The Experts below are selected from a list of 77577 Experts worldwide ranked by ideXlab platform

Erdal Toprak - One of the best experts on this subject based on the ideXlab platform.

Roy Kishony - One of the best experts on this subject based on the ideXlab platform.

Olaf Wolkenhauer - One of the best experts on this subject based on the ideXlab platform.

  • a systems biology approach to investigate the effect of ph induced gene regulation on solvent production by clostridium acetobutylicum in Continuous Culture
    BMC Systems Biology, 2011
    Co-Authors: Sylvia Haus, Sara Jabbari, Thomas Millat, Holger Janssen, Ralf Jorg Fischer, Hubert Bahl, J R King, Olaf Wolkenhauer
    Abstract:

    Background: Clostridium acetobutylicum is an anaerobic bacterium which is known for its solvent-producing capabilities, namely regarding the bulk chemicals acetone and butanol, the latter being a highly efficient biofuel. For butanol production by C. acetobutylicum to be optimized and exploited on an industrial scale, the effect of pH-induced gene regulation on solvent production by C. acetobutylicum in Continuous Culture must be understood as fully as possible. Results: We present an ordinary differential equation model combining the metabolic network governing solvent production with regulation at the genetic level of the enzymes required for this process. Parameterizing the model with experimental data from Continuous Culture, we demonstrate the influence of pH upon fermentation products: at high pH (pH 5.7) acids are the dominant product while at low pH (pH 4.5) this switches to solvents. Through steady-state analyses of the model we focus our investigations on how alteration in gene expression of C. acetobutylicum could be exploited to increase butanol yield in a Continuous Culture fermentation. Conclusions: Incorporating gene regulation into the model of solvent production by C. acetobutylicum enables an accurate representation of the pH-induced switch to solvent production to be obtained and theoretical investigations of possible synthetic-biology approaches to be pursued. Steady-state analyses suggest that, to increase butanol yield, alterations in the expression of single solvent-associated genes are insufficient; a more complex approach targeting two or more genes is required.

M D Stern - One of the best experts on this subject based on the ideXlab platform.

  • evaluation of iso α acid and β acid extracts from hops humulus lupulus l on fermentation by rumen microbes in dual flow Continuous Culture fermenters
    Animal Feed Science and Technology, 2020
    Co-Authors: I J Salfer, Samuel W Fessenden, M D Stern
    Abstract:

    Abstract Hops (Humulus lupulus L.), primarily used in the brewing industry, have been shown to have bacteriostatic properties against Gram-positive bacteria. Active antimicrobial compounds contained within hop flowers include iso-α-acids (isohumulones) and β-acids (lupulones). Previous experiments have demonstrated effects of hop extracts on rumen fermentation in batch Culture. The objective of this study was to determine the direct effects of iso-α-acids and β-acids on rumen fermentation in Continuous Culture fermenters. Two experiments were conducted using dual-flow Continuous Culture fermenters. Each experiment utilized eight fermenters in two consecutive 10 d periods. Within both experiments, the same basal diet consisting of 44 % corn silage, 14 % alfalfa hay, 13 % ground corn, 11 % protein mix, 10 % corn gluten feed, 5 % cottonseed and 3 % liquid vitamin and mineral supplements on a DM basis was provided to the fermenters at a rate of 75 g of DM/L of fermenter volume/day. In experiment 1, hop beta-extract was added daily to the artificial saliva buffer to supply 0 (CON), 600 (LOW), 1200 (MED), or 1800 (HIGH) mg of β-acids/kg of diet DM/day. In experiment 2, hop iso-α extract was provided to fermenters via the artificial saliva buffer to supply 0 (CON), 600 (LOW), 1200 (MED), or 1800 (HIGH) mg of iso-α-acids/kg of diet DM/day. Data in both experiments were analyzed as a randomized complete block design with experimental period serving as a block and all treatments equally represented within each block. Data were statistically analyzed using GLM procedure of SAS with a model including the fixed effects of experimental period (block), treatment, and the interaction of treatment and period. In experiment 1, mean and maximum fermentation pH increased (P = 0.005) linearly with increasing levels of beta extract inclusion. Additionally, time spent below pH 5.8 increased and time between pH 5.8 and 6.2 decreased (P = 0.007) linearly with greater beta extract inclusion (P = 0.08). However, beta extract did not affect DM, OM, NDF or ADF digestion. Furthermore, beta extract did not modify VFA production or N metabolism. In experiment 2, iso-alpha extract also increased average pH, and tended to increase time above pH 6.2. Iso-α extract did not affect DM, OM, NDF and ADF digestion, VFA production, or N metabolism. Results indicate that increasing the concentration of beta extract or iso-α extract increase rumen pH within Continuous Culture, but neither extract affects rumen nutrient digestion.

