Lode Nollet

The effect of probiotic strains on the microbiota of the Simulator of the Human Intestinal Microbial Ecosystem (SHIME).

The aim of the present work was to study five potential probiotic strains (Lactobacillus plantarum, two strains of L. paracasei subsp. paracasei, L. rhamnosus and Bifidobacterium sp.) comparatively in the Simulator of the Human Intestinal Microbial Ecosystem (SHIME) in vitro model, and to evaluate this model as a tool in the screening and selection of probiotic bacteria. The impact of the strains on the composition of microbiota and its metabolic activities (production of lactic acid and short-chain fatty acids) was studied. Changes in composition of the microbiota become apparent as a result of probiotic treatment. A marked, but temporary, increase was noted in the number of lactic acid bacteria and bifidobacteria. The profiles of D(-) and L(+) isomers of lactic acid detected in the SHIME after addition of probiotic strains corresponded well to those that are produced in pure culture conditions. The numbers of enterobacteriaceae decreased markedly and those of clostridia detectably during the intervention, while the enterococci tended to increase after the treatment. This pattern was similar in the reactors representing both the small and large intestine in the model. The changes in short-chain fatty acids were small, and no definite trend was observed.

Influence of a synbiotic mixture consisting of Lactobacillus acidophilus 74-2 and a fructooligosaccharide preparation on the microbial ecology sustained in a simulation of the human intestinal microbial ecosystem (SHIME reactor)

Abstract Lactobacillus acidophilus 74-2, which is used in probiotic products, was administered, with fructooligosaccharide in a milk-based product, to the second vessel (duodenum/jejunum) of the SHIME reactor, an in vitro simulation of the human intestinal microbial ecology. The main focus of this study was to monitor the changes of the population density of selected bacterial species in the intestine and the changes of metabolic activities during the supplementation of L.acidophilus and fructooligosaccharide in the SHIME reactor. Interestingly, the addition of L. acidophilus 74-2 with fructooligosaccharide gave rise to an increase of bifidobacteria. Moreover, major positive changes occurred in the production of volatile fatty acids: a strong upward trend was observed especially in the case of butyric acid and propionic acid. Furthermore a noticeable increase of β-galactosidase activity was monitored, while the activity of β-glucuronidase, generally considered undesirable, declined.

The colonization of a simulator of the human intestinal microbial ecosystem by a probiotic strain fed on a fermented oat bran product: effects on the gastrointestinal microbiota.

Abstract The effects of Lactobacillus-GG-fermented oat bran product on the microbiota and its metabolic activity in the human gut were investigated, using a simulator of the human intestinal microbial ecosystem (SHIME), by analysing the bacterial population, short-chain fatty acids and gas production. In addition, the effects of fermented oat bran supernatant and supernatant samples from reactors 4, 5 and 6 (large intestine) on the growth of Escherichia coli IHE 13047, Enterococcus faecalis VTT E-93203, Lactobacillus rhamnosus VTT E-94522 (Lactobacillus GG) and Lactococcus lactis subsp. lactis VTT E-90414 were monitored to ascertain possible stimulatory/inhibitory effects by an in vitro turbidometric method. Our experiments showed that Lactobacillus GG colonized the SHIME reactor and this colonization could be maintained for several weeks without extra supplementation. Oat bran feeding also favoured the growth of bifidobacteria and caused an increase in the production of acetic, propionic and butyric acid as well as CH4 and CO2. However, the effects of oat bran, either on bacterial populations or on their metabolic activity, were not directly dose-dependent. In turbidometric measurements, the supernatant of fermented oat bran exerted an inhibitory effect of Lactobacillus GG, but stimulated the growth of enterococci.

Effect of the addition of Peptostreptococcus productus ATCC 35244 on reductive acetogenesis in the ruminal ecosystem after inhibition of methanogenesis by cell-free supernatant of Lactobacillus plantarum 80

