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At least 109 records · Page 6Linked to original sources
PubMed1971

Parameters of rumen fermentation in a continuously fed sheep: evidence of a microbial rumination pool.

The feed and feces of a continuously fed sheep were analyzed for carbon, hydrogen, and nitrogen, with oxygen as the remainder. The daily feed-feces weight difference was used as the reactant in an equation representing the rumen fermentation. The measured products were the daily production of volatile fatty acids (VFA), CH(4), CO(2), and ammonia. The carbon unaccounted for was assumed to be in the microbial cell material produced in the rumen and absorbed before reaching the feces. The ratio of C to H, O, and N in bacteria was used to represent the elemental composition of the microbes formed in the rumen fermentation, completing the following equation:C(20.03)H(36.99)O(17.406)N(1.345) + 5.65 H(2)O --> C(12)H(24)O(10.1) + 0.83 CH(4) VFA + 2.76 CO(2) + 0.50 NH(3) + C(4.44)H(8.88)O(2.35)N(0.785) microbial cells absorbed With C arbitrarily balanced and O balanced by appropriate addition of water, any error is reflected in the H. The H recovery was 98.5%. The turnover rate constant for rumen liquid equilibrating with polyethylene glycol (PEG) was 2.27 per day. Direct counts and volume measurements of the individual types of bacteria and protozoa in the rumen were used to calculate the total microbial cell volume in the rumen, not equilibrating with it. The dry matter in the rumen (582 g) and the nitrogen content (12.05) of the microbes in the rumen were estimated, the latter constituting 85% of the measured N in the rumen. Calculations for rumen dry matter and nitrogen turning over at the PEG rate introduce big discrepancies with other parameters; a rumination pool must be postulated. Its size and composition are estimated. Arguments are presented to support the view that dry matter and some of the microbes, chiefly the protozoa, do not leave the rumen at the PEG rate. One experiment with the same sheep fed twice daily showed significantly less production of microbial cells than did the continuous (each 2 hr) feeding. Analysis of the microbial cell yield suggests that, on the basis of 11 mg of cells per adenosine triphosphate molecule, a maximum of six adenosine triphosphate molecules could have been formed from each molecule of hexose fermented.

Ammonia↗
PubMed2000

Rapid virus production and removal as measured with fluorescently labeled viruses as tracers.

Pelagic marine viruses have been shown to cause significant mortality of heterotrophic bacteria, cyanobacteria, and phytoplankton. It was previously demonstrated, in nearshore California waters, that viruses contributed to up to 50% of bacterial mortality, comparable to protists. However, in less productive waters, rates of virus production and removal and estimates of virus-mediated bacterial mortality have been difficult to determine. We have measured rates of virus production and removal, in nearshore and offshore California waters, by using fluorescently labeled viruses (FLV) as tracers. Our approach is mathematically similar to the isotope dilution technique, employed in the past to simultaneously measure the release and uptake of ammonia and amino acids. The results indicated overall virus removal rates in the dark ranging from 1.8 to 6.2% h(-1) and production rates in the dark ranging from 1.9 to 6.1% h(-1), corresponding to turnover times of virus populations of 1 to 2 days, even in oligotrophic offshore waters. Virus removal rates determined by the FLV tracer method were compared to rates of virus degradation, determined at the same locations by radiolabeling methods, and were similar even though the current FLV method is suitable for only dark incubations. Our results support previous findings that virus impacts on bacterial populations may be more important in some environments and less so in others. This new method can be used to determine rates of virus degradation, production, and turnover in eutrophic, mesotrophic, and oligotrophic waters and will provide important inputs for future investigations of microbial food webs.

Bacteria↗
PubMed2000

Transgenic animal models for virus-induced autoimmune diseases.

In the pathogenesis of autoimmune diseases, tolerance against self-determinants is lost and autoreactive lymphocytes are activated leading to pathological damage of single or multiple organs. Viral and other microbial infections have been implicated in these processes. Viruses may induce immunopathological damage by maintaining a chronic immune response against the locally persisting infectious agent. Alternatively, viruses may help to initiate anti-self immunoreactivity, e.g. by induction of an inflammatory milieu needed to overcome tolerance against self-antigens. Presentation of viral antigens and/or previously immunologically ignored self-antigens in secondary lymphoid organs is most probably the key event in the initiation of autoimmune diseases. Translocation of antigens to secondary lymphoid organs and primary induction of T cell responses is primarily mediated by dendritic cells (DCs). We discuss here two transgenic models of autoimmune diseases where DC-mediated antigen transport initiated autoimmune responses against microbial neoself antigens. In the first model, dose and timing of antigen delivery by DCs and turnover of antigenic peptides presented by DCs are the main parameters regulating the outcome of autoimmune diabetes. In the second model, chronic stimulation of organ-specific immune responses via DCs leads to severe cardiovascular immunopathology with arteritis, myocarditis and eventually dilated cardiomyopathy. Taken together, transgenic mouse models are valuable tools for delineating basic pathogenic mechanisms and evaluating therapeutic strategies to interfere with early detrimental processes that lead to manifest autoimmune diseases.

