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PubMed2004

Evaluation of microbial phytase in broiler diets.

Two trials were conducted to evaluate the efficacy of a new microbial phytase (Phyzyme XP) for broiler chicks. Trial 1 used 192 8-d-old male broilers in a 14-d trial to assess growth and nutrient utilization. Dietary treatments (221.9 g/kg CP) included a positive control [5.0 g/kg nonphytate P (NPP)], negative control (1.2 g/kg NPP), and negative control plus 500 or 1,000 phytase units/kg of diet. Phytase addition increased weight gain, feed intake, feed efficiency, and tibia and toe ash (linear, P < 0.01) with tibia ash also responding quadratically (P < 0.05). Apparent ileal digestibility of P (linear and quadratic, P < 0.05), tryptophan, and valine (linear, P < 0.05) also increased. Linear and quadratic responses were observed for retention of DM, nitrogen, P, and several amino acids (P < 0.05) with added phytase. Trial 2 utilized 576 1-d-old male broilers over a 42-d period to evaluate growth performance. Diets were formulated for starter (222.7 g/kg CP) and grower (201.5 g/kg CP) phases and included a positive control (starter and grower, 5.0 and 3.8 g/kg NPP, respectively); negative control (starter and grower, 2.4 and 1.8 g/kg NPP, respectively); negative control plus 500, 750, or 1,000 phytase units/kg; and negative control plus 500 phytase units/kg of Natuphos phytase. Phytase increased weight gain and feed intake (starter, grower, overall) as well as feed efficiency during the starter period (linear, P < 0.05). Feed intake was also improved during the grower period and overall (quadratic, P < 0.05). Tibia and toe ash of birds fed for the first 21 d increased (linear, P < 0.05) with tibia ash also increasing quadratically (P < 0.05). Overall, tibia and toe ash were improved due to phytase addition (linear and quadratic, P < 0.05). In conclusion, this microbial phytase, derived from Escherichia coli and expressed in Schizosaccaromyces pombe, elicited improved growth performance, bone mineralization, and P utilization in broiler chicks.

6-Phytase↗
PubMed1993

[The effect of starch sources barley, maize and potatoes and their ration portions on the nutrient digestibility and energy utilization in ruminants. 4. Nitrogen metabolism in the rumen].

In 9 experimental periods on four adult bulls (LW 550 kg) fitted with re-entrant cannulae in the proximal duodenum isoenergetic rations were used on feeding level 1.7 with ground barley, ground maize or fresh potatoes as starch sources. The net energy parts of these concentrates in the ration amounted to 50, 25 and 10%. 50 to 80% of the ration DM consisted of dried grass and about 10% of sugar beet pulp. The dried grass supplied on an average 87, 79 and 62% of the feed crude protein. The intake of DM was 7.74 +/- 0.42 (mean +/- SD) kg/d. The energetic efficiency of microbial N synthesis in the rumen (g N/kg organic matter true fermented in the rumen, TFOM) was averaged 16.4 with a range of 10.6 to 21.4. The microbial efficiency achieved a maximum when the ratio of nitrogen-free extract to crude fibre in the diet was 1.7 and 2.1 with barley, 1.8 with potatoes and 2.1 and 3.3 with corn as starch source. Changes in the microbial efficiency were positively correlated with the rate of passage of non-microbial organic matter from the rumen (g/d) and with the duodenal flow rate (kg digesta/kg DM intake). The relation to the rate of carbohydrate fermentation in the rumen (in %) and to the amount of TFOM (g/d) was negative. The duodenal flow of microbial N and non-ammonia N (g/d) correlated negatively with the organic matter apparently fermented in the rumen (AFOM) and positively with the non AFOM. The amino acid (AA) profile of the duodenal protein was affected by the starch source. It was concluded that the metabolism of nitrogen in the forestomachs of cattle is affected by the source of starch and the ratio of forage to concentrate. There exists a relationship between both factors. The net synthesis of microbial protein in the rumen is not only the result of substrate fermentation. The passage of non-AFOM from the rumen significantly affects the energetic efficiency of microbial nitrogen synthesis and the duodenal supply of AA.

Amino Acids↗
PubMed1999

Rhizosphere feedbacks in elevated CO(2).

