Probiotic legacy on gut microbial assembly in fish larvae

Authors: GIATSIS, CHRISTOS - Wageningen University; RAMIRO-GARCIA, JAVIER - Wageningen University; Abernathy, Jason; VERRETH, JOHAN - Wageningen University; SMIDT, HAUKE - Wageningen University; SIPKEMA, DETMER - Wageningen University; VERDEGEM, MARC - Wageningen University

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2016
Publication Date: 9/27/2016
Citation: Giatsis, C., Ramiro-Garcia, J., Abernathy, J.W., Verreth, J., Smidt, H., Sipkema, D., Verdegem, M. 2016. Probiotic legacy on gut microbial assembly in fish larvae. Scientific Reports. 6:33965.

Interpretive Summary: Fish have many different types of bacteria in their intestines that aid in maintaining health. Probiotics are live bacteria that have a positive effect on the digestive system. This study assessed the ability of a probiotic to shape the overall bacterial community in the gut from early-life through the first month post-hatch. Nile tilapia fertilized eggs were harvested and maintained in a sanitized environment before, during, and after hatching to minimize exposure to microbes. Fish were then exposed to the probiotic and compared to fish that had not been treated with the probiotic. The overall gut bacterial populations of both control and treated fish were measured through large-scale DNA sequencing. We found that early-life probiotic exposure considerably affected gut microbial populations. Also, the probiotic appeared to have a lasting effect on fish gut microbial communities even after transfer to conventional husbandry conditions. This information will be useful in helping to determine the proper administration of probiotics in aquaculture.

Technical Abstract: Considerable efforts have been put into developing effective strategies for establishing beneficial interactions between a host and its microbiota. Early contact of fish with bacteria from their environment and its effect on early colonization in the gut has been studied in the past years. However, little is known about how the host and environment-dependent factors interact to shape gut communities, and how an early life microbial contact affects the composition of those communities. To test the effects of early microbial colonization on gut microbiota composition, axenic tilapia larvae were produced. Subsequently, these larvae were either reared under conventional conditions in active suspension tanks (AST) or first exposed to a single strain probiotic (Bacillus subtilis) for one week before switching to conventional conditions in the AST. Microbial characterization by cultivation and Illumina HiSeq sequencing of 16S rRNA gene amplicons showed that B. subtilis could be detected in gut samples during the seven days of probiotic application. Early life probiotic exposure considerably affected gut microbial composition up to the end of the experiment (day 28), regardless of the absence of B. subtilis at day 28. Change over time in gut microbiota between individuals was most pronounced in the probiotic treatment. The magnitude of change was smaller between replicated systems. Our findings indicate that early exposure to the probiotic strain impacts gut microbiota assembly, but gut microbial composition cannot yet be anticipated.