Animals↗
PubMed1983

Inhibition of hepatic protein degradation by synthetic analogues of chymostatin.

Analogues of the microbial proteinase inhibitor chymostatin have been synthesized. The two most promising analogues were tested on protein turnover in isolated rat hepatocytes. Their effect is much similar to the effect of chymostatin, but the analogues are even more powerful inhibitors, probably due to an increased effect on lysosomal thiol proteinases. The analogues blocked most of the lysosomal (i.e. methylamine-sensitive) degradation of endogenous protein and caused a 50% inhibition of the non-lysosomal degradation; the effect occurred rapidly and was reversed upon washing the cells. One of the analogues, Z-Arg-Leu-Phe(H), is the most potent inhibitor of hepatic protein degradation so far found.

Animals↗
PubMed1977

A contribution to a new test method for dandruff-inhibiting and "keratolytic" action of drugs.

Free cholesterol in lipids from the scalp and hair is predominantly a constituent of epidermal lipids. Therefore, a reduction in cholesterol content induced by a drug indicates a reduction in cell turnover in the epidermis. As, according to the literature, increased cell turnover in the epidermis results in formation of dandruff, a reduction in the proportion of cholesterol should indicate inhibition of the formation of dandruff. Conversely, an increase in free cholesterol should generally indicate a "keratolytic" effect. So unequivocal an interpretation has not so far been possible in persons with dandruff, as it was not known whether free cholesterol was increased or decreased. In addition, this interpretation was not possible after use of antimicrobial substances, as in vitro investigations had failed to exclude microbial esterification of cholesterol on the scalp. The present investigation has shown that correlation of free cholesterol level with cell turnover is permissible in patients with dandruff, even if antimicrobial drugs are being tested.

Adult↗
PubMed1997

Oxidation and assimilation of atmospheric methane by soil methane oxidizers.

The metabolism of atmospheric methane in a forest soil was studied by radiotracer techniques. Maximum (sup14)CH(inf4) oxidation (163.5 pmol of C cm(sup-3) h(sup-1)) and (sup14)C assimilation (50.3 pmol of C cm(sup-3) h(sup-1)) occurred at the A(inf2) horizon located 15 to 18 cm below the soil surface. At this depth, 31 to 43% of the atmospheric methane oxidized was assimilated into microbial biomass; the remaining methane was recovered as (sup14)CO(inf2). Methane-derived carbon was incorporated into all major cell macromolecules by the soil microorganisms (50% as proteins, 19% as nucleic acids and polysaccharides, and 5% as lipids). The percentage of methane assimilated (carbon conversion efficiency) remained constant at temperatures between 5 and 20(deg)C, followed by a decrease at 30(deg)C. The carbon conversion efficiency did not increase at methane concentrations between 1.7 and 1,000 ppm. In contrast, the overall methane oxidation activity increased at elevated methane concentrations, with an apparent K(infm) of 21 ppm (31 nM CH(inf4)) and a V(infmax) of 188 pmol of CH(inf4) cm(sup-3) h(sup-1). Methane oxidizers from soil depths with maximum methanotrophic activity respired approximately 1 to 3% of the assimilated methane-derived carbon per day. This apparent endogenous respiration did not change significantly in the absence of methane. Similarly, the potential for oxidation of atmospheric methane was relatively insensitive to methane starvation. Soil samples from depths above and below the zone with maximum atmospheric methane oxidation activity showed a dramatic increase in the turnover of the methane assimilated (>20 times increase). Physical disturbance such as sieving or mixing of soil samples decreased methane oxidation and assimilation by 50 to 58% but did not alter the carbon conversion efficiency. Ammonia addition (0.1 or 1.0 (mu)mol g [fresh weight](sup-1)) decreased both methane oxidation and carbon conversion efficiency. This resulted in a dramatic decrease in methane assimilation (85 to 99%). In addition, ammonia-treated soil showed up to 10 times greater turnover of the assimilated methane-derived carbon (relative to untreated soil). The results suggest a potential for microbial growth on atmospheric methane. However, growth was regulated strongly by soil parameters other than the methane concentration. The pattern observed for metabolism of atmospheric methane in soils was not consistent with the physiology of known methanotrophic bacteria.

