang,Yongyao Yu

doi:10.3389/fimmu.2018.02972

Abstract

Teleost skin serves as the first line of defense against invading pathogens, and contain a skin-associated lymphoid tissue (SALT) that elicit gut-like immune responses against antigen stimulation. Moreover, exposed to the water environment and the pathogens therein, teleost skin is also known to be colonized by diverse microbial communities. However, little is known about the interactions between microbiota and the teleost skin mucosal immune system, especially dynamic changes about the interactions under pathogen infection. We hypothesized that dramatic changes of microbial communities and strong mucosal immune response would be present in the skin of aquatic vertebrate under parasite infection. To confirm this hypothesis, we construct an infected model with rainbow trout (Oncorhynchus mykiss), which was experimentally challenged by Ichthyophthirius multifiliis (Ich). H & E staining of trout skin indicates the successful invasion of Ich and shows the morphological changes caused by Ich infection. Critically, increased mRNA expression levels of immune-related genes were detected in trout skin from experimental groups using qRT-PCR, which were further studied by RNA-Seq analysis. Here, through transcriptomics, we detected that complement factors, pro-inflammatory cytokines, and antimicrobial genes were strikingly induced in the skin of infected fish. Moreover, high alpha diversity values of microbiota in trout skin from the experimental groups were discovered. Interestingly, we found that Ich infection led to a decreased abundance of skin commensals and increased colonization of opportunistic bacteria through 16S rRNA pyrosequencing, which were mainly characterized by lose of Proteobacteria and increased intensity of Flavobacteriaceae. To our knowledge, our results suggest for the first time that parasitic infection could inhibit symbionts and offer opportunities for other pathogens' secondary infection in teleost skin.

Highlights

The skin of vertebrates serve as the first line of defense against pathogens’ invading and harbor millions of microorganisms that form a very ancient and successful symbiosis between prokaryotes and metazoans
We calculated the differences in the microbial diversity and community in trout skin between the experimental and control groups by using the operational taxonomic units (OTUs) noted above for further analysis with UniFrac
High alpha diversity values of microbiota in trout skin from the experimental groups were discovered at both 24 h (Student’s t-test, P = 0.0407 for observed species and P = 0.0031 for Shannon index) and 7 d (P = 0.0074 for observed species and P = 0.0375 for Shannon index) after Ichthyophthirius multifiliis (Ich) infection when compared with the control group (Figure 5A, Table 3)

Summary

Introduction

The skin of vertebrates serve as the first line of defense against pathogens’ invading and harbor millions of microorganisms that form a very ancient and successful symbiosis between prokaryotes and metazoans. In contrast to mammalian skin, teleost skin has been considered as mucosal surface that harbors abundant mucus-producing cells, lacks keratinization, and possesses living epithelial cells that make direct contact with the water medium [1, 2]. Teleost skin is known to be colonized by diverse microbial communities [4]. The presence of bacterial communities in teleost skin suggests a tight cross-talk between the microbiota and mucosal immune system. Many studies have revealed the interaction between microbial communities and the host mucosal immune system of teleost fish [5,6,7,8,9], information regarding that in the skin remains limited [10]

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Results

Conclusion