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Biomedical subjects

J Simůnek

Publications and source records attributed to J Simůnek.

At least 19 recordsLinked to original sources
PubMed2006

Operator-splitting errors in coupled reactive transport codes for transient variably saturated flow and contaminant transport in layered soil profiles.

One possible way of integrating subsurface flow and transport processes with (bio)geochemical reactions is to couple by means of an operator-splitting approach two completely separate codes, one for variably-saturated flow and solute transport and one for equilibrium and kinetic biogeochemical reactions. This paper evaluates the accuracy of the operator-splitting approach for multicomponent systems for typical soil environmental problems involving transient atmospheric boundary conditions (precipitation, evapotranspiration) and layered soil profiles. The recently developed HP1 code was used to solve the coupled transport and chemical equations. For steady-state flow conditions, the accuracy was found to be mainly a function of the adopted spatial discretization and to a lesser extent of the temporal discretization. For transient flow situations, the accuracy depended in a complex manner on grid discretization, time stepping and the main flow conditions (infiltration versus evaporation). Whereas a finer grid size reduced the numerical errors during steady-state flow or the main infiltration periods, the errors sometimes slightly increased (generally less than 50%) when a finer grid size was used during periods with a high evapotranspiration demand (leading to high pressure head gradients near the soil surface). This indicates that operator-splitting errors are most significant during periods with high evaporative boundary conditions. The operator-splitting errors could be decreased by constraining the time step using the performance index (the product of the grid Peclet and Courant numbers) during infiltration, or the maximum time step during evapotranspiration. Several test problems were used to provide guidance for optimal spatial and temporal discretization.

Adsorption↗
PubMed2006

Effect of chitosan on the growth of human colonic bacteria.

Growth of 6 bacterial strains representing dominant members of the human colonic microflora was measured in the presence of 0.025, 0.05 and 0.5 % chitosan (from shrimp shells, with a 97 % final degree of deacetylation). The effect of chitosan was variable and dependent on bacterial species. The most susceptible to chitosan were bacteria belonging to genera Bacteroides and Clostridium (91-97% growth inhibition). On the other hand, Roseburia sp., Eubacterium sp. and Faecalibacterium sp. were more resistant (63-83 % inhibition of growth). Chitosan can thus be considered as one of the means for influencing the bacterial population in the human colon.

Anti-Bacterial Agents↗
PubMed2005

Impact of rainfall intensity on the transport of two herbicides in undisturbed grassed filter strip soil cores.

Two series of displacement experiments with isoproturon and metribuzin herbicides were performed on two undisturbed grassed filter strip soil cores, under unsaturated steady-state flow conditions. Several rainfall intensities (0.070, 0.147, 0.161, 0.308 and 0.326 cm h(-1)) were used. A water tracer (bromide) was simultaneously injected in each displacement experiment. A descriptive analysis of experimental breakthrough curves of bromide and herbicides combined with a modeling analysis showed an impact of rainfall intensity on the solute transport. Two contrasting physical non-equilibrium transport processes occurred. Multiple (three) porosity domains contributed to flow at the highest rainfall intensities, including preferential flow through macropore pathways. Macropores were not active any longer at intermediate and lowest velocities, and the observed preferential transport was described using dual-porosity-type models with a zero or low flow in the matrix domain. Chemical non-equilibrium transport of herbicides was found at all rainfall intensities. Significantly higher estimated values of degradation rate parameters as compared to batch data were correlated with the degree of non-equilibrium sorption. Experimental breakthrough curves were analyzed using different physical and chemical equilibrium and non-equilibrium transport models: convective-dispersive model (CDE), dual-porosity model (MIM), dual-permeability model (DP), triple-porosity, dual permeability model (DP-MIM); each combined with both chemical instantaneous and kinetic sorption.

Diffusion↗
PubMed2004

Chitinolytic enzymes from Clostridium aminovalericum: activity screening and purification.