Understanding rhizosphere processes in relation to increasing atmospheric CO(2) concentrations is important for predicting the response of forest ecosystems to environmental changes, because rhizosphere processes are intimately linked with nutrient cycling and soil organic matter decomposition, both of which feedback to tree growth and soil carbon storage. Plants grown in elevated CO(2) substantially increase C input to the rhizosphere. Although it is known that elevated CO(2) enhances rhizosphere respiration more than it enhances root biomass, the fate and function of this extra carbon input to the rhizosphere in response to elevated CO(2) are not clear. Depending on specific plant and soil conditions, the increased carbon input to the rhizosphere can result in an increase, a decrease, or no effect on soil organic matter decomposition and nutrient mineralization. Three mechanisms may account for these inconsistent results: (1) the "preferential substrate utilization" hypothesis; (2) the "priming effect" hypothesis; and (3) the "competition" hypothesis, i.e., competition for mineral nutrients between plants and soil microorganisms. A microbial growth model is developed that quantitatively links the increased rhizosphere input in response to elevated CO(2) with soil organic matter decomposition. The model incorporates the three proposed mechanisms, and simulates the complexity of the rhizosphere processes. The model also illustrates mechanistically the interactions among nitrogen availability, substrate quality, and microbial dynamics when the system is exposed to elevated CO(2).

Journal Article↗
PubMed2005

Effect of carbohydrate source on ammonia utilization in lactating dairy cows.

This study was conducted to investigate the effect of dextrose, starch, NDF, and a carbohydrate (CHO) mix on utilization of ruminal ammonia in dairy cows. Four ruminally and duodenally cannulated Holstein cows (BW = 788 +/- 31 kg; 217 +/- 35 d in milk) were allocated to four treatments in a 4 x 4 Latin square design trial. Cows were fed an all alfalfa diet at 12-h intervals (DMI = 22.2 +/- 0.25 kg/d). Treatments were control, white oat fiber (NDF); corn dextrose (GLU); cornstarch (STA); and a CHO mix (25% of each): apple pectin, GLU, STA, and NDF (MIX). Carbohydrates were introduced intraruminally during feeding at 20% of dietary DMI. Ruminal ammonia was labeled with (15)N. Ruminal pH was the highest for NDF followed by STA and MIX and GLU (P < 0.001). Ruminal ammonia concentration and pool size were decreased by GLU and STA compared with NDF (P < 0.001 and P = 0.03, respectively). Acetate, isobutyrate, isovalerate, and total VFA concentration in the rumen were decreased (P = 0.009 to 0.001), and butyrate was increased (P < 0.001) by GLU compared with the other CHO. Microbial N flow to the duodenum was decreased (P < 0.05) by NDF compared with the other CHO, and the flow of microbial N formed from ammonia was greater for STA compared with GLU and NDF (P = 0.04 and 0.03, respectively). Urinary N loss was decreased (P = 0.05) by GLU and STA, but overall (feces plus urine) N losses were not affected (P = 0.73) by treatment. Milk urea concentration was lowered by GLU and STA compared with NDF and MIX (P = 0.002). The proportion of bacterial N synthesized from ammonia in the rumen was greater with STA than with NDF and MIX and was least for GLU (P = 0.02). Irreversible ammonia loss and flux were lower (P = 0.09 and 0.02, respectively) for GLU than for STA and NDF. As a percentage of the dose given, cumulative secretion of (15)N ammonia in milk protein was greater for STA than for GLU or NDF (P = 0.01 and 0.001, respectively). This experiment demonstrated that provision of readily fermentable energy can decrease ammonia concentrations in the rumen through decreased ammonia production (GLU), or through enhanced uptake of ammonia for microbial protein synthesis (STA). Rapidly fermentable energy in the rumen decreased ammonia production and flux, but the overall efficiency of ammonia utilization for milk protein synthesis was only increased by enhancing ruminal microbial ammonia uptake.

Ammonia↗
PubMed2001

Optimization of rate and efficiency of dietary nitrogen utilization through the use of animal by-products and(or) urea and their effects on nutrient digestion in Holstein steers.