  • comparison of warm season and cool season forages for dairy grazing systems in Continuous Culture
    Translational animal science, 2018
    Co-Authors: Kathryn E Ruh, I J Salfer, Bradley J Heins, Robert D Gardner, M D Stern
    Abstract:

    The objective of this study was to compare warm-season annual grasses to cool-season perennial (CSP) grasses for ruminal nutrient digestibility and N metabolism in a dual-flow Continuous Culture fermentation system. Dietary treatments were 1) fresh alfalfa, 2) CSP grasses and legumes, 3) brown-midrib sorghum-sudangrass (BMRSS), and 4) teff grass from an organic dairy production system. Eight dual-flow Continuous Culture fermenters were used during two consecutive 10-d periods consisting of 7 d for stabilization followed by 3 d of sampling. Fermenter samples were collected on days 8, 9, and 10 for analysis of pH, NH3-N, and VFA. Apparent DM, OM, NDF, and ADF digestibility were on average lesser (P 0.05) by forage. The NH3-N concentrations were highest (P 0.05) by forage treatment. Flow of NH3-N was greatest (P 0.05) by forage source. Overall, fermentation of warm-season grasses was similar to the cool-season grasses and legumes which indicate dairy producers may use warm-season grasses without concerns about negative impact on rumen health.

  • effects of two halophytic plants kochia and atriplex on digestibility fermentation and protein synthesis by ruminal microbes maintained in Continuous Culture
    Asian-australasian Journal of Animal Sciences, 2012
    Co-Authors: Atiye Riasi, Danesh M Mesgaran, M D Stern, Ruiz M Moreno
    Abstract:

    Eight Continuous Culture fermenters were used in a completely randomized design to evaluate various nutritional values of Kochia (Kochia scoparia) compared with Atriplex (Atriplex dimorphostegia). Dried and pelleted samples (leaves and stems) provided substrate for metabolism by ruminal microbes maintained in a Continuous Culture fermentation system. Results indicated that there were no differences (p>0.05) in dry matter (DM) and crude protein (CP) digestibility between the two halophytic plants. Atriplex had higher (p 0.05) between the two halophytic plants in molar proportion of acetate and propionate, but the concentration of butyrate and valerate in Kochia were about two fold of Atriplex (p<0.05). When Kochia provided substrate to the microbes, protein synthesis was higher (p<0.05) compared with feeding Atriplex (5.96 vs. 4.85 g N/kg of OM truly digested). It was concluded that Kochia scoparia and Atriplex dimorphostegia had similar digestibility of DM and CP. It appears that these halophytic plants may not have enough digestible energy for high producing ruminants.

  • effects of patulin on rumen microbial fermentation in Continuous Culture fermenters
    Animal Feed Science and Technology, 2002
    Co-Authors: M O Tapia, M D Stern, R L Koski, A. Bach, M J Murphy
    Abstract:

    Eight single-flow Continuous Culture fermenters were used to study the effects of different concentrations of patulin on rumen microbial fermentation. Two 11 fermenters were spiked with 0, 30, 60 or 90 mg of patulin every 12 h for 3 consecutive days. True digestion of organic matter (TOM), acid detergent fiber (ADF) and crude protein (CP) decreased (P 0.05) between the control treatment and 30-60 mg of patulin. Acetate (mol/100 mol) was depressed (P < 0.01) with patulin addition. Conversely, there was an increase (P < 0.05) in the molar proportion of butyrate and valerate in the fermenters treated with the toxin. At the highest level of patulin addition (60 and 90 mg), branched-chain VFA were lower (P < 0.01) probably due to a reduction in protein (branched-chain amino acid) degradation. It is concluded that patulin can alter metabolism of nutrients by ruminal microbes. These changes could potentially have a negative impact on animal health and performance.

