Maintenance Energy Coefficient Research Articles

Influence of low-level tannin supplementation on comparative growth performance of Holstein and Angus × Holstein cross calf-fed concentrate-based finishing diets for 328 d.

The objective of the current study was to evaluate the effects of tannin and monensin supplementation in feedlot diets and breed (Holstein vs. Angus × Holstein) on growth performance, energetic efficiency, and carcass characteristics. Eighty purebred Holstein calves (HOL; initial body weight (BW) = 130 ± 5kg) and 80 Angus × Holstein calves (AXH; initial BW = 129 ± 6kg) were blocked by initial BW and randomly assigned to 40 pens. Dietary treatments consisted of a steam-flaked corn-based diet supplemented with (1) no feed additive (CON); (2) 30mg of monensin/kg of dry matter (DM; MON; Rumensin 90, Elanco, Greenfield, IN); (3) 1.5g tannin)/kg of DM (TAN; ByPro, 70% condensed tannin, SilvaFeed, Indunor, S.A., Buenos Aires, Argentina); (4) M + T, the combination of MON plus TAN dietary treatments. Data were analyzed as a randomized complete block in a 2 × 4 factorial arrangement of treatments, using pens as experimental units. There were no interactions (P > 0.05) between feed additives and breed. Supplemental MON increased (P ≤ 0.04) initial 112-d BW and gain efficiency. However, there were no dietary treatment effects (P > 0.10) on overall growth performance. Monensin supplementation decreased (P = 0.04) minimum daily ruminal temperature compared with other dietary treatments during July, but TAN did not affect ruminal temperature. Holstein steers had greater (P = 0.04) overall DM intake compared with AXH, with no difference (P = 0.19) in overall ADG, leading to increased (P < 0.01) gain efficiency for AXH compared with HOL. Dietary net energy for maintenance and gain, based on growth performance, were greater (P ≤ 0.01) for AXH vs HOL. Compared with HOL, AXH steers had greater (P ≤ 0.01) carcass weight, dressing percentage, kidney, pelvic, and heart fat, 12th rib fat thickness, longissimus area, and preliminary yield grade. Holstein steers had lower (P ≤ 0.04) minimum average ruminal temperature during June compared with AXH, with no differences (P ≥ 0.14) between breeds during July or August. Results indicate that feed additives did not appreciably affect steer growth performance and carcass characteristics, but crossbred AXH steers had greater growth performance, efficiency of dietary energy utilization, and carcass quality measures compared with HOL. This study observed a reduction (4.7%) in maintenance energy expenditure in AXH compared with HOL, implying in maintenance energy coefficient of 0.086 vs 0.082 for HOL and AXH, respectively.

Continuous Ethanol Production from D-xylose: Using Free Cells of Clavispora opuntiae

The continuous fermentation of D-xylose to ethanol by free cells of Clavispora opuntiae was studied in a continuous stirred tank reactor at 25 ± 0.5°C and pH 4.2 ± 0.2. The maximum 89.8 ± 0.04% ethanol yield was obtained as compared to theoretical yield and about 96.00 ± 0.05% sugar was utilized at a dilution rate of 0.014 h–1. The maximum values of volumetric ethanol (Qp) and biomass (Qx) productivity were found to be 0.67 ± 0.04 gp l–1 h–1 and 0.18 ± 0.007 gx l–1 h–1, respectively, at a dilution rate of 0.09 h–1. The maintenance energy coefficient for C. opuntiae was found to be 0.21 ± 0.005 gs gx–1 h–1, whereas the values of specific ethanol production rate (qp) and specific sugar uptake rate (qs) were found to increase almost linearly with the increase of dilution rate. The maximum specific ethanol productivity (qp max) and maximum specific sugar uptake rate (qs max) were 0.50 ± 0.004 gp gx–1 h–1 and 4.00 ± 0.006 gs gx–1 h–1, respectively.

Biodegradation dynamics and cell maintenance for the treatment of resorcinol and p-cresol by filamentous fungus Gliomastix indicus

Biodegradation of resorcinol and p-cresol using fungus Gliomastix indicus MTCC 3869 was investigated in batch culture experiments at 28 °C temperature and pH of 6 in the medium up to the initial concentration of 1300 mg/L and 700 mg/L for resorcinol and p-cresol, respectively. Five specific growth kinetic models and five specific degradation rate models were fitted to the experimental data in order to get best fitted kinetic models. The variation of observed growth yield and maintenance energy requirement with the initial substrate concentration was also studied. The model for maintenance energy coefficient was fitted to the experimental data. The model parameters were: m 1 = 0.0135 h −1, k = 0.054, μ max = 0.132 h −1 for resorcinol and m 1 = 0.0229 h −1, k = 0.011, μ max = 0.102 h −1 for p-cresol. Two mathematical models comprising of two sets of ODE were solved simultaneously to get degradation profiles with time. The model with varying growth yield and maintenance energy was found to be most appropriate biodegradation model.

