Chemotaxis toward carbohydrates and peptides by mixed ruminal protozoa when fed, fasted, or incubated with polyunsaturated fatty acids.

In contrast to the well-characterized chemotaxis and migratory behavior between the dorsal and ventral locations of the rumen by isotrichids, we hypothesized that chemotaxis toward soluble nutrients maintains entodiniomorphid protozoa in the particulate fraction. The objectives of these experiments were to compare the dose-responsive chemotaxis (1) toward different glucose concentrations when ruminal samples were harvested from fed versus fasted cows; (2) toward increasing concentrations of glucose compared with xylose when protozoa were harvested from a fed cow; (3) toward peptides of bacterial, protozoal, and soy origin; and (4) toward glucose when mixed ruminal protozoa were previously incubated for 0, 3, or 6h in the presence of emulsified polyunsaturated fatty acids (PUFA; Liposyn II, Hospira, Lake Forest, IL). In experiment 1, isotrichid protozoa decreased chemotaxis toward increasing glucose concentration when cows were fasted. Entodiniomorphids exhibited chemotaxis to similar concentrations of glucose as did isotrichids, but to a lesser magnitude of response. In experiment 2, xylose was chemotactic to both groups. Xylose might draw fibrolytic entodiniomorphid protozoa toward newly ingested feed. In contrast, even though isotrichids should not use xylose as an energy source, they were highly chemoattracted to xylose. In experiment 3, entodiniomorphids were not selectively chemoattracted toward bacterial or protozoal peptides compared with soy peptides. In experiment 4, despite isotrichid populations decreasing in abundance with increasing time of incubation in PUFA, chemotaxis to glucose remained unchanged. In contrast, entodiniomorphids recovered chemotaxis to glucose with increased time of PUFA incubation. Current results support isotrichid chemotaxis to sugars but also our hypothesis that a more moderate chemotaxis toward glucose and peptides explains how they swim in the fluid but pass from the rumen with the potentially digestible fraction of particulates.

Utilización de Candida guilliermondii aislada del corozo chiquito (Bactris guineensis) en la producción de xilitol / Utilization of Candida guilliermondii isolated of corozo chiquito (Bactris guineensis) in the production of xylitol

La levadura Candida guilliermondii es objeto de estudio debido a su capacidad de producir xilitol aprovechando compuestos hemicelulósicos ricos en xilosa, dado esto, la cepa Candida guilliermondii aislada del fruto del corozo chiquito (Bactris guineensis) fue usada en este estudio con el fin de evaluar su capacidad para producir xilitol sobre un sustrato hidrolizado de cascarilla de arroz. El objetivo de este trabajo fue determinar los parámetros fermentativos como producción de xilitol, productividad volumétrica (Qp) y rendimiento de sustrato en producto (Yp/s) durante la fermentación con la cepa nativa Candida guilliermondii. Se emplearon 200 ml de medio de cultivo hidrolizado de cascarilla de arroz, el cual contenía una concentración de xilosa de 27,5 g/L. La fermentación se llevó a cabo bajo las siguientes condiciones: temperatura 30 ºC, pH del medio 5,8, agitación 120 rpm e inóculo adaptado de 3 g/L. Los resultados mostraron que después de 120 horas de fermentación se obtuvieron 2,6 g/L de xilitol con productividad volumétrica (Qp) de 0,02 g/L-h y rendimiento de sustrato en producto (Yp/s) de 0,13 g/g. De esta manera, la cepa nativa Candida guilliermondii, aislada del fruto de Corozo chiquito (Bactris guineensis), produjo xilitol bajo condiciones específicas de fermentación.

The yeast Candida guilliermondii has been studied due to its ability to produce xylitol in xylose-rich hemicellulosic compounds, Candida guilliermondii strain isolated from the fruit of Corozo chiquito (Bactris guineensis) was used in this study to assess their ability to xylitol production on these substrates. The aim of this study was to determine the fermentation parameters such as xylitol production, volumetric productivity (Qp) and yield of xylitol production (Yp/s) during fermentation with the native strain Candida guilliermondii. Was used 200 ml of culture medium rice husk hydrolysate, which contained a xylose concentration of 27.5 g/L. The fermentation was carried out under the following conditions: temperature 30 ºC, pH of 5.8, agitation 120 rpm and adapted inoculum of 3 g/L. The results showed that after 120 hours of fermentation 2.6 g / L of xylitol was achieved with volumetric productivity (Qp) 0.02 g/L-h and 0.13 g/g yield of xylitol production (Yp/s). The native strain Candida guilliermondii, isolated from the fruit of Corozo chiquito (Bactris guineensis) produced xylitol fermentation under specific conditions.

