Biomedical subjects

I De Smet

Publications and source records attributed to I De Smet.

7 recordsLinked to original sources

PubMed2004

An easy and versatile embedding method for transverse sections.

In several research areas, transverse sections are indispensable for studying structural aspects of specimens. However, the oriented embedding of small cylindrical samples can become problematic, especially when transverse sections at right angles to the main axis of the object are desired. Here, we describe an easy and low-cost technique for oriented embedding of small (psi < 500 micro m) as well as of larger specimens (psi > 500 micro m). The usefulness of the technique is demonstrated for roots and stamens of Arabidopsis thaliana and for adventitious roots of Asplenium demerkense, as examples of small and larger cylindrical samples, respectively. Furthermore, several types of resin (glycol methacrylate, epoxy and acrylic resins) were successfully tested, showing the applicability of the technique for light and electron microscopy and for immunolocalizations. In conclusion, the principle of the technique can be extended to several resins and a wide variety of specimen types, such as stems, leaves and textile fibres. The originality of the technique lies in its simplicity combined with its high efficiency to produce well-oriented transverse sections.

Arabidopsis↗

PubMed2003

Microbial reduction and precipitation of vanadium by Shewanella oneidensis.

Shewanella oneidensis couples anaerobic oxidation of lactate, formate, and pyruvate to the reduction of vanadium pentoxide (V(V)). The bacterium reduces V(V) (vanadate ion) to V(IV) (vanadyl ion) in an anaerobic atmosphere. The resulting vanadyl ion precipitates as a V(IV)-containing solid.

Anaerobiosis↗

PubMed2001

ABA plays a central role in mediating the regulatory effects of nitrate on root branching in Arabidopsis.

The formation of lateral roots (LR) is a major post-embryonic developmental event in plants. In Arabidopsis thaliana, LR development is inhibited by high concentrations of NO3(-). Here we present strong evidence that ABA plays an important role in mediating the effects of NO3(-) on LR formation. Firstly, the inhibitory effect of NO3(-) is significantly reduced in three ABA insensitive mutants, abi4-1, abi4-2 and abi5-1, but not in abi1-1, abi2-1 and abi3-1. Secondly, inhibition by NO3(-) is significantly reduced, but not completely abolished, in four ABA synthesis mutants, aba1-1, aba2-3, aba2-4 and aba3-2. These results indicate that there are two regulatory pathways mediating the inhibitory effects of NO3(-) in A. thaliana roots. One pathway is ABA-dependent and involves ABI4 and ABI5, whereas the second pathway is ABA-independent. In addition, ABA also plays a role in mediating the stimulation of LR elongation by local NO3(-) applications.

Abscisic Acid↗

PubMed1999

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.

Bifidobacterium↗

PubMed1998

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.

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, shortchain 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.

Avena↗

PubMed1998

Cholesterol lowering in pigs through enhanced bacterial bile salt hydrolase activity.

The effect of feeding live Lactobacillus reuteri cells containing active bile salt hydrolase (BSH) on plasma cholesterol levels was studied in pigs. During an experiment lasting 13 weeks, twenty pigs were fed on a high-fat, high-cholesterol, low-fibre for the first 10 weeks, and a regular pig diet for the last 3 weeks. One group of animals received, twice daily, 11.25 (SD 0.16) log10 colony forming units of the potential probiotic bacteria for 4 weeks (from week 3 until week 7). From week 8 onwards, the treated group was again fed on the same diet as the control group without additions. The total faecal Lactobacillus counts were only significantly higher in the treated pigs during the first 2 weeks of L reuteri feeding. Based on limited data, it was suggested that the administered Lactobacillus species had caused a temporary shift within the indigenous Lactobacillus population rather than permanently colonizing the intestinal tract. The probiotic feeding brought about significant lowering (P < or = 0.05) of total and LDL-cholesterol concentrations in the treated pigs compared with the control pigs, while no change in HDL-cholesterol concentration was observed. The data for faecal output of neutral sterols and bile salts were highly variable between the animals of each group, yet they indicated an increased output in the treated pigs. Although the blood cholesterol levels went up in both groups during the 3 weeks following the Lactobacillus administration period, significantly lower serum total and LDL-cholesterol levels were observed in the treated pigs. During the final 3 weeks of normalization to the regular diet, cholesterol concentrations significantly decreased in both animal groups and the differences in total and LDL-cholesterol concentrations between the groups largely disappeared.

Amidohydrolases↗

PubMed1995

Significance of bile salt hydrolytic activities of lactobacilli.

Bile salt hydrolase (BSH) activity was shown to be constitutive and substrate-specific: the BSH isogenic Lactobacillus plantarum wild type (LP80 WT) and BSH overproducing LP80 (pCBH1) strains preferentially hydrolysed glycodeoxycholic acid (GDCA), whereas the hamster Lact. animalis isolates H362 and H364 showed a higher affinity for taurodeoxycholic acid (TDCA). In viability studies in the presence of nutrients, it was demonstrated that GDCA exerted a higher toxicity than TDCA in a pH-dependent manner. This toxicity was inversely proportionate to the BSH activity level of the strains tested, indicating that BSH activity contributed towards bile salt resistance when appropriate nutrients were available. The high toxicity of GDCA relative to TDCA was suggested to be caused by their weak and strong acid properties respectively. It was therefore hypothesized that the protonated form of bile salts exhibited toxicity as it imported protons in the cell. This puts an energy-burden on BSH- lactobacilli which undergo intracellular acidification. BSH+ cells primarily protect themselves through the formation of the weaker DCA compound, which can help negate the pH-drop by recapturing and exporting the co-transported proton. However, since DCA is more toxic than its conjugated counterparts, an additional energy-dependent detoxification of DCA is suggested.

Animals↗