The objective of this N balance study was to determine the potential for improving the efficiency and rate of dietary N utilization in Holstein steers by feeding an amino acid-balanced mixture of animal by-product protein sources in combination with urea. The Beef NRC 1996 Model Level 2 was used to formulate a corn-based (86:14 concentrate-hay) control diet with soybean meal as the primary N supplement that would provide ME and metabolizable protein (MP) allowable ADG of 1.4 kg in 250-kg steers with an estrogenic implant and fed an ionophore. A combination of porcine meat and bone meal, fish meal, hydrolyzed feather meal, and blood meal was also formulated as an undegradable intake protein (UIP) blend to complement those amino acids (AA) derived from microbial protein synthesis. Four steers with an average initial BW of 259 kg were assigned in a 4 x 4 Latin square design to treatments consisting of control, two levels of UIP inclusion (2.6 and 5.2%; DM basis) in combination with urea, and a negative control "urea diet" containing no UIP and no SBM. The steers were fed at hourly intervals 95% of ad libitum intake and were injected with 500 microg of estradiol-17beta twice daily. Nitrogen intakes were 155, 160, 162, and 145 g/d, and N balances were 47, 51, 42, and 47 g/d when the 0, 2.6, 5.2% UIP and the urea diets were fed, respectively. Nitrogen balance was reduced with the 5.2% UIP diet (P < 0.05), and was less than the capacity estimate derived from abosmasal casein infusion studies. Apparent N digestibilities averaged 69%, but DM, OM, and nonstructural carbohydrate digestibilities were significantly reduced for the urea diet. Feeding 5.2% UIP in the diet reduced (P < 0.05) the biological value from 46 to 38%, which was accompanied by a significant elevation of plasma urea N. Results indicate that genetic capacity for N retention was approximately 51 g/d. Results demonstrate that use of an AA-balanced blend of animal by-product protein sources did not improve the efficiency of dietary N usage when added to corn-based diets formulated with the Beef NRC 1996 Model Level 2 to meet nutrient requirements of rapidly growing steers. Using urea as the only N supplement achieved equal rate and efficiency of N use.

Animals↗
PubMed1966

Effects of inhibition and repression on the utilization of substrates by heterogeneous bacterial communities.

This investigation attempts to evaluate to what extent enzyme inhibition and repression by metabolites, indigenous to the cell, are significant phenomena in natural microbial communities. Three case histories of the kinetics of substrate utilization and growth in multisubstrate media by heterogeneous bacterial populations are presented: (i) concurrent substrate utilization and growth on both substrates simultaneously (glucose plus benzoate); (ii) sequential substrate elimination accompanied by diauxic growth as a result of inhibition of enzyme activity (glucose plus galactose); (iii) sequential substrate utilization accompanied by diauxic growth caused by repression of enzyme formation (glucose plus l-phenylalanine, benzoate plus l-phenylalanine). It is shown that enzyme inhibition was observed in two-substrate media as well as in multisubstrate media and was maintained at low substrate concentrations (few milligrams per liter). A special attempt has been made to maintain the diversity of the experimental microbial population during the adaptation and enrichment period. All substrates were determined with sensitive analytical methods specific for the individual substrates. The results obtained confirm that catabolite repression and the resulting sequential substrate utilization are observed in heterogeneous bacterial populations.

Acids↗
PubMed1989

Peptide uptake is essential for growth of Lactococcus lactis on the milk protein casein.

The chlorated dipeptide L-alanyl-beta-chloro-L-alanine (diACA) is very toxic for Lactococcus lactis. Spontaneous mutants resistant to the dipeptide were isolated from plates. The presence and activities of cell wall-associated proteinase, different peptidases in cell extracts, amino acid transport systems, and di- and oligopeptide transport systems were examined and compared in a diACA-resistant mutant and the wild type. Only the rates of di- and tripeptide transport were found to be significantly reduced in the diACA-resistant mutant of L. lactis ML3. Since all other characteristics of this mutant were comparable to those of the wild type, the diACA-resistant mutant is most likely deficient in di- and tripeptide transport. Uptake of di- and tripeptides by L. lactis ML3 was found to be mainly mediated by one peptide transport system. The peptide transport-deficient mutant was found to be unable to grow on a chemically defined medium supplemented with casein as the sole nitrogen source, whereas growth could be restored by the addition of amino acids. These results indicate that peptide transport in L. lactis ML3 is an essential component in the process of casein utilization during growth in milk.