A strain isolated from the feces of takin was identified as Clostridium aminovalericum. In response to various types of chitin used as growth substrates, the bacterium produced a complete array of chitinolytic enzymes: chitinase ('endochitinase'), exochitinase, beta-N-acetylglucosaminidase, chitosanase and chitin deacetylase. The highest activities of chitinase (536 pkat/mL) and exochitinase (747 pkat/mL) were induced by colloidal chitin. Fungal chitin also induced high levels of these enzymes (463 pkat/mL and 502 pkat/mL, respectively). Crab shell chitin was the best inducer of chitosanase activity (232 pkat/mL). The chitinolytic enzymes of this strain were separated from culture filtrate by ion-exchange chromatography on the carboxylic sorbent Polygran 27. At pH 4.5, some isoforms of the chitinolytic enzymes (30% of total enzyme activity) did not bind to Polygran 27. The enzymes were eluted under a stepwise pH gradient (pH 5-8) in 0.1 mol/L phosphate buffer. At merely acidic pH (4.5-5.5), the adsorbed enzymes were co-eluted. However, at pH close to neutral values, the peaks of highly purified isoforms of exochitinases and chitinases were isolated. The protein and enzyme recovery reached 90%.

Acetylglucosaminidase↗
PubMed2002

Identification and characterization of Clostridium paraputrificum, a chitinolytic bacterium of human digestive tract.

A strictly anaerobic, mesophilic and chitinolytic bacterial strain was isolated from human feces. Based on morphological and physiological properties and 16S rRNA sequence analysis the strain was identified as Clostridium paraputrificum. The strain utilized chitin and N-acetyl-D-glucosamine, grew on glucose and hydrolyzed starch. Cultivation of the strain with colloidal chitin as the growth substrate resulted in the production of gas (hydrogen and carbon dioxide) and formation of acetate and lactate (21.6 and 18.9 mmol/L, respectively) and only small quantities of propionate and butyrate (1.7 and 2.6 mmol/L, respectively). In the course of a 10-d cultivation with chitin, the endochitinase activity was detected after 1 d and gradually increased, reaching maximum after 3 d (251 nkat/L N-acetyl-D-glucosamine). The beta-N-acetylglucosaminidase activity appeared just at the beginning of the cultivation, increased to day 2 and then remained nearly constant. More than 90% of chitin added was degraded within 2 d of cultivation. On the zymogram of the extracellular chitinolytic complex were visible at least 6 isoenzymes with molar mass 43.5-65.0 kDa. The temperature optimum of endochitinase and beta-N-acetylglucosaminidase activities was 50 degrees C; the optimum activity of both enzymes was found at pH 4-6.

Anaerobiosis↗
PubMed2001

Chitinolytic bacteria of the mammal digestive tract.

Chitinolytic bacteria were isolated from the digestive tract of different mammals and characterized. All isolates were facultatively anaerobic, long Gram-positive, straight rods resembling Clostridium sp. Only one isolate consisted of Gram-positive ovoid cells. All cultures grew on glucose, N-acetylglucosamine, glucosamine, galactose, starch, hemicellulose and xylan. Fermentation products were mainly formate, acetate, butyrate and lactate. The isolates were identified as Clostridium sartagoforme (2 species), C. aminovalericum, C. bifermentans and Enterococcus durans (1 isolate of each species). Exocellular fractions of all strains exhibited higher activities of all enzymes than cellular ones. Inductive effects of hemicelluloses, pectin and laminarine on chitinases were demonstrated. High exocellular endochitinase activity was found in cultures grown on chitin. N-Acetylglucosaminidase activity was low with the exception of exocellular fractions of two strains of C. sartagoforme.

Animals↗
PubMed2001

Effects of central infusions of neuropeptide Y on the somatotropic axis in sheep fed on two levels of protein.

