BackgroundProkaryotic 16S ribosomal RNA (rRNA) sequences are widely used in environmental microbiology and molecular evolution as reliable markers for the taxonomic classification and phylogenetic analysis of microbes. Restricted by current sequencing techniques, the massive sequencing of 16S rRNA gene amplicons encompassing the full length of genes is not yet feasible. Thus, the selection of the most efficient hypervariable regions for phylogenetic analysis and taxonomic classification is still debated. In the present study, several bioinformatics tools were integrated to build an in silico pipeline to evaluate the phylogenetic sensitivity of the hypervariable regions compared with the corresponding full-length sequences.ResultsThe correlation of seven sub-regions was inferred from the geodesic distance, a parameter that is applied to quantitatively compare the topology of different phylogenetic trees constructed using the sequences from different sub-regions. The relationship between different sub-regions based on the geodesic distance indicated that V4-V6 were the most reliable regions for representing the full-length 16S rRNA sequences in the phylogenetic analysis of most bacterial phyla, while V2 and V8 were the least reliable regions.ConclusionsOur results suggest that V4-V6 might be optimal sub-regions for the design of universal primers with superior phylogenetic resolution for bacterial phyla. A potential relationship between function and the evolution of 16S rRNA is also discussed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12859-016-0992-y) contains supplementary material, which is available to authorized users.
Dietary supplementation with conjugated
linoleic acid (CLA) has been
reported
to alleviate
the effect of colitis in mice, but the mechanisms involved need further
exploration. The study aimed to investigate how orally administered
CLA alleviates dextran sulfate sodium (DSS)-induced colitis in mice.
CLA was administered in five different doses: 40, 20, 10, 5, and 2.5
mg/day. Doses of CLA at 10 mg/day and higher alleviated colitis symptoms
and reduced inflammation induced by DSS, in which 40, 20, and 10 mg/day
CLA significantly increased the concentration of mucin2 and goblet
cells, but neither 5 mg/day CLA nor 2.5 mg/day CLA had any effects.
Meanwhile, 40 and 20 mg/day CLA treatments significantly upregulated
the concentration of tight junction proteins (ZO-1, occludin, and
claudin-3) and ameliorated epithelial apoptosis caused by DSS. Moreover,
oxidative-stress-related enzymes (superoxide dismutase, glutathione
peroxidase, and catalase) and inflammatory cytokines [tumor necrosis
factor-α, interleukin (IL)-10, and IL-6] were modulated by 40
and 20 mg/day CLA. Furthermore, 40 mg/day CLA rebalanced the gut microbiota
damaged by DSS, including reducing Bacteroides and
increasing Bifidobacterium and Odoribacter. In conclusion, CLA supplementation alleviated DSS-induced colitis
in a dose-dependent manner by modulating inflammatory cytokines and
oxidation stress, maintaining the mucosal barrier, and reverting microbiota
changes.
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