D-Xylose absorption capacity of broiler intestine in response to phytic acid.

1. Dietary phytic acid (PA) reduces the apparent digestion and of dietary nutrients, increases the excretion of endogenous amino acids and minerals and reduces the concentration of blood glucose. 2. An experiment was conducted to examine the effect of phytic acid on the absorption capacity of the intestine in broiler chicken, using a D-xylose absorption test. 3. Three groups of ten 26-d-old apparently healthy broiler cockerels (Ross 308) were dosed with D-xylose solution (500 mg/kg BW, Group 1) or D-xylose solution + PA (330 or 660 mg/5 ml/bird, in groups 2 and 3), respectively. The plasma concentration of D-xylose was measured at 40-min intervals after ingestion of test materials, for a total of 160 min. 4. There was a quadratic correlation between the concentration of plasma D-xylose and time in all experimental groups (P < 0001, R(2)= 078, 080 and 081 for groups 1-3, respectively). Ingestion of PA at 660 mg reduced the concentration of plasma D-xylose by 216 and 105% at 40 and 80 min after ingestion of the test material, indicating a lower absorption of this sugar. 5. It was concluded that dietary phytates might affect the productive performance of chicken, at least partly, by disturbing the transport mechanisms involved in the absorption of nutrients.

A xylose-inducible expression system for Lactococcus lactis.

A new controlled production system to target heterologous proteins to cytoplasm or extracellular medium is described for Lactococcus lactis NCDO2118. It is based on the use of a xylose-inducible lactococcal promoter, P(xylT). The capacities of this system to produce cytoplasmic and secreted proteins were tested using the Staphylococcus aureus nuclease gene (nuc) fused or not to the lactococcal Usp45 signal peptide. Xylose-inducible nuc expression is tightly controlled and resulted in high-level and long-term protein production, and correct targeting either to the cytoplasm or to the extracellular medium. Furthermore, this expression system is versatile and can be switched on or off easily by adding either xylose or glucose, respectively. These results confirm the potential of this expression system as an alternative and useful tool for the production of proteins of interest in L. lactis.

Xylose as a nectar sugar: from biochemistry to ecology.

Studies of nectar sugar composition in the Proteaceae, an ancient southern hemisphere plant family, have demonstrated that xylose comprises up to 39% of nectar sugar in two genera, Protea and Faurea, and may therefore represent a substantial fraction of the energy available to pollinators of these plants. Although insect and bird pollinators of Protea species are averse to xylose, mice (Aethomys namaquensis) will drink pure xylose, which is metabolized either by gut bacteria or by the mouse tissues. In the form of xylan polymers, the pentose sugar D-xylose is a structural component of plant cell walls, and there is considerable biotechnological interest in xylose fermentation. Bacteria and yeasts convert D-xylose to D-xylulose and thence via the pentose phosphate pathway to fructose-6-phosphate, which is either oxidized or fermented to ethanol. Gut symbionts of rodent pollinators may be analogous to ruminal xylose-metabolizing bacteria. The presence of xylose in Protea and Faurea nectar remains puzzling in view of pollinator aversions: even for rodent pollinators, it is the least preferred nectar sugar. In the generalized pollination systems of the Proteaceae, a coevolutionary explanation for nectar xylose as an attractant for mammalian pollinators is probably less likely than one involving plant physiology, with xylose in phloem sap being secreted passively into the nectar.

[Effect of casein derived peptides on D-xylose absorption and small intestinal motility in dogs]. / Efecto de fracciones pépticas derivadas de la caseína en la absorción de D-xilosa y motilidad intestinal en el perro. Estudio preliminar.

