Abstract
In this study, zebrafish were treated with Lactobacillus strains as probiotics from hatching to puberty, and the effect of treatment with L. casei BL23 on the development and immunity response of the host was investigated. Genes that were differentially expressed (DEGs) in the overall body and intestine were detected at 14 days post fertilization (dpf) and 35 dpf, respectively, using whole transcriptome sequencing (mRNAseq). We showed that zebrafish raised by continuous immersion with L. casei BL23 showed a higher final body weight at 14 dpf (P < 0.05), and 35 dpf (P < 0.01). DEGs between L. casei BL23 treatment and control group at 14 dpf were involved in myogenesis, cell adhesion, transcription regulation and DNA-binding and activator. At 35 dpf, 369 genes were DEGs in the intestine after treatment with L. casei BL23, which were involved in such categories as signaling, secretion, motor proteins, oxidoreductase and iron, tight junctions, lipid metabolism, growth regulation, proteases, and humoral and cellular effectors. KEGG analysis showed DEGs to be involved in such pathways as those associated with tight junctions and the PPAR signal pathway. RT-qPCR analysis showed that expression of insulin-like growth factors-I (igf1), peroxisome proliferator activated receptors-α (ppar-α) and -β (ppar-β), Vitamin D receptor-α (vdr-α), and retinoic acid receptor-γ (rar-γ) was up-regulated in fish treated with L. casei BL23 at 35 dpf. After 35 days of treatment, the mortality rate in L. casei BL23 treated group was lower than the control after challenge with A. hydrophila (P < 0.05), and the pro-inflammatory cytokine il-1β, anti-inflammatory cytokine il-10 and complement component 3a (c3a) showed more expression in L. casei BL23 group at 8h after challenge, 24 h after challenge, or both.. Together, these data suggest that specific Lactobacillus probiotic strains can accelerate the development profile and enhance immunity in zebrafish, which supports the rationale of early administration of probiotics in aquaculture.
Highlights
Probiotics are live microorganisms that can confer health benefits on the host when delivered in adequate amounts (FAO/WHO, 2001)
We found that the growth promoting effect of L. casei BL23 was dependent on its viability (Figure 3)
Larvae treated with live L. casei BL23 showed a higher body weight at 14 dpf and 35 dpf compared with the control (Figure 3, P < 0.05)
Summary
Probiotics are live microorganisms that can confer health benefits on the host when delivered in adequate amounts (FAO/WHO, 2001). Zebrafish have many characteristics that favor their use in host-microbe interactions research. These include the available of wealth genetic resources, the transparency during early developmental stages that permits real-time observation of host and microbial cells in vivo, and short life cycle (Lieschke and Currie, 2007). These features, combined with extensive homologies between the zebrafish and mammalian genomes, made the zebrafish a useful model for basic and biological research (Grunwald and Eisen, 2002). The zebrafish has been proven to be a practical model for studying the probiotic effects of Lactobacillus, such as lowering lipid levels (Falcinelli et al, 2015), attenuating high-fat diet-related metabolic disorders (Falcinelli et al, 2017) and anxiety-related behavior (Davis et al, 2016), promoting growth (Avella et al, 2012), and promoting disease resistance (Wang et al, 2015; He et al, 2017)
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