Abstract
The exposure of fish to environmental free-living microbes and its effect on early colonization in the gut have been studied in recent years. However, little is known regarding how the host and environment interact to shape gut communities during early life. Here, we tested whether the early microbial exposure of tilapia larvae affects the gut microbiota at later life stages. The experimental period was divided into three stages: axenic, probiotic and active suspension. Axenic tilapia larvae were reared either under conventional conditions (active suspension systems) or exposed to a single strain probiotic (Bacillus subtilis) added to the water. Microbial characterization by Illumina HiSeq sequencing of 16S rRNA gene amplicons showed the presence of B. subtilis in the gut during the seven days of probiotic application. Although B. subtilis was no longer detected in the guts of fish exposed to the probiotic after day 7, gut microbiota of the exposed tilapia larvae remained significantly different from that of the control treatment. Compared with the control, fish gut microbiota under probiotic treatment was less affected by spatial differences resulting from tank replication, suggesting that the early probiotic contact contributed to the subsequent observation of low inter-individual variation.
Highlights
Bacillus subtilis is a Gram- and catalase-positive, rod-shaped, facultative, anaerobic and endospore-forming bacterium observed in air, water, soil and the gastrointestinal tract of humans and animals[25,26,27,28]
Probiotic bacteria were supplied for seven consecutive days, after which the larvae from these probiotic chambers were divided over three active suspension tanks (P1-3), where these fish were further raised for another 14 days (Fig. 1)
On day 7, 120 of the axenic larvae were distributed into active suspension tanks C1, C2 and C3, whereas the remaining larvae were exposed to a high load of B. subtilis in chambers P-CH1 and P-CH2 for one week
Summary
Bacillus subtilis is a Gram- and catalase-positive, rod-shaped, facultative, anaerobic and endospore-forming bacterium observed in air, water, soil and the gastrointestinal tract of humans and animals[25,26,27,28]. (including B. subtilis) have been commonly used as probiotics in aquaculture, reflecting their antimicrobial activity against common fish and shrimp pathogens. Probiotic treatment with B. subtilis enhanced the growth and viability of beneficial lactic acid bacteria in the guts of humans and animals[39]. Prior to investigating the potential probiotic properties of B. subtilis in Nile tilapia, the scope of the present study was to assess the impact of the early microbial contact of tilapia larvae on the tilapia gut microbial assembly during later ontogenetic stages. We hypothesized that administration of the probiotic strain to fish larvae early in life, when the gut microbiota is still developing, enhances gut-colonization success and leads to the development of distinct gut communities, even after the fish are exposed to conventional husbandry conditions in active suspension systems
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