This paper introduces a new type of system to simulate conditions in the large intestine. This system combines removal of metabolites and water with peristaltic mixing to obtain and handle physiological concentrations of microorganisms, dry matter and microbial metabolites. The system has been designed to be complementary to the dynamic multi-compartmental system that simulates conditions in the stomach and small intestine described by Minekus et al. [Minekus M, Marteau P, Havenaar R, Huis in't Veld JHJ (1995) ATLA 23:197-209]. High densities of microorganisms, comparable to those found in the colon in vivo, were achieved by absorption of water and dialysis of metabolites through hollow-fibre membranes inside the reactor compartments. The dense chyme was mixed and transported by peristaltic movements. The potential of the system as a tool to study fermentation was demonstrated in experiments with pectin, fructo-oligosaccharide, lactulose and lactitol as substrates. Parameters such as total acid production and short-chain fatty acid (SCFA) patterns were determined with time to characterize the fermentation. The stability of the microflora in the system was tested after inoculation with fresh fecal samples and after inoculation with a microflora that was maintained in a fermenter. Both approaches resulted in total anaerobic bacterial counts higher than 10(10) colony-forming units/ml with physiological levels of Bifidobacterium, Lactobacillus, Enterobacteriaceae and Clostridium. The dry matter content was approximately 10%, while the total SCFA concentration was maintained at physiological concentrations with similar molar ratios for acetic acid, propionic acid and butyric acid as measured in vivo.
The composition of the human cecal microbiota is poorly known because of sampling difficulties. Samples of cecal fluid from eight subjects were collected via an intestinal tube. Feces were also collected. Total anaerobes, facultative anaerobes, bifidobacteria, and Bacteroides were enumerated by culture methods, and the predominant phylogenetic groups were quantified by molecular hybridization using a set of six rRNA-targeted probes. The numbers of strict anaerobes, bifidobacteria, Bacteroides, and members of the Clostridium coccoides group and Clostridium leptum subgroup were lower in the cecum. Facultative anaerobes represented 25% of total bacteria in the cecum versus 1% in the feces.
To evaluate the effect of apple components on cecal fermentations and lipid metabolism, rats were fed diets containing 5 g/100 g apple pectin (PEC), 10 g/100 g high polyphenol freeze-dried apple (PL) or both (PEC + PL). The cecal pH was slightly acidic (6.49) only in rats fed the PEC + PL diet (controls, 7.02). The cecal short-chain fatty acid pool was enlarged by all the apple fractions, with a peak of 560 micromol in rats fed the PEC + PL diet compared with 189 micromol in controls. Butyrate concentrations were 2-fold greater in rats fed the PL diet than in controls. Substantial concentrations of galacturonate and succinate (approximately 40 mmol/L) were found in the cecum of rats fed the PEC diet and, to a lesser extent, the PEC + PL diet. The PEC + PL diet significantly lowered plasma cholesterol, whereas both the PL and PEC + PL diets lowered plasma triglycerides. Liver cholesterol and triglyceride concentrations were lower in rats fed the PEC and PEC + PL diets. Fecal bile acid excretion was markedly reduced, whereas sterol excretion was significantly increased by dietary PEC. Rats fed the PEC and PEC + PL diets also had lower apparent cholesterol absorption than controls (30 compared with 43%). In conclusion, apple pectin and the polyphenol-rich fraction were more effective when fed combined together than when fed separately on large intestine fermentations and lipid metabolism, suggesting interactions between fibers and polyphenols of apple.
A new H2/CO2-utilizing acetogenic bacterium was isolated from the feces of a non-methane-excreting human subject. The two strains S5a33 and S5a36 were strictly anaerobic, gram-positive, non-sporulating coccobacilli. The isolates grew autotrophically by metabolizing H2/CO2 to form acetate as sole metabolite and were also able to grow heterotrophically on a variety of organic compounds. The major end product of glucose and fructose fermentation was acetate; the strains also formed ethanol, lactate and, to a lesser extent, isobutyrate and isovalerate. The G+C content of DNA of strain S5a33 was 45.2 mol%. 16S rRNA gene sequencing demonstrated that the two acetogenic isolates were phylogenetically identical and represent a new subline within Clostridium cluster XIVa. Based on phenotypic and phylogenetic considerations, a new species, Ruminococcus hydrogenotrophicus, is proposed. The type strain of R. hydrogenotrophicus is S5a33 (DSM 10507). Furthermore, H2/CO2 acetogenesis appeared to be a common property of most of the species phylogenetically closely related to strain S5a33 (Clostridium coccoides, Ruminococcus hansenii, and Ruminococcus productus).
1. Summary
A new species of strictly anaerobic fungus was isolated from the cow rumen. It is characterizeo by a polycentric thallus, a polynuclear rhizomycelium, mucronate zoosporangia and uniflagellated zoospores. It is also singular in that the sporocysts do not react to the specific lectins of l‐fucose, N‐acetyl‐d‐galactosamine and diacetyl chitobiose. These characteristics justify the creation of a new genus.
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