Amino Acids↗
PubMed1993

Influence of level of urea and method of supplementation on characteristics of digestion of high-fiber diets by sheep.

Effects of level and method of urea supplementation of N utilization and characteristics of digestion of a N-deficient (.85% N), citrus pulp-based diet were evaluated in a 4 x 4 Latin square design experiment, using four ruminally and intestinally cannulated crossbred (D'man x Sardi) rams. Two levels of urea (15.1 and 8.8 g/d, providing total N intakes of 12.0 and 9.1 g/d, respectively) and two methods of supplementation (urea mixed with the diet or continuously infused in the rumen) were compared in a 2 x 2 factorial arrangement of treatments. Ruminal pH varied between 6.2 and 7.0 across treatments and tended (P > .10) to be lower in animals receiving urea infusion. Ruminal ammonia concentrations were lower (P < .01) and more stable with urea infusion than with urea feeding. Ruminal VFA concentrations and profiles were unaffected (P > .10) by treatments. Site and extent of OM and fiber digestion were not influenced (P > .10) by either level of urea in the diet or method of supplementation. Average ruminal OM and ADF digestion were 53.1 and 64.5%, respectively. Total tract digestion values averaged 75.9 and 73.5%, respectively. With the exception of N efficiency (duodenal nonammonia N/total N intake) that was 31% lower (P < .10) for the high- than for the low-urea treatment, there were no treatment responses or interactions (P > .10) on characteristics of N utilization. Microbial N flow to the small intestine averaged (across treatments) 9.0 g/d and constituted 87% of the nonammonia N leaving the abomasum.(ABSTRACT TRUNCATED AT 250 WORDS)

Ammonia↗
PubMed2005

Impacts of the source and amount of crude protein on the intestinal supply of nitrogen fractions and performance of dairy cows.

The objective of this article was to review and summarize the significance of the amount and source of dietary crude protein supplements on the supply of nitrogen fractions passing to the small intestine and the performance of lactating dairy cows. A meta-analysis was used to evaluate 2 data sets, one for nitrogen flow to the small intestine and one for performance of cows. The response of dairy cows to rumen-undegradable protein supplements is variable. A portion of this variable response from research trials is explained by the source of crude protein in the control diet, the proportion and source of rumen-undegradable protein in the experimental diet, the effect of rumen-undegradable protein on microbial protein outflow from the rumen, the degradability and amino acid content of the rumen-undegradable protein, and the crude protein percentage of the diet. Compared with soybean meal, the mean milk production responses to feeding rumen-undegradable protein supplements ranged from -2.5 to +2.75%. Because of the large variation and small magnitude of response when rumen-undegradable protein supplements are fed compared with soybean meal, efficiency of nitrogen utilization and the cost to benefit ratio for these crude protein supplements may determine the source and amount of crude protein to feed to dairy cows in the future.

Amino Acids↗
PubMed1985

Quantitative effects of defaunation on rumen fermentation and digestion in sheep.

Studies on the quantitative significance of protozoa on carbon and nitrogen digestion and metabolism in the rumen were carried out in sheep given a diet of pelleted concentrate (500 g/d) and chopped hay (500 g/d). Measurements were made of apparent digestibility; flows of organic matter and dietary and microbial non-ammonia N (NAN) (using 15NH4+) to the duodenum; and rates of production, interconversion and metabolism of the major C fermentation end-products (from mathematical modelling of 14C isotope values). The population density of bacteria in the rumen increased as a result of defaunation (28.6 compared with 8.2 X 10(9) organisms/ml). This high density was associated with greater utilization of volatile fatty acids (VFA) within the rumen. The rate of irreversible loss (IL) of bicarbonate + carbon dioxide from the rumen was greater in the defaunated animals (98.5 v. 57.2 g C/d) but the IL from the blood was greater in the faunated group (138.6 v. 106.1 gC/d). This is consistent with the hypothesis that the high population density of bacteria found in the rumen fluid of defaunated animals may result in increased fermentation of rumen VFA and digestible dietary carbohydrate, thereby increasing the output of CO2 from the rumen and reducing the quantity of VFA (hence energy) available to the host. There was no difference in the flow of organic matter (OM) to the duodenum but there was a higher faecal excretion of OM in defaunated animals (apparent OM digestibility: 0.72 in faunated, 0.67 in defaunated). Defaunation did not significantly increase the flow of NAN to the duodenum, the percentage of duodenal NAN of bacterial origin or the quantity of microbial NAN synthesized/g organic matter fermented. Faecal excretion of NAN was higher in defaunated animals (5.3 v. 3.6 g N/d).