Effects of infusions of neuropeptide Y (NPY) into 3rd ventricle of growing sheep fed on diets containing restricted (R) or elevated (E) levels of protein on the immunoreactive (ir) somatostatin neurones, ir somatotrophs, growth hormone (GH) concentration in the blood plasma were studied. The long-term restriction of protein in the diet elicited: enhancing irSS content in periventricular perikarya; diminishing irSS stores in the median eminence and elevating the number ir somatotrophs and content of irGH. NPY infusions enhanced the content of irSS in perikarya in sheep fed on E diet and diminished the number of ir somatotrophs and content of irGH of sheep fed on R diet. The R diet as well as NPY infusions caused an increase in GH mean concentrations in the blood plasma. Obtained results suggest that stimulatory effect of restricted feeding and/or NPY action on GH secretion can be due to attenuated SS output. Since dietary restrictions and exogenous NPY have similar influence on the activation of GH secretion, we suggest that NPY could be a neuromodulatory link between nutritional cues and somatotropic axis in sheep.

Animals↗
PubMed1995

[The effect of virginiamycin on rumen fermentation in vitro after adaptation of donors to the inoculum].

Virginiamycin is an antibiotic active against grampositive bacteria in the alimentary tract, which is also suitable for supplementation of diets of growing and finishing ruminants. The aim of this work was to specify the effect of virginiamycin on some parameters of rumen fermentation in vitro with inoculi taken from wethers adapted or non-adapted to the virginiamycin intake. Incubations were performed anaerobically at 39 degrees C in serum bottles closed with Bunsen valves. Virginiamycin was added at 0 or 10 mg/l to the rumen fluid diluted with McDougall buffer. Virginiamycin significantly decreased production and utilization of lactic acid, production of methane and decomposition of casein when rumen fluid was taken from non-adapted wethers. Most of its effects disappeared when rumen fluid was sampled from wethers adapted to the virginiamycin intake (100 mg per head daily for 2 months). Adaptation of wethers to virginiamycin was further confirmed by analyses of the rumen fluid which was used for inoculation of in vitro cultures. Molar percentages of acetate, propionate, butyrate and valerate were the same before and after the adaptation. Therefore it can be concluded that the effects of virginiamycin on rumen parameters are not stable and its addition to ruminant diets cannot be recommended, with exception of the milk nutrition period. In the last experiment the stability of virginiamycin in the rumen fluid of adapted wethers was investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1993

Monensin has no effect on growth and metabolism of Megasphaera elsdenii.

A rumen strain of Megasphaera elsdenii was grown on glucose and lactate in monensin-free and monensin-supplemented medium (10 mg/L). Monensin had no effect on growth rate, growth yields, metabolic pattern and composition of cells. Growth yields of dry matter and protein were higher in cultures supplied with glucose than in cultures supplied with lactate. The bacterium compensated the lower gain of energy from fermentation of lactate by rapid utilization of this substrate. Cells grown on glucose contained more saccharide and less protein than lactate-grown cells.

Animals↗
PubMed1992

[Body weight and selected hematologic and biochemical parameters in calves fed various diets during milk feeding].

The objective of the present paper was to obtain haematological and biochemical parameters of calves during their milk feeding. Another goal was to compare a current feed ration containing the commercial feed mixture Biosan with two alternative rations comprising skimmed milk and fat supplement. The effect of milk drink acidification and the effect of the physical form of fat added to skimmed milk were investigated. the calves were divided into six groups, by 6 to 8 calves each (P1-Biosan, PP1-acid variant, P2-skimmed milk+fat concentrate powder KMKS, PP2-acid variant, P3-skimmed milk+fat paste, PP3-acid variant). The highest average daily liveweight gains were recorded in calves fed on unacidified skimmed milk with fat paste supplement (1.074 kg)-Tab. I. The highest average daily liveweight gains were observed in calves fed on fat paste enriched milk drink (P3) while the calves administered milk with fat concentrate powder (P2) had only slightly higher average daily weight gains than the calves on Biosan diet (group P1). The growth of daily weight gains as a result of diets containing acidified milk (PP1 and PP2) is also a positive finding; this growth is even statistically significant in the former case (P < 0.05). The calves showed hypohaemoglobinaemia from the beginning of the experiment (51.3-69.0 g/l) and the low haematocrit value (0.29-0.43 l/l), Tab. II, while the plasma iron level was paradoxically high (Tab. V).(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗
PubMed1991

Influence of redox potential on metabolism of glucose in mixed cultures of rumen microorganisms.

