Recombinant Saccharomyces cerevisiae Expressing P450 in Artificial Digestive Systems: a Model for Biodetoxication in the Human Digestive Environment

The use of genetically engineered microorganisms such as bacteria or yeasts as live vehicles to carry out bioconversion directly in the digestive environment is an important challenge for the development of innovative biodrugs. A system that mimics the human gastrointestinal tract was combined with a computer simulation to evaluate the survival rate and cinnamate 4-hydroxylase activity of a recombinant model of Saccharomyces cerevisiae expressing the plant P450 73A1. The yeasts showed a high level of resistance to gastric and small intestinal secretions (survival rate after 4 h of digestion, 95.6% ± 10.1% [n = 4]) but were more sensitive to the colonic conditions (survival rate after 4 h of incubation, 35.9% ± 2.7% [n = 3]). For the first time, the ability of recombinant S. cerevisiae to carry out a bioconversion reaction has been demonstrated throughout the gastrointestinal tract. In the gastric-small intestinal system, 41.0% ± 5.8% (n = 3) of the ingested trans-cinnamic acid was converted into p-coumaric acid after 4 h of digestion, as well as 8.9% ± 1.6% (n = 3) in the stomach, 13.8% ± 3.3% (n = 3) in the duodenum, 11.8% ± 3.4% (n = 3) in the jejunum, and 6.5% ± 1.0% (n = 3) in the ileum. In the large intestinal system, cinnamate 4-hydroxylase activity was detected but was too weak to be quantified. These results suggest that S. cerevisiae may afford a useful host for the development of biodrugs and may provide an innovative system for the prevention or treatment of diseases that escape classical drug action. In particular, yeasts may provide a suitable vector for biodetoxication in the digestive environment

Inulin : fermentation and microbial ecology in the intestinal tract

It is well documented that the indigenous microflora, particularly in the colon, plays an important role as a natural resistance factor against pathogenic microorganisms. The number of beneficial bacteria can be increased by specific non-digestible carbohydrates known as prebiotics. One category of prebiotic is inulin, a non-starch polysaccharide consisting of chains of fructose units coupled by β(2,1)-bonds, frequently terminated by a single glucose moiety naturally occurring as a storage carbohydrate in many plant species. From the results of various in vitro and in vivo studies in animals and humans, inulin can be considered a prebiotic with a bifidogenic factor: it selectively stimulates the in vivo growth of bacteria such as Bifidobacterium, Lactobacillus, and Bacteroides at the expense of potential pathogenic microorganisms. Regarding safety, the tolerance level for inulin is far above the bifidogenic level

A computer-controlled system to simulate conditions of the large intestine with peristaltic mixing, water absorption and absorption of fermentation products

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 1010 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