Animals↗
PubMed2001

A metabolic node in action: chorismate-utilizing enzymes in microorganisms.

The shikimate pathway has been described as a metabolic tree with many branches that led to the synthesis of an extensive range of products. This pathway is present only in bacteria, fungi, and plants. While there is only little difference in the sequence of the chemical reactions of the pathway, significant differences exist in terms of organization and regulation. In the main trunk of the shikimate pathway, D-erythrose 4-phosphate and phosphoenolpyruvate are converted via shikimate to chorismate. Chorismate is the common precursor for the biosynthesis of the aromatic amino acids, phenylalanine, tyrosine, and tryptophan, but also for other products as diverse as folate cofactors, benzoid and naphthoid coenzymes, phenazines, and siderophores. Five chorismate-utilizing enzymes have been characterized in microorganisms: chorismate mutase, anthranilate synthase, aminodeoxychorismate synthase, isochorismate synthase, and chorismate pyruvate-lyase. In this review these enzymes are discussed in terms of the corresponding gene structures and regulation, nucleotide and protein sequences, protein structures, and reaction mechanisms. The main emphasis is on transcriptional and posttranslational regulatory mechanisms, in view of how a microbial cell exploits its chorismate pool in diverse anabolic pathways. Comparison of the chorismate-utilizing enzymes has shown that some of them share sequence similarity, suggesting divergent evolution and commonality in reaction mechanisms. However, other chorismate-utilizing enzymes are examples of convergent evolution toward similar reaction capabilities.

Anthranilate Synthase↗
PubMed1988

Protein metabolism in the rumen of silage-fed steers: effect of fishmeal supplementation.

1. Ryegrass (Lolium perenne cv. Cropper) silage was given to four Friesian steers (initial live weight (LW) 172 kg) alone or with a fishmeal supplement (150 g fresh weight/kg silage dry matter (DM)) in a balanced two-period change-over design. The dietary components were the same as those used in a recent experiment by Gill et al. (1987). All diets were offered hourly at 24 g DM/kg LW. 2. Fishmeal supplementation increased dietary nitrogen intake (P less than 0.01) and significantly increased the flow of total N (P less than 0.01), non-ammonia N (NAN) (P less than 0.01) and amino acids (P less than 0.05) at the duodenum. The increased supply of NAN to the duodenum was due largely (67%) to increased flow of undergraded dietary protein. 3. Microbial protein production was estimated simultaneously with 15N, diaminopimelic acid (DAPA) and a novel technique using L-[4,5-3H]leucine. Estimates varied with the marker and source of microbial isolate but mean values indicated that microbial N flow was significantly increased by fishmeal supplementation (P less than 0.05). The use of L-[4,5-3H]leucine as a microbial marker is justified and its possible advantages over other markers are discussed. 4. The efficiency of microbial protein synthesis was significantly increased from 30.8 g N/kg organic matter apparently digested in the rumen (OMADR) to 54.3 g N/kg OMADR by fishmeal supplementation (P less than 0.01). However, this indicates that relatively high efficiencies can be achieved with unsupplemented high quality silage supplied continuously. Rumen degradable N (RDN) supply was significantly increased by fishmeal supplementation (P less than 0.05) but apparent efficiency of capture of RDN by rumen microbes was not significantly increased. 5. Attempts were made to investigate the source of N utilized by the microbes on the two diets by intrarumen infusions of (15NH4)2SO4 and L-[4,5-3H]leucine but these were confounded by rumen-mixing problems. Findings obtained suggest that a lower proportion of microbial N may have been derived from rumen ammonia when the silage was supplemented with fishmeal but no differences in the extent of direct incorporation of leucine into microbial protein were observed. This could indicate an increase in microbial peptide uptake on the fishmeal-supplemented diet. However, evidence was also obtained suggesting that the improvement in microbial protein synthetic efficiency with supplementary fishmeal was also due to the provision of a more continuous supply of nitrogenous substrates for microbial growth, as a result of hourly feeding.(ABSTRACT TRUNCATED AT 400 WORDS)

Animal Feed↗
PubMed1989

Microbes of the avian cecum: types present and substrates utilized.