BACKGROUND: The presence of food in the intestinal lumen increases absorption from an isolated intestinal loop, the mechanisms involved are unknown. Casein, and its respective hydrolysate, increased D-xylose absorption in both normal volunteers and experimental animals; this effect was associated with prolonged small intestinal transit time and a decrease of motor activity. AIMS: To separate from casein hydrolysate, groups of peptides and to investigate their effects on both D-xylose absorption and small intestinal motility. MATERIAL AND METHODS: Studies were performed on five dogs with a surgically implanted duodenal cannula. Three groups of peptides were separated by means of a Silica Gel 60 column and were continuously infused through the duodenal cannula. After 15 min, 5 g of D-xylose were injected in the duodenum, plasma levels were measured, and the area under the curve was estimated. Motility was recorded by means of infused catheters and external transducers. RESULTS: Plasma levels of D-xylose were significantly increased during the infusion of one group of peptides compared to the others. In addition, the area under the curve: 3366 +/- 885 mg x min-1 observed with this group was significantly greater than the other two groups: 1432 +/- 183 mg x min-1 and 1137 +/- 280 mg x min-1 respectively. No statistically significant differences in motor activity were observed between the different groups of peptides. CONCLUSIONS: A group of peptides derived from casein was characterized by increasing D-xylose absorption. The presence of beta casomorphines might be the possible mechanism involved.

Pharmacokinetics and absolute bioavailability of oral foscarnet in human immunodeficiency virus-seropositive patients.

The pharmacokinetics, absolute bioavailability, accumulation, and tolerability over 8 days of an oral formulation of foscarnet (90 mg/kg of body weight once daily [QD] [n = 6], 90 mg/kg twice daily [BID] [n = 6], and 180 mg/kg QD [n = 31) were investigated in 15 asymptomatic, human immunodeficiency virus-seropositive male patients free of active cytomegalovirus infection and with normal upper gastrointestinal function. Peak plasma drug concentrations were (mean +/- standard deviation) 46.4 +/- 10.8 microM (90 mg/kg QD), 45.7 +/- 6.9 microM (90 mg/ kg BID), and 64.9 +/- 31.7 microM (180 mg/kg QD) on day 1 and rose to 86.2 +/- 35.8, 78.7 +/- 35.2, and 86.4 +/- 25.0 microM, respectively, on day 8. The mean peak concentration in plasma following the intravenous administration of foscarnet (90 mg/kg) was 887.3 +/- 102.7 microM (n = 13). The terminal half-life in plasma remained unchanged, averaging 5.5 +/- 2.2 h on day 1 (n = 15) and 6.6 +/- 1.9 h on day 8 (n = 13), whereas it was 5.7 +/- 0.7 h following intravenous dosing. Oral bioavailabilities were 9.1% +/- 2.2% (90 mg/kg QD), 9.5% +/- 1.7% (90 mg/kg BID), and 7.6% +/- 3.7% (180 mg/kg QD); the accumulation ratios on the 8th day of dosing were 2.1 +/- 1.1, 1.8 +/- 0.4, and 1.7 +/- 0.7, respectively. The overall 24-h urinary excretion of oral foscarnet averaged 7.8% +/- 2.6% (day 1) and 13.4% +/- 6.0% (day 8), whereas it was 95.0% +/- 4.9% after intravenous dosing. The glomerular filtration rate and creatinine clearance remained constant, and the mean 24-h renal clearances of foscarnet for the entire study group were 96 +/- 18 ml/min (day 1), 88 +/- 13 ml/min (day 8), and 103 +/- 16 ml/min after intravenous dosing. Adverse effects were largely confined to gastrointestinal disturbances, with all subjects experiencing diarrhea that was dose dependent in its severity. The results suggest that the formulation studied would require significant improvement with respect to tolerability and bioavailability to gain clinical acceptance.

The effect of amino acids on the intestinal transport of L- and D-xylose in vitro.

1. The intestinal transport of D-xylose by sacs of everted small intestine of the hamster is partially inhibited by L-histidine in concentrations of 5, 10 and 20 mM but not of 2 mM.2. 20 mM concentrations of D-histidine and L-methionine also produce inhibition.3. The inhibition is not due to an alteration in water transport or to a change in pH of the incubating medium.4. The rate of the intestinal transport of L-xylose is about (1/4) of the rate of D-xylose transport and is unaffected by a 20 mM concentration of L-histidine.