The rumen inocula taken from cows and sheep were incubated in pH controlled anaerobic batch cultures and the effect of the elevated redox potential (Eh) on metabolism of glucose was examined. In Eh regulated cultures (Eh = +100 mV) the VFA production and production of methane were decreased with a concomitant increase of production of lactate. In these cultures counts of lactilytic bacteria tended to be lower and counts of lactic acid bacteria higher than in cultures with a normal Eh. The elevated Eh also exerted an inhibitory effect on the rumen protozoa. The relevance of these changes to the rumen metabolism is discussed.

Animals↗
PubMed1989

The effect of monensin on in vitro utilization of lactate in the rumen contents.

The effect of monensin on the in vitro utilization of lactate in the rumen contents of a steer, cow and two wethers was investigated. The rate of the utilization of lactate in monensin-treated cultures was on average only two thirds of that found in cultures without monensin. Monensin tended to increase acetate and to decrease butyrate in cultures with lactate. After 11-week adaptation of a wether to monensin the inhibitory effect of ionophore persisted, being, however, less pronounced and without influence on the molar percentages of VFA. Effects of monensin reported here seem to be caused by its inhibiting action against rumen lactilytic protozoa. There were no significant differences between monensin from Elanco and the Czechoslovak analogue.

Animals↗
PubMed1988

Production of acids from inulin by a mixed culture of rumen microorganisms.

The production of volatile fatty acids (VFA) and lactic acid from inulin (plant fructan with 2-1 bonds) in in vitro rumen fermentations was followed. The experiments were performed with inocula from wethers receiving two rations, with two pH regimes and using as inocula either whole rumen contents or the corresponding rumen fluid. The following results were obtained: The VFA production was higher when using inocula from hay and concentrate fed wethers. In contrast to this, the lactic acid production was higher when using inocula from hay fed wethers. The VFA production tends to be higher in a weakly acid medium than in a neutral medium. Acetate-to-propionate molar ratio was lower at lower pH. The amounts and composition of the VFA were not different when using both types of inocula. Thus, we believe that micro-organisms colonising plant fibres obviously do not play an important role in inulin splitting.

Animal Feed↗
PubMed1985

Amino acid sequence homology between protein products of oncogenes and hormones (v-myc--gastrin and oxytocin; v-sis--secretin).

Computer comparisons of amino acid sequences from 8 retroviral oncogenes and 26 protein hormones were done with respect to structure similarity and so-called uninterrupted structure similarity. Sequence homology was found between v-myc, the transforming protein of MC29 virus, and human gastrin and oxytocin on the one hand, and between v-sis, the transforming protein of simian sarcoma virus, and secretin on the other.

Amino Acid Sequence↗
PubMed1980

[The effect of nitrovin on the kinetics of sulphadimidine in domestic fowl of different ages].

In experiment on cockerels, the interaction of sulphadimidine with nitrovin manifested itself in an effect on the distribution of sulphadimidine, and particularly on its bloodlevel; this depended, among other factors, on the age of the animals. At nitrovin medication, the bloodlevels of sulphadimidine were higher, mainly soon after administration, and their drop was quicker than in untreated animals. This effect on the levels of sulphadimidine in the blood was pronounced in three-week-old chickens, whereas in older birds it was feeble or absent. Except the higher level 30 min. after application to.five-week-old chickens given feed with 120 g t-1 of nitrovin, the differences were statistically insignificant. The changes in the concentration of sulphonamide in the liver and kidneys corresponded with the changes observed in the blood; the concentration in muscle was not affected by nitrovin under the given conditions. The favourable effect of nitrovin on weight gains, demonstrated in principle during the experiment, was directly dependent upon the concentration of nitrovin in feed. As to the effect of the length of its administratiion, the three-day administration of nitrovin (before weighing) to cockerels up to five weeks of age had a better influence on gains than administration from the sixth day after the medicated of the chickens. In older cockerels the gains were better in the groups treated for a longer time, i. e. from the sixth day from hatching.

Age Factors↗