Abstract
Continuous in vitro fermentation models provide a useful tool for a fast, reproducible, and direct assessment of treatment-related changes in microbiota metabolism and composition independent of the host. In this study, we used the PolyFermS model to mimic the conditions of the chicken cecum and evaluated three nutritive media for in vitro modeling of the chicken cecal microbiota ecology and metabolism. We observed that our model inoculated with immobilized cecal microbiota and fed with a modified Viande Levure medium (mVL-3) reached a high bacterial cell density of up to approximately 10.5 log cells per mL and stable microbiota composition, akin to the host, during 82 days of continuous operation. Relevant bacterial functional groups containing primary fibrolytic (Bacteroides, Bifidobacteriaceae, Ruminococcaceae), glycolytic (Enterococcus), mucolytic (Bacteroides), proteolytic (Bacteroides), and secondary acetate-utilizing butyrate-producing and propionate-producing (Lachnospiraceae) taxa were preserved in vitro. Besides, conserved metabolic and functional Kyoto Encyclopedia of Genes and Genomes pathways were observed between in vitro microbiota and cecal inoculum microbiota as predicted by functional metagenomics analysis. Furthermore, we demonstrated that the continuous inoculation provided by the inoculum reactor generated reproducible metabolic profiles in second-stage reactors comparable to the chicken cecum, allowing for the simultaneous investigation and direct comparison of different treatments with a control. In conclusion, we showed that PolyFermS is a suitable model for mimicking chicken cecal microbiota fermentation allowing ethical and ex vivo screening of environmental factors, such as dietary additives, on chicken cecal fermentation. We report here for the first time a fermentation medium (mVL-3) that closely mimics the substrate conditions in the chicken cecum and supports the growth and metabolic activity of the cecal bacterial akin to the host. Our PolyFermS chicken cecum model is a useful tool to study microbiota functionality and structure ex vivo.
Highlights
The microbial community in the chicken gastrointestinal tract (GIT) plays an essential role in shaping health and productive performance (Oakley et al, 2014; Stanley et al, 2014)
To establish the in vitro chicken cecal microbiota model, physiological parameters such as pH, metabolites, and bacterial composition were analyzed in freshly collected ceca of Cobb-500 broiler chicken
The short-chain fatty acids (SCFAs) acetate, propionate, and butyrate and the intermediate fermentation metabolites succinate and lactate were detected in all broiler chicken ceca (Figure 2B), whereas formate was below the detection limit of the HPLC method (0.25 μmol/mL)
Summary
The microbial community in the chicken (i.e., broiler and hen) gastrointestinal tract (GIT) plays an essential role in shaping health and productive performance (Oakley et al, 2014; Stanley et al, 2014). The cecum, because of its more extensive and diverse microbial population and longer transit time of its digesta (12– 24 h), is the main region for bacterial fermentation and the main site for the colonization of pathogens (Sergeant et al, 2014; Stanley et al, 2015). The chicken cecal microbiota is dominated by the phyla Firmicutes, Bacteroidetes, and Proteobacteria (Wei et al, 2013; Rychlik, 2020) and has been implicated in nitrogen recycling by the breakdown of uric acid (Karasawa, 1999) and the supply of B vitamins and essential amino acids to the host (Sergeant et al, 2014). SCFAs contribute to the energy supply, improve mineral absorption, inhibit the growth of acid-sensitive pathogens, and have systemic health effects upon epithelial absorption (Kumar et al, 2019)
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