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The potential of a novel class of prebiotics, arabinoxylan oligosaccharides (AXOS), was investigated on growth performance and gut microbiota of juvenile Acipenser baerii. Two independent feeding trials of 10 or 12 weeks were performed with basal diets supplemented with 2% or 4% AXOS-32-0.30 (trial 1) and 2% AXOS-32-0.30 or AXOS-3-0.25 (trial 2), respectively. Growth performance was improved by feeding 2% AXOS-32-0.30 in both trials, although not significantly. Microbial community profiles were determined using 454-pyrosequencing with barcoded primers targeting the V3 region of the 16S rRNA gene. AXOS significantly affected the relative abundance of bacteria at the phylum, family, genus and species level. The consumption of 2% AXOS-32-0.30 increased the relative abundance of Eubacteriaceae, Clostridiaceae, Streptococcaceae and Lactobacillaceae, while the abundance of Bacillaceae was greater in response to 4% AXOS-32-0.30 and 2% AXOS-3-0.25. The abundance of Lactobacillus spp. and Lactococcus lactis was greater after 2% AXOS-32-0.30 intake. Redundancy analysis showed a distinct and significant clustering of the gut microbiota of individuals consuming an AXOS diet. In both trials, concentration of acetate, butyrate and total short-chain fatty acids (SCFAs) increased in fish fed 2% AXOS-32-0.30. Our data demonstrate a shift in the hindgut microbiome of fish consuming different preparation of AXOS, with potential application as prebiotics.

Aims: To search for nondigestible but fermentable (NDF) carbohydrates and prebiotics with a potency to promote the growth of selected bacteria in vitro. Methods and Results: The growth of three reference bacteria strains Bacillus subtilis LMG 7135 T , Carnobacterium piscicola LMG 9839, Lactobacillus plantarum LMG 9211 and one candidate probiotic bacteria Lactobacillus delbrueckii subsp. lactis was investigated over a minimum period of 48 h in the presence of b-glucan, xylo-oligosaccharide, arabinoxylo-oligosaccharide, inulin, oligofructose and glucose. Besides the capability to grow on inulin and oligofructose containing media, a distinct high growth in b-glucan based substrates and a low growth in (arabino)xylooligosaccharide containing media were evident for most bacteria tested. With the exception of B. subtilis and L. plantarum, other bacteria grew equally well or even better on different substrates than on glucose. The fermentation of studied carbohydrates by these micro-organisms was dominated by the production of acetic acid as the main short chain fatty acid. Conclusions: Selected bacteria are able to ferment and grow on NDF and prebiotic carbohydrates but in a substrate dependent manner. Significance and Impact of the Study: This study delivers a first screening of which NDF or prebiotic carbohydrates are the most promising for aquaculture feed supplementations. that are fermentable by bacteria in the human gastro-intestinal tract (Fleming et al. 1983;Stevens and Selvendran 1988). While studies of beneficial effects from prebiotics or NDFs on humans, terrestrial livestock and companion animals are numerous, only few corresponding reports on aquatic organisms in general and on fish in particular are available.The bacterial flora of fishes has been revised by Cahill (1990) and is related to their aquatic habitat. Fish have a much closer relationship with their external environment and their gut microbiota and most known fish probiotic micro-organisms belong to other genera than in terrestrial animals. Gram-negative bacteria dominate in the fish intestine but some Gram-positive ones have also been found in fish gut, including several lactic acid bacteria (LAB) (Ringø et al. 1995;Ringø and Gatesoupe 1998;Ringø and Birkbeck 1999). As an example, Carnobacterium piscicola was found dominant over a period of 18-months in the intestine of laboratory raised rainbow trout (Pond et al. 2006).Additionally, whilst the lower intestine in humans appears to be largely anaerobic and thus mainly colonized by obligate anaerobes, the fish intestine harbors aerobic or facultative anaerobic bacteria (Ringø et al. 1995;Izvekova et al. 2007). However, some studies have reported obligate anaerobes in the intestine of carp (Trust et al. 1979;Sugita et al. 1983), goldfish (Sakata et al. 1980), tilapia and gourami (Kamei et al. 1985;Sakata and Shimoeno 1989), rainbow trout (Pond et al. 2006), sturgeon (Callman andMacy 1984), Curimata pacu (Silva et al. 2005), dragonets, Japanese whiting, rudder fish and bambooleaf wrasse (...

To select and characterize potential probiotic bacteria from the gut microbiota of Siberian sturgeon (Acipenser baerii), 129 strains isolated from the hindgut were screened for antagonistic activity against five fish pathogens. Ten isolates showed antagonism towards three or more pathogens. Nine of these isolates were Gram-positive, belonging to Lactococcus (seven) and Bacillus (two), and a single strain belonging to the Gram-negative Citrobacter. These inhibitory isolates were identified using genetic, phentotypic and biochemical traits, and further characterized by in vitro tests assessing the adhesion and growth in mucus and resistance to gastric and intestinal fluids. The candidate probiotics were determined to be non-pathogenic through an in vivo study. Based on these assays, Lactococcus lactis ssp. lactis STG45 and STG81 showed the broadest inhibitory potential, a high viability in simulated gastrointestinal juice and the highest adhesion capacity to mucus. They were therefore selected as the most promising candidate probiotics. This is the first study screening probiotics among the gut microflora of Siberian sturgeon.