This paper discusses the types and properties of microorganisms found in avian ceca, with special reference to the chicken. Microbial activity in the cecum is primarily fermentative, but there has been little evidence of cellulose fermentation, and the predominant bacterial types are relatively inactive against other high-molecular-weight compounds of dietary origin. In all avian species examined, the consistent presence of large populations of uric acid-degrading bacteria supports the view that microbial populations in the ceca permit reabsorption of water and possibly nonprotein nitrogen from the backflow of urine. These capabilities may be of particular importance to wild birds under conditions of water and food deprivation.

Aging↗
PubMed2002

Effects of oscillating dietary protein on ruminal fermentation and site and extent of nutrient digestion in sheep.

Eight cannulated wethers (BW = 52.5 +/- 5.7 kg) were used in a replicated 4 x 4 Latin square designed experiment to evaluate the effects of oscillating dietary protein concentrations on ruminal fermentation, site and extent of digestion, and serum metabolite concentrations. Four treatments consisted of a 13, 15, or 17% CP diet fed daily or a regimen in which dietary CP was oscillated between 13 and 17% on a 48-h basis (ACP). All diets consisted of 65% bromegrass hay (10.5% CP, 61.9% NDF, 37.2% ADF) plus 35% corn-based supplement and were formulated to contain the same amount of degradable intake protein (9.6% of DM) plus additional undegradable intake protein (SoyPLUS, West Central Cooperative, Ralston, IA) to accomplish CP levels above 13%. Each of four experimental periods were 16 d in duration with 12 d for diet adaptation followed by 4 d for sample collection. All wethers were fed at 3.0% of initial BW (DM basis) throughout the experiment, resulting in an average organic matter intake of 1.39 kg/d across treatments. When compared to the 15% CP daily treatment, feeding ACP had no effect (P > or = 0.10) on ruminal or lower tract N, NDF, ADF, or OM digestion. True ruminal OM digestion responded quadratically (P = 0.07) to increasing dietary CP, reaching a maximum of 52.0% of OM intake with the 15% CP treatment. Sheep fed ACP tended to have lower (P = 0.08) ruminal NH3 N concentrations and an overall higher (P = 0.0001) molar proportion of acetate compared to those fed 15% CP daily. Total VFA concentrations were not affected (P > or = 0.45) by increasing dietary CP. Microbial efficiency did not differ (P > or = 0.55); thus, bacterial N flow at the duodenum responded quadratically (P = 0.04) to increasing dietary CP. Nonbacterial N (P = 0.001) and total N (P = 0.01) flows at the duodenum and total tract N digestibility (P < or = 0.04) increased linearly as dietary CP increased. Wethers fed ACP maintained a lower (P = 0.002) serum glucose and lower (P = 0.0006) serum urea N compared to those fed 15% CP daily. Because the CP content of the diet was increased at the expense of corn, the response to increased CP observed in this experiment is most likely due to negative associative effects of supplemental starch on ruminal fermentation and microbial growth. Oscillating the CP content of the diet on a 48-h basis has little effect on digestion or N utilization in sheep compared with feeding the same quantity of protein on a daily basis.

Animal Feed↗
PubMed1997

Biodegradation of the pesticide 4,6-dinitro-ortho-cresol by microorganisms in batch cultures and in fixed-bed column reactors.