  • effects of extruded soybeans and forage source on fermentation by rumen microorganisms in Continuous Culture
    Journal of Dairy Science, 1994
    Co-Authors: D.j. Illg, M D Stern, H.r. Mansfield, Brian A Crooker
    Abstract:

    Abstract Continuous Culture fermenters were used to evaluate effects of extrusion of whole soybeans and changes in forage composition of diets on microbial fermentation. Treatments were arranged in a 2 × 4 factorial design with soybeans (raw or extruded) and dietary treatment (ratio of alfalfa hay to corn silage; 82:18, 61:39, 43:57, and 27:73 of dietary forage) as main effects. Soybeans constituted 9.6, 14.4, 19.2, and 23.9% of DM for each of the respective dietary treatments. True digestion of DM, ADF, and NDF was unaffected by processing of soybeans or dietary treatment, but true digestion of OM decreased as concentration of corn silage and soybeans increased. Total VFA concentration was unaffected by source of soybeans or dietary treatments; however, molar concentration of butyrate decreased in fermenters supplied with diets containing extruded soybeans. Degradation of CP was not influenced by soybean source but decreased as the concentration of corn silage and soybeans increased. Bacterial N output decreased, and dietary N flow from the fermenters increased, as concentration of corn silage and soybeans increased. Changes in the ratio of alfalfa hay to corn silage and alteration of dietary soybean concentration affected true OM digestion and dietary CP degradation, but extrusion of whole soybeans had little effect on fermentation.

Jochen Petersen - One of the best experts on this subject based on the ideXlab platform.

  • the kinetics of ferrous iron oxidation by leptospirillum ferriphilum in Continuous Culture the effect of temperature
    Biochemical Engineering Journal, 2009
    Co-Authors: Tunde Victor Ojumu, G. S. Hansford, Jochen Petersen
    Abstract:

    Abstract A typical bioleach heap is characterized by wide variation of temperature across the heap bed, leading to oxidation of target minerals occurring at different rates. Previous studies on the effect of temperature on the microbial oxidation of ferrous-iron were limited to a narrow range of temperatures (30–40 °C) near optimum conditions and mostly to Acidithiobacillus ferrooxidans . The kinetics of ferrous-iron oxidation by Leptospirillum ferriphilum were studied in Continuous Culture. In this paper we focus on the effect of temperature (18–45 °C) on these kinetics. The study was based on the assumption that the effect of temperature can be studied independently of other, equally important factors such as pH, dissolved salts, etc. and independent of the reactor context. The experimental data were correlated using both, a simplified ferric-iron inhibitory model and the Pirt Equation. The results showed that the maximum specific ferrous-iron oxidation rate, q F e 2 + max increased with increasing temperature to a maximum at 42 °C. This trend can be described adequately by the Arrhenius Equation with an activation energy, E a of 34.46 kJ mol −1 and frequency factor, K 0 of 1.05 × 10 7  mmol Fe 2+ (mmolC) −1  h −1 . An increase in temperature slightly reduces the steady state carbon biomass in the reactor, while the apparent affinity constant, K ′ F e 2 + increases. The investigation further suggests that at low temperature (18 °C) and beyond the maximum temperature (42 °C), the Culture cannot be sustained in a Continuous mode. The maximum biomass yield followed a linear decline with increasing temperature, while cell maintenance on ferrous-iron followed a quadratic trend, although the small values indicates that it is not significant, as would be expected in Continuous Culture. The results indicate that L. ferriphilum is likely to perform optimally, at warm temperatures (25–42 °C) in heap bioleach operations before being taken over by thermophiles at higher temperatures.

  • the effect of dissolved cations on microbial ferrous iron oxidation by leptospirillum ferriphilum in Continuous Culture
    Hydrometallurgy, 2008
    Co-Authors: Tunde Victor Ojumu, Jochen Petersen, G. S. Hansford
    Abstract:

    Abstract In heap bioleaching the dissolution of gangue minerals from igneous ore materials can lead to the build-up of considerable concentrations of Mg and Al sulphates in the recycled leach solution. This may interfere with microbial ferrous iron oxidation, which drives the oxidation of the target minerals. In the present study the effect of solution concentrations of Mg and Al as sulphate at individual concentrations of 0 to 10 g·dm − 3 and combined concentrations 0 to 16 g·dm − 3 each (or total ionic strength from 0.2 to 1.3 M) has been investigated in Continuous Culture using Leptospirillum ferriphilum . Increasing the concentrations of the salts increasingly depresses the specific rate of ferrous iron oxidation and also shifts the viable range more and more into the low potential region. Aluminium significantly reduces the amount of carbon biomass maintained in the reactor, whereas magnesium actually enhances it at low concentrations. The experimental data was correlated using the Pirt equation and a simplified substrate utilisation model. The results suggest that the maximum microbial growth rate and growth yield decline significantly only at total ionic strengths above about 1 mol·dm −3 . The implications of this study are that heap Cultures are likely to perform sub-optimally in those operations where build-up of dissolved gangue minerals is not controlled.