Intestinal morphology, immunity and microbiota response to dietary fibers in largemouth bass, Micropterus salmoide.

This study is aimed at identifying the effects of dietary fiber on gut health, as well as the association between that understanding and fiber consumption in fish. A total of 300 juvenile largemouth bass (micropterus salmoides, initial average weight: 15.38 ± 0.16g) were randomly divided into three treatment groups (4 replicates per group). Fish were fed with isoproteic and isolipidic diets containing 0% (low fiber, LF), 4% (moderate fiber, MF) and 8% (high fiber, HF) soybean fiber, respectively. The intestine and intestinal content of test fish per treatment group after 56 days of treatment were sampled. The results showed that the anterior intestinal sections had normal histological architecture, and no considerable damage or inflammation was observed in any histological section from all subjects examined. Curiously, fish fed the MF diet had better histological alterations than the other treatments. Meanwhile, the intestinal antioxidant capacity in the MF group was significantly promoted when compared to the other groups, as well as up-regulated expression of antioxidant-related genes including sod, cat and gpx with increasing dietary fiber concentrations. Importantly, the administrations of MF diet remarkably elevated largemouth bass innate immune parameters include intestinal inducible nitric oxide synthase (iNOS) activity, nitric oxide (NO) and total protein content. Similarly, dietary administrations of fiber down-regulated notablely the expression of pro-inflammatory cytokines including IL-8, IL-1ß and TNFα, whereas up-regulated tolerogenic cytokine IL-10 and TGF-ß1 mRNA levels. In addition, dietary fibers also modulated the community structure of the intestinal microbiota by significantly altering bacterial diversity. Dietary supplemental fibers regulated intestinal microbiota in largemouth bass, characterized by a reduced abundance of Fusobacteria along with increased abundances of Proteobacteria and Firmicutes. Taken together, the present results suggested that moderate fiber supplementation was beneficial to promoting intestinal health status of fish through antioxidant and anti-inflammatory effects, which could be at least partially responsible by the modulation of gut microbial composition.

Characterization of Trichococcus paludicola sp. nov. and Trichococcus alkaliphilus sp. nov., isolated from a high-elevation wetland, by phenotypic and genomic analyses.

Two psychrotolerant facultative anaerobes, strains B7-2T and B5T, were isolated from the Zoige Wetland on the Qinghai-Tibetan Plateau. The 16S rRNA gene sequences of strains B7-2T and B5T shared high similarity (>99 %) with those of the type strains of the genus Trichococcus, while their digital DNA-DNA hybridization values with each other (49 %) and with the reference type strains (48-23 %) were lower than 70 %, which suggest that they represent two novel species of the genus Trichococcus. Cells of strains B7-2T and B5T were immotile cocci, grew in the temperature range of 4-37 °C (optimum 25 °C) and were alkaliphilic with optimum growth at pH 9.0. The major components of the cellular fatty acids were C16 : 0, anteiso-C17 : 0 and C18 : 0 for strain B7-2T, and C16 : 0, anteiso-C17 : 0, C18 : 1ω9c and C18 : 0 for strain B5T. The genomic DNA G+C contents were 46.0 and 46.7 mol% for strains B7-2T and B5T, respectively. Based on physiological and genomic characteristics, it is suggested that strains B7-2T and B5T represent two novel species within the genus Trichococcus, for which the names Trichococcus paludicola sp. nov. and Trichococcus alkaliphilus sp. nov. are proposed. The type strains are B7-2T (=DSM 104691T=KCTC 33886T) and B5T (=DSM 104692T=KCTC 33885T), respectively.