A mixed culture of microorganisms able to utilize 4,6-dinitro-ortho-cresol (DNOC) as the sole source of carbon, nitrogen and energy was isolated from soil contaminated with pesticides and from activated sludge. DNOC was decomposed aerobically in batch cultures as well as in fixed-bed column reactors. Between 65% and 84% of the substrate nitrogen was released as nitrate into the medium, and 61% of the carbon from uniformly 14C-labelled DNOC was recovered as 14CO2. The mixed microbial culture also decomposed 4-nitrophenol and 2,4-dinitrophenol but not 2,3-dinitrophenol, 2,6-dinitrophenol, 2,4-dinitrotoluene, 2,4-dinitrobenzoic acid or 2-sec-butyl-4,6-dinitrophenol (Dinoseb). Maximal degradation rates for DNOC by the bacterial biofilm immobilized on glass beads in fixed-bed column reactors were 30 mmol day-1 (1 reactor volume)-1, leaving an effluent concentration of less than 5 micrograms l-1 DNOC in the outflowing medium. The apparent Ks value of the immobilized mixed culture for DNOC was 17 microM. Degradation was inhibited at DNOC concentrations above 30 microM and it ceased at 340 microM, possibly because of the uncoupling action of the nitroaromatic compound on the cellular energy-transducing mechanism.

2,4-Dinitrophenol↗
PubMedDate not supplied

Physiological properties and plasmid content of several strains of Azospirillum brasilense and A. lipoferum.

Four strains of Azospirillum brasilense, including strain 7000 (ATCC 29145) and five strains of A. lipoferum, including strain Br17 (ATCC 29709) were examined for the presence of plasmids. All the strains were found to harbour 1 to 5 plasmids whose molecular weight ranged from 3.5 to over 300 Md. No obvious relationship between the plasmids and phenotypic properties was established as yet, in particular N2 fixation, substrate utilization, drug resistance and lysogenic state. Six out of the 9 strains were lysogenic and phage production was inducible by mitomycin C. An icosahedric phage was purified from strain 7000.

Bacteria↗
PubMed1997

Effect of increasing proportion of supplemental nitrogen from urea on intake and utilization of low-quality, tallgrass-prairie forage by beef steers.

Five Angus x Hereford steers with ruminal and duodenal fistulas were used in a 5 x 5 Latin square to determine effects of increasing the proportion of urea in supplemental degradable intake protein (DIP) on intake, fermentation, and digestion. Steers had ad libitum access to low-quality, tallgrass-prairie forage (2.4% CP, 76% NDF). Supplemental DIP (380 g/d) was from sodium caseinate and(or) urea and was balanced with cornstarch to provide a final supplement (approximately 939 g DM/d) that contained 40% CP. The percentages of supplemental DIP from urea were 0, 25, 50, 75, and 100%. Intake of forage OM was not affected (P > or = .30) by urea level. Ruminal and total tract digestibilities of OM and NDF generally responded in a quadratic manner (P < or = .09) to increasing urea, with the lowest values observed at the highest urea level. As a result, digestible OM intake (DOMI) declined (linear, P = .03) with increasing proportions of urea and tended (quadratic, P = .14) to exhibit the largest proportional decline at the highest urea level. The effects of increasing urea on duodenal N flow, microbial efficiency, ruminal contents, and fluid dilution rate were minimal. Ruminal ammonia N and molar percent acetate increased linearly (P < or = .02), whereas most other VFA (except propionate) decreased (P < or = .05) with increasing urea. In conclusion, although forage OM intake was not altered, OM digestion, NDF digestion, and DOMI were lowest when all supplemental DIP was supplied as urea. Changes in fermentation characteristics reflected the change in source of available nitrogen.

Ammonia↗
PubMed1977

Influence of nitrate and molybdenum on sulfur utilization by rumen microorganisms.

Twenty-four hours in vitro incubations were used to study the effect of nitrate and molybdenum on sulfur utilization by rumen microorganisms. Sulfur was added as sodium sulfate or sulfide at .1, .2, .3, or .4% of the substrate dry matter. Cellulose digestion was an indicator of microbial growth. The addition of .1 to .4% sulfate or sulfide sulfur increased cellulose digestion over the conrol, the two sulfur sources being equal in promoting cellulose digestion. No differences in cellulose digestion were found between .1 and .4% added sulfur. However, the addition of .4 of .8% nitrate-nitrogen depressed cellulose digestion and increased the requirement for both sulfate and sulfide. Depression was greater with .8% nitrate-nitrogen. In the presence of nitrate, sulfide was superior to sulfate in promoting cellulose digestion. When 4 or 8 ppm molybdenum were added to the incubations, increasing concentrations of both sulfate and sulfide were required to obtain maximum cellulose digestion. Molybdenum additions increased both the sulfate and sulfide requirement for maximum cellulose digestion.

Animals↗