The addition of the cell-free supernatant of Lactobacillus plantarum 80 (LP80) to ruminal samples during short-term batch experiments (24 h) led to significant increases in volatile fatty acid (VFA) production (5–30%) and to significant decreases in CH4 production (5–15%), accompanied by H2 accumulation. The supplemental addition of the reductive acetogen Peptostreptococcus productus ATCC35244 gave rise to an additional increase in VFA production, while CH4 production was decreased further (p<0.01) and H2 accumulation was abolished. The addition of P. productus without the addition of supernatant had no effect on the fermentation patterns. The utilization of H2, the lowering of the H2 recovery (2Hr) value and the high acetate production observed in the experiment indicated that both the addition of either the supernatant or the addition of the supernatant and P. productus stimulated reductive acetogenesis. The persistence of the obtained effects was further evaluated in vitro by incubation of rumen contents under pH control (6.4–6.6) during 72 h. Compared to short-term batch experiments, the stimulation of VFA production was lower (8–15%), while inhibition of CH4 production was higher (18–30%). These effects became manifest during the first 24 h of incubation and persisted during the 72 h incubation period. Infusion of both supernatant of LP80 and P. productus in the rumen of two rumen fistulated rams revealed that during the first days of administration, the addition of supernatant and P. productus decreased methanogenesis much more strongly than was observed in vitro (80%), whereas no clear effect on fermentation rate or patterns was observed. However, the effect was only transient, since at the sixth day of the administration period methanogenesis was again at the same level as during the control period. These results indicate that the supernatant of LP80 contains compounds which inhibit methanogenesis in the rumen, but that either resistance to the compound, or stimulation of rumen microbial breakdown of these compounds had occurred. Also, the ability to stimulate reductive acetogenesis by additional introduction of P. productus was only important during short-term incubations, while the effect diminished during long-term in vitro incubations or disappeared in vivo.

Effect of ammonium and nitrate application on the NO and N2O emission out of different soils.

The effect of nitrate and ammonium application (0, 50, 100 and 150 mg N kg-1 soil) was studied in an incubation experiment. Four Belgian soils, selected for different soil characteristics, were used. The application of both nitrate and ammonium caused an increase of the NO and N2O emission. The NO production from nitrate and ammonium was found to be of the same order of magnitude. At low pH the NO production was found to be highest from nitrate, at higher pH values the production was found to be higher from ammonium. This seems to be the result of the negative effect of low pH on nitrification.The ANOVA analysis was carried out to separate the effect of the form of nitrogen, quantily of N applied and soil characteristics. The total production of NO was found to depend for 97% on the soil characteristics and for 3% on the quantity of N added. The total N2O production depended for 100% on the soil characteristics.Stepwise regression analysis showed that the total NO production was best predicted by a combination of the factors CaCO3 content and NH4+ concentration in the soil. Total N2O production was best described by a combination of CaCO3, water soluble carbon (WSC) and sand-content.The N2O/NO ratio was found to be highly variable, indicating that their productions react differently to changes in conditions, or are partly independent.It may be concluded that to NO and N2O from soils both nitrification and denitrification may be equally important, their relative importance depending on local conditions such as substrate availability, water content of the soil etc. However, the NO production seems to be more nitrification dependent than the N2O production. ei]{gnE}{fnMerckx}{edSection editor}

Effect of the addition of Peptostreptococcus productus ATCC35244 on the gastro-intestinal microbiota and its activity, as simulated in an in vitro simulator of the human gastro-intestinal tract

Peptostreptococcus productus ATCC35244, a reductive acetogenic strain, was added daily over 9 successive days to the fourth vessel (ascending colon) of the SHIME, a six-stage reactor system simulating the in vivo continuous culture conditions of the human gastro-intestinal tract. Final numbers of organisms (cfu)/ml reactor contents (c) were attained such that log10 c = 6.9 ± 0.1. The addition caused the CH4 production to decrease below the detection limit while total gas and CO2 production in the fifth (transverse colon) and sixth reactor (descending colon) were lowered and the acetic acid concentration was augmented. Ending the supplementation caused CH4 production to re-establish within 4 days, while CO2 production increased much more slowly. The concentration of acetic acid only started to decrease after 7 days. The results indicate that P. productus, upon regular administration, is able to compete with methanogens for H2 in the gastro-intestinal microbial ecosystem because of its reductive acetogenic character.

Gastro-enteric methane versus sulphate and volatile fatty acid production.

The breakdown of low digestible components present in food during passage through the human and animal gastro-intestinal (GI) tract is performed by the highly diverse microbial community present in this ecosystem. Fermentation of these substances yields, besides CO2 and volatile fatty acids, H2, which is used as a substrate by three different H2-consuming bacteria. Sulphate-reducing bacteria (SRB) use H2 to reduce SOinf4sup2-to H2S, hydrogenotrophic methane-producing bacteria (MPB) use H2 to reduce CO2 to CH4 and reductive acetogens (RAC) use H2 to reduce CO2 to CH3COOH. A competition between these three bacterial groups exists for the common H2 substrate. This results generally in the dominance of one group above the other two.