Journal Article↗
PubMed2001

Butyrate suppression of colonocyte NF-kappa B activation and cellular proteasome activity.

Butyrate is derived from the microbial metabolism of dietary fiber in the colon where it plays an important role in linking colonocyte turnover and differentiation to luminal content. In addition, butyrate appears to have both anti-inflammatory and cancer chemopreventive activities. Using confocal microscopy and cell fractionation studies, butyrate pretreatment of a human colon cell line (HT-29 cells) inhibited the tumor necrosis factor-alpha (TNF-alpha)-induced nuclear translocation of the proinflammatory transcription factor NF-kappaB. Butyrate inhibited NF-kappaB DNA binding within 30 min of TNF-alpha stimulation, consistent with an inhibition of nuclear translocation. IkappaB.NF-kappaB complexes extracted from butyrate-treated cells were relatively resistant to in vitro dissociation by deoxycholate, suggesting a change in cellular IkappaB composition. Butyrate treatment increased p100 expression, an IkappaB that was not degraded upon TNF-alpha treatment. Butyrate also reduced the extent of TNF-alpha-induced IkappaB-alpha degradation and enhanced the presence of ubiquitin-conjugated IkappaB-alpha. The suppression of IkappaB-alpha degradation corresponded with a reduction in cellular proteasome activity as determined by in vitro proteasome assays and the increased presence of ubiquitin-conjugated proteins. The butyrate suppression of IkappaB-alpha degradation and proteasome activity may derive from its ability to inhibit histone deacetylases since the specific deacetylase inhibitor trichostatin A had similar effects. These results suggest a potential mechanism for the anti-inflammatory activity of butyrate and demonstrate the interplay between short chain fatty acids and cellular proteasome activity.

Active Transport, Cell Nucleus↗
PubMed1992

Glyphosate degradation by immobilized bacteria: field studies with industrial wastewater effluent.

Immobilized bacteria have been shown in the laboratory to effectively remove glyphosate from wastewater effluent discharged from an activated sludge treatment system. Bacterial consortia in lab columns maintained a 99% glyphosate-degrading activity (GDA) at a hydraulic residence time of less than 20 min. In this study, a pilot plant (capacity, 45 liters/min) was used for a field demonstration. Initially, activated sludge was enriched for microbes with GDA during a 3-week biocarrier activation period. Wastewater effluent was then spiked with glyphosate and NH4Cl and recycled through the pilot plant column during start-up. Microbes with GDA were enhanced by maintaining the pH at less than 8 and adding yeast extract (less than 10 mg/liter). Once the consortia were stabilized, the column capacity for glyphosate removal was determined in a 60-day continuous-flow study. Waste containing 50 mg of glyphosate per liter was pumped at increasing flow rates until a steady state was reached. A microbial GDA of greater than 90% was achieved at a 10-min hydraulic residence time (144 hydraulic turnovers per day). Additional studies showed that microbes with GDA were recoverable within (i) 5 days of an acid shock and (ii) 3 days after a 21-day dormancy (low-flow, low-maintenance) mode. These results suggest that full-scale use of immobilized bacteria can be a cost-effective and dependable technique for the biotreatment of industrial wastewater.

Biodegradation, Environmental↗
PubMed2005

The impact of saponins or saponin-containing plant materials on ruminant production--a review.

Saponins are steroid or triterpene glycoside compounds found in a variety of plants. Some saponin-containing plants, mainly legumes, have been used as animal feed, but others are toxic. Several studies on the effect of saponins on ruminant production have also been reported. Some in vitro and in vivo experiments that demonstrate the beneficial effects of saponin such as defaunation of the rumen and manipulation of the end products of fermentation are described. Defaunation is the selective removal of protozoa from the rumen microbial ecosystem by a cell membrane cholesterol-saponin interaction, which causes cell rupture. Because protozoa in the rumen cause protein turnover by predating on bacteria, defaunation increases the nitrogen utilization of the ruminant and may lead to an increase in growth, milk, or wool production. The growth-promoting effect was evident in the high roughage diet suggesting that the application of saponins or saponin-containing plant materials may be beneficial for the subsistence farmers in developing countries. Saponins are deglycosylated by rumen microbes. Some sapogenins have been detected in the digestive tract of ruminants; however, the direct action of these compounds on the host animal is still unclear. No information on the effects of saponin on ruminant reproduction is available. There is an urgent need for a systematic evaluation of the most active structural components of the saponins, and their interaction with the microbial community, the host animal, and the diet. Along with these studies, the direct effects of saponins or their microbial degradation products on the host must be examined in order to get the full understanding of the metabolism and beneficial effects of saponins on animals.

