Metabolism of aflatoxin, ochratoxin, zearalenone, and three trichothecenes by intact rumen fluid, rumen protozoa, and rumen bacteria

The effect of rumen microbes on six mycotoxins (aflatoxin B1, ochratoxin A, zearalenone, T-2 toxin, diacetoxyscirpenol, and deoxynivalenol ) considered to be health risks for domestic animals was investigated. The mycotoxins were incubated with intact rumen fluid or fractions of rumen protozoa and bacteria from sheep and cattle in the presence or absence of milled feed. Rumen fluid had no effect on aflatoxin B1 and deoxynivalenol . The remaining four mycotoxins were all metabolized, and protozoa were more active than bacteria. Metabolism of ochratoxin A, zearalenone, and diacetoxyscirpenol was moderately or slightly inhibited by addition of milled feed in vitro. The capacity of rumen fluid to degrade ochratoxin A decreased after feeding, but this activity was gradually restored by the next feeding time. Ochratoxin A was cleaved to ochratoxin alpha and phenylalanine; zearalenone was reduced to alpha-zearalenol and to a lesser degree to beta-zearalenol; diacetoxyscirpenol and T-2 toxin were deacetylated to monoacetoxyscirpenol and HT-2 toxin, respectively. Feeding of 5 ppm (5 mg/kg) of ochratoxin A to sheep revealed 14 ppb (14 ng/ml) of ochratoxin A and ochratoxin alpha in rumen fluid after 1 h, but neither was detected in the blood. Whether such conversions in the rumen fluid may be considered as a first line of defense against toxic compounds present in the diet is briefly discussed.     

Metabolism of aflatoxin, ochratoxin, zearalenone, and three trichothecenes by intact rumen fluid, rumen protozoa, and rumen bacteria.

The effect of rumen microbes on six mycotoxins (aflatoxin B1, ochratoxin A, zearalenone, T-2 toxin, diacetoxyscirpenol, and deoxynivalenol ) considered to be health risks for domestic animals was investigated. The mycotoxins were incubated with intact rumen fluid or fractions of rumen protozoa and bacteria from sheep and cattle in the presence or absence of milled feed. Rumen fluid had no effect on aflatoxin B1 and deoxynivalenol . The remaining four mycotoxins were all metabolized, and protozoa were more active than bacteria. Metabolism of ochratoxin A, zearalenone, and diacetoxyscirpenol was moderately or slightly inhibited by addition of milled feed in vitro. The capacity of rumen fluid to degrade ochratoxin A decreased after feeding, but this activity was gradually restored by the next feeding time. Ochratoxin A was cleaved to ochratoxin alpha and phenylalanine; zearalenone was reduced to alpha-zearalenol and to a lesser degree to beta-zearalenol; diacetoxyscirpenol and T-2 toxin were deacetylated to monoacetoxyscirpenol and HT-2 toxin, respectively. Feeding of 5 ppm (5 mg/kg) of ochratoxin A to sheep revealed 14 ppb (14 ng/ml) of ochratoxin A and ochratoxin alpha in rumen fluid after 1 h, but neither was detected in the blood. Whether such conversions in the rumen fluid may be considered as a first line of defense against toxic compounds present in the diet is briefly discussed.     

Practical identifiability of growth and substrate consumption models

The estimation of parameters in several dynamic models, which describe growth and substrate consumption, has been carried out using a modified Gauss-Newton-type method. The four models considered are Monod, Contois, linear specific growth rate, and an enzyme kinetic model. The initial values of the differential equations are included in the parameter vector which will be estimated. The efficiency of the method and the confidence limits of the parameters were studied using simulated measurement noise. The experimental results describe Trichoderma viride growing on glucose as the main carbon source.     

Laboratory Diagnosis of Canine Pyometra

The principal laboratory test used to confirm the pyometra diagnosis in the bitch has been the determination of the total white blood cell count in venous blood. A marked elevation is known to be a characteristic of the disease. In the present study, the white blood cell count was determined as well as the γ-globulin level. An elevation of the γ-globulin level and the total white blood cell count was very characteristic to the pyometra patients. The increase in the number of white blood cells nor the high γ-globulin level cannot be regarded specific for pyometra, therefore it was regarded important to find out a more specific test for pyometra. When sonicated E. coli bacteria were tested against sera from pyometra patients in electroimmunodiffusion, the precipitation was almost always detected when E. coli had been isolated from the uterus. This technique provides a quick method in detecting the causative E. coli infection. The present study suggests that whenever laboratory tests are used to confirm the pyometra diagnosis by the total white blood cell count, it is advantageous to analyze the total γ-globulin level in the serum as well as specific antibodies against a common E. coli antigen. Because of the reliability of the glutaraldehyde coagulation test and the simple technique, this can be suggested as the method of choice for an average small animal practice.     

Intrinsic properties of so-called dormant probiotic bacteria, determined by flow cytometric viability assays

Plate counting and four culture-independent flow cytometric assays were used to determine the viability and intrinsic properties of three probiotic strains during storage. The strains showed reduction in plate counts but were able to maintain esterase activity, intact cytoplasmic membrane, and pH gradient. The apparently uncultivable probiotic cells were active and stress resistant.     

Effects of raised CO2 on potential CH4 production and oxidation in, and CH4 emission from, a boreal mire

1 In a glasshouse experiment we studied the effect of raised CO₂ concentration (720 p.p.m.) on CH₄ emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17–20 °C). The potential for CH₄ production and oxidation was measured at the end of the emission experiment.
2 The vascular cores ('Sedge') consisted of a moss layer with sedges, and the moss cores (' Sphagnum ') of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6–12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH ₄ from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures.
3 In both Sedge and Sphagnum samples, CO₂ treatment doubled the potential CH₄ production but had no effect on the potential CH₄ oxidation. A raised concentration of CO₂ increased CH₄ efflux weakly and only at the highest peat temperatures (17–20 °C).
4 The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO₂ concentrations, and would thus retard any consequent increase in CH₄ emission.     

Seasonal variation in CH4 emissions and production and oxidation potentials at microsites on an oligotrophic pine fen

 Temporal and spatial variation in CH₄ emissions was studied at hummock, Eriophorum lawn, flark and Carex lawn microsites in an oligotrophic pine fen over the growing season using a static chamber method, and CH₄ production and oxidation potentials in peat profiles from hummock and flark were determined in laboratory incubation experiments. Emissions were lowest in the hummocks, and decreased with increasing hummock height, while in the lawns and flarks they increased with increasing sedge cover. Statistical response functions with water table and peat temperature as independent variables were calculated in order to reconstruct seasonal CH₄ emissions by reference to the time series for peat temperature and water table specific to each microsite type. Mean CH₄ emissions in the whole area in the snow-free period of 1993, weighted in terms of the proportions of the microsites, were 1.7 mol CH₄ m^–2. Potential CH₄ production and oxidation rates were very low in the hummocks rising above the groundwater table, but were relatively similar when expressed per dry weight of peat both in the hummocks and flarks below the water table. The CH₄ production potential increased in autumn at both microsites and CH₄ oxidation potential seemed to decrease. The decrease in temperature in autumn certainly reduced in situ decomposition processes, possibly leaving unused substrates in the peat, which would explain the increase in CH₄ production potential. Received: 16 August 1996 / Accepted: 30 November 1996     

Intrinsic Properties of So-Called Dormant Probiotic Bacteria, Determined by Flow Cytometric Viability Assays

Plate counting and four culture-independent flow cytometric assays were used to determine the viability and intrinsic properties of three probiotic strains during storage. The strains showed reduction in plate counts but were able to maintain esterase activity, intact cytoplasmic membrane, and pH gradient. The apparently uncultivable probiotic cells were active and stress resistant.     

Phenotypic plasticity in growth and fecundity induced by strong population fluctuations affects reproductive traits of female fish

Fish are known for their high phenotypic plasticity in life‐history traits in relation to environmental variability, and this is particularly pronounced among salmonids in the Northern Hemisphere. Resource limitation leads to trade‐offs in phenotypic plasticity between life‐history traits related to the reproduction, growth, and survival of individual fish, which have consequences for the age and size distributions of populations, as well as their dynamics and productivity. We studied the effect of plasticity in growth and fecundity of vendace females on their reproductive traits using a series of long‐term incubation experiments. The wild parental fish originated from four separate populations with markedly different densities, and hence naturally induced differences in their growth and fecundity. The energy allocation to somatic tissues and eggs prior to spawning served as a proxy for total resource availability to individual females, and its effects on offspring survival and growth were analyzed. Vendace females allocated a rather constant proportion of available energy to eggs (per body mass) despite different growth patterns depending on the total resources in the different lakes; investment into eggs thus dictated the share remaining for growth. The energy allocation to eggs per mass was higher in young than in old spawners and the egg size and the relative fecundity differed between them: Young females produced more and smaller eggs and larvae than old spawners. In contrast to earlier observations of salmonids, a shortage of maternal food resources did not increase offspring size and survival. Vendace females in sparse populations with ample resources and high growth produced larger eggs and larvae. Vendace accommodate strong population fluctuations by their high plasticity in growth and fecundity, which affect their offspring size and consequently their recruitment and productivity, and account for their persistence and resilience in the face of high fishing mortality.     

Intersubunit bridge formation governs agonist efficacy at nicotinic acetylcholine α4β2 receptors: unique role of halogen bonding revealed

The α4β2 subtype of the nicotinic acetylcholine receptor has been pursued as a drug target for treatment of psychiatric and neurodegenerative disorders and smoking cessation aids for decades. Still, a thorough understanding of structure-function relationships of α4β2 agonists is lacking. Using binding experiments, electrophysiology and x-ray crystallography we have investigated a consecutive series of five prototypical pyridine-containing agonists derived from 1-(pyridin-3-yl)-1,4-diazepane. A correlation between binding affinities at α4β2 and the acetylcholine-binding protein from Lymnaea stagnalis (Ls-AChBP) confirms Ls-AChBP as structural surrogate for α4β2 receptors. Crystal structures of five agonists with efficacies at α4β2 from 21-76% were determined in complex with Ls-AChBP. No variation in closure of loop C is observed despite large efficacy variations. Instead, the efficacy of a compound appears tightly coupled to its ability to form a strong intersubunit bridge linking the primary and complementary binding interfaces. For the tested agonists, a specific halogen bond was observed to play a large role in establishing such strong intersubunit anchoring.