Animals↗
PubMed1978

Microbial transformation of polycyclic aromatic hydrocarbons in pristine and petroleum-contaminated sediments.

To determine rates of microbial transformation of polycyclic aromatic hydrocarbons (PAH) in freshwater sediments, C-labeled PAH were incubated with samples from both pristine and petroleum-contaminated streams. Evolved CO(2) was trapped in KOH, unaltered PAH and polar metabolic intermediate fractions were quantitated after sediment extraction and column chromatography, and bound cellular C was measured in sediment residues. Large fractions of C were incorporated into microbial cellular material; therefore, measurement of rates of CO(2) evolution alone would seriously underestimate transformation rates of [C]naphthalene and [C]anthracene. PAH compound turnover times in petroleum-contaminated sediment increased from 7.1 h for naphthalene to 400 h for anthracene, 10,000 h for benz(a)anthracene, and more than 30,000 h for benz(a)pyrene. Turnover times in uncontaminated stream sediment were 10 to 400 times greater than in contaminated samples, while absolute rates of PAH transformation (micrograms of PAH per gram of sediment per hour) were 3,000 to 125,000 times greater in contaminated sediment. The data indicate that four- and five-ring PAH compounds, several of which are carcinogenic, may persist even in sediments that have received chronic PAH inputs and that support microbial populations capable of transforming two- and three-ring PAH compounds.

Journal Article↗
PubMed2006

Practical applications of topical therapy for allergic, infectious, and seborrheic disorders.

Topical therapy is extremely important in the management of allergic, infectious, and seborrheic disorders. It can be used as a sole therapy or adjunctive therapy for these disorders, often minimizing the need for systemic therapy. In allergic diseases, pruritus can be decreased by removing allergen, desensitizing the skin or other antipruritic effects. Many agents can also maintain or replace moisture to the skin and have emollient effects. When used for infectious conditions, topical therapy can decrease microbial counts and reduce surface colonization of microbes and help to prevent relapses. Antiseborrheic products function by normalizing keratinocyte turnover rates by reducing epidermal division (keratoplastic), normalizing keratinization, and increasing desquamation (keratolytic). There are many different topical vehicles and modes of application: shampoos, whirlpools, soaks, rinses, sprays, lotions, gels, creams, and ointments. Shampoos are often the most practical and effective. The practitioner needs to become familiar with many active ingredients to learn what products are indicated for specific diseases.

Administration, Topical↗
PubMed1995

[Simulation of nutrient dynamics in the rumen of sheep and cattle considering the feed composition, level of feed intake and feeding frequency. 1. Model description].

The aim of this work was to develop a dynamic, mechanistic computer-model, which can be used to simulate digestion, outflow and pools of different nutrients in the rumen of sheep and cattle and which reacts on changes of the feed composition, on the level and the frequency of feeding. The model consists of 35 flux- and 17 differential equations and works under cyclic steady-state conditions. The following mechanism are integrated into the model: The three substrates protein, neutral detergent fibre (NDF) and non-fibre-carbohydrates are degraded by three specific groups of microbes. A fourth group degrades NDF and non-fibre-carbohydrates following the principle of competitive inhibition. The fermentation in the rumen serves for supply of energy for growth and for the maintenance of microbes. The rates of degradation are calculated from the turnover-time of the specific substrate and the amount of microbes. Recycling of N occurs through recycling of the microbial protein and the ruminohepatic pathway. If concentration of ammonia in rumen fluid decreases below 50 mg/l then the growth of microbes declines.

Animal Feed↗
PubMed1979

Macrophage heterogeneity.

Macrophages are a mobile, functionally diverse group of cells which may be recruited and stimulated to a high degree of metabolic activity. Heterogeneity may be detected from one site to another and result from local influences, e.g. lung v. peritoneal cells, or occur within a population and arise dur to different stages of differentiation, maturation or activation or possibly from distinct cell lines. Recruitment and turnover are important determinants of the diversity of cells at any one site. In addition, anti-tumour, anti-microbial and secretory capacities of macrophages are greatly influenced by the degree and nature of stimulation possibly affecting only a subpopulation of the cells. Accessory cell activity is also a function of a minor population of macrophages which have distinct surface antigens. The sources of the heterogeneity and the interrelationship between the macrophages subpopulations remain to be determined.

Animals↗
PubMed1999

Degradation of two protein sources at three solids retention times in continuous culture.

Effects of solids retention times (SRT) of 10, 20, and 30 h on protein degradation and microbial metabolism were studied in continuous cultures of ruminal contents. Liquid dilution rate was constant across all retention times at .12 h(-1) (8.3 h mean retention time). Two semipurified diets that contained either soybean meal (SBM) or alfalfa hay (ALFH) as the sole nitrogen source were provided in amounts that decreased as SRT was increased. Digestion coefficients for DM, NDF, and ADF increased with increasing SRT. Digestion coefficients for nonstructural carbohydrates were higher in the SBM diet than in the ALFH diet but were not affected by SRT. Protein degradation in the ALFH diet averaged 51% and was unaffected by retention time. In the SBM diet, digestion of protein was 77, 78, and 96% at 10-, 20-, and 30-h retention times, respectively. Microbial efficiency decreased with increasing SRT and was greater for the SBM than for the ALFH diet. Efficiencies ranged from 30.6 to 35.7 and 20.8 to 29.2 g of N/kg of digested DM for the SBM and ALFH diets, respectively, as SRT decreased from 30 to 10 h. The diaminopimelic acid content of the microbes increased as SRT increased, indicating that changes in microbial species occurred owing to passage rates. From these results, we concluded that the digestibility decreases associated with increased ruminal turnover rates may be less for nonstructural carbohydrates and protein than for the fiber fractions.

Animal Feed↗
PubMed1991

Effect of source and level of supplemental fat on total and ruminal organic matter and nitrogen digestion in dairy cows.

Effects of fat supplementation for dairy rations on digestibility and ruminal digestion were studied in four cows receiving a control diet (hay-concentrate) or this diet supplemented with 5 or 10% rapeseed oil or 10% tallow, according to a Latin square design. Neither total digestibility of DM, OM, and crude fiber nor ruminal OM digestibility was modified by lipid supply. Microbial N flow to the duodenum was calculated for solid-adherent bacteria and liquid-associated bacteria, using the turnover rate of liquid phase, the ruminal pools of bacteria and their concentrations in RNA, and diaminopimelic acid. Flows of total and bacterial duodenal OM and N did not depend on the fat content of the diet. In sacco ruminal degradation of DM was lower for a diet supplemented with 10% rapessed oil than for the control diet. The addition of rapeseed oil resulted in decreased acetate and increased propionate proportions in ruminal VFA and decreased ruminal ammonia after feeding. This trial showed that modifications in ruminal digestion did not have any negative consequence on OM degradation and did not modify ruminal N digestion.

Animal Feed↗
PubMed1976

Dynamics of fermentation of a purified diet and microbial growth in the rumen.

Ruminal fermentation and disappearance of glucose, starch, and cellulose, and incorporation of glucose and starch into microbial cells were estimated in a fistulated Jersey cow fed twice daily a purified diet containing urea as the sole nitrogen source. Estimated rumen volume was 59.8 liters. Turnover time and rate of passage of rumen contents were 33.4 h and 1.8 liters per h. Turnover times of glucose, starch, and cellulose were .17, 4.7, and 14.2 h. Fermentation times of glucose, starch, and cellulose were .17, 5.5, and 25.1 h. Percentages of glucose, starch, and cellulose utilized in the rumen were 99.4, 85.4, and 60.6. Thus, 18.5% of the carbohydrate fed bypassed rumen fermentation, and 81.5% was utilized in the rumen. All glucose disappeared from the rumen within an hour. An average of 32.1, 43.0, and 14%, respectively, of glucose utilized was incorporated into microbial cells, volatile fatty acids, and carbon dioxide. Percentage of starch incorporated into cells varied, with time being highest 2 h after feeding at 40% and lowest at 20%, 10 h after feeding. Respective percentages of starch incorporated into microbial cells, volatile fatty acids, and carbon dioxide were 32.4, 45.9; and 13.3. Total microbial protein and cell yields per kilogram carbohydrate utilized in the rumen were 77.1 and 117.5 g. Microbial cell yield per mole (estimated) of adenosine triphosphate was 16.2 g.

Adenosine Triphosphate↗