Maintenance metabolism and carbon fluxes in Bacillus species

BackgroundSelection of an appropriate host organism is crucial for the economic success of biotechnological processes. A generally important selection criterion is a low maintenance energy metabolism to reduce non-productive consumption of substrate. We here investigated, whether various bacilli that are closely related to Bacillus subtilis are potential riboflavin production hosts with low maintenance metabolism.ResultsWhile B. subtilis exhibited indeed the highest maintenance energy coefficient, B. licheniformis and B. amyloliquefaciens exhibited only statistically insignificantly reduced maintenance metabolism. Both B. pumilus and B. subtilis (natto) exhibited irregular growth patterns under glucose limitation such that the maintenance metabolism could not be determined. The sole exception with significantly reduced maintenance energy requirements was the B. licheniformis strain T380B. The frequently used spo0A mutation significantly increased the maintenance metabolism of B. subtilis.At the level of 13C-detected intracellular fluxes, all investigated bacilli exhibited a significant flux through the pentose phosphate pathway, a prerequisite for efficient riboflavin production. Different from all other species, B. subtilis featured high respiratory tricarboxylic acid cycle fluxes in batch and chemostat cultures. In particular under glucose-limited conditions, this led to significant excess formation of NADPH of B. subtilis, while anabolic consumption was rather balanced with catabolic NADPH formation in the other bacilli.ConclusionDespite its successful commercial production of riboflavin, B. subtilis does not seem to be the optimal cell factory from a bioenergetic point of view. The best choice of the investigated strains is the sporulation-deficient B. licheniformis T380B strain. Beside a low maintenance energy coefficient, this strain grows robustly under different conditions and exhibits only moderate acetate overflow, hence making it a promising production host for biochemicals and riboflavin in particular.

Biodegradation kinetic studies for the removal of p-cresol from wastewater using Gliomastix indicus MTCC 3869

Biodegradation of p-cresol by a pure culture of new filamentous fungal strain Gliomastix indicus was studied. The fungus strain was acclimatized to the higher concentration of 700 mg/l of p-cresol in modified czapeck medium over a period of two months. The lag period was 24 h. The shake flask batch experiments were carried out at temperature of 28 °C and pH of 6 over a wide range of initial p-cresol concentration (10–700 mg/l) keeping initial biomass concentration constant at 18.72 mg/l. Experimentally it was observed that p-cresol was inhibitory type substrate and the inhibition effect of p-cresol became predominant above a concentration of 50 mg/l. The kinetics of cell growth and p-cresol degradation were investigated. Six kinetic models (Haldane, Andrews, Webb, Yano, Aiba, and Teissier) were fitted to the experimental growth kinetic data. Models by Haldane, Andrews, Webb and Yano (correlation coefficient R 2 > 0.99) were found to be most suitable models. In addition, the variation of observed yield coefficient Y X with specific growth rate μ g was investigated. The maintenance energy coefficient and true growth yield coefficient, were found to be 0.0227 h −1 and 1.0708 (mg/mg), respectively. The specific substrate utilization rate was represented in terms of specific biomass growth rate. The decay coefficient was found to be 0.0055 h −1. The effect of pH and nitrogen source of medium on biodegradation of p-cresol was investigated as well.

Mannitol relieves substrate inhibition during glucose fermentation by &lt;italic&gt;L. delbrucekii&lt;/italic&gt; due to shift in NADH/NAD&lt;sup&gt;+&lt;/sup&gt; ratio

Co-fermentation kinetics of glucose and mannitol with Lactobacillus delbrueckii NCIM 2025 has been studied in MRS media in aim to enhance lactic acid production. It was found that 0.05mole mannitol increases both cell mass and lactic acid yield significantly. Cell yield increases up to 0.2 hrs while total lactic acid concentration increases up to 22g/l. Mannitol in the medium also found to reduce the growth associated coefficient (α) from 8.3 to 6.3 and non-growth associated (maintenance energy) coefficient (β) from 0.3 to 0.07. Mannitol also reduces ethanol concentration up to 93g/l.

Analysis of Growth of Lactobacillus plantarum WCFS1 on a Complex Medium Using a Genome-scale Metabolic Model

A genome-scale metabolic model of the lactic acid bacterium Lactobacillus plantarum WCFS1 was constructed based on genomic content and experimental data. The complete model includes 721 genes, 643 reactions, and 531 metabolites. Different stoichiometric modeling techniques were used for interpretation of complex fermentation data, as L. plantarum is adapted to nutrient-rich environments and only grows in media supplemented with vitamins and amino acids. (i) Based on experimental input and output fluxes, maximal ATP production was estimated and related to growth rate. (ii) Optimization of ATP production further identified amino acid catabolic pathways that were not previously associated with free-energy metabolism. (iii) Genome-scale elementary flux mode analysis identified 28 potential futile cycles. (iv) Flux variability analysis supplemented the elementary mode analysis in identifying parallel pathways, e.g. pathways with identical end products but different co-factor usage. Strongly increased flexibility in the metabolic network was observed when strict coupling between catabolic ATP production and anabolic consumption was relaxed. These results illustrate how a genome-scale metabolic model and associated constraint-based modeling techniques can be used to analyze the physiology of growth on a complex medium rather than a minimal salts medium. However, optimization of biomass formation using the Flux Balance Analysis approach, reported to successfully predict growth rate and by product formation in Escherichia coli and Saccharomyces cerevisiae, predicted too high biomass yields that were incompatible with the observed lactate production. The reason is that this approach assumes optimal efficiency of substrate to biomass conversion, and can therefore not predict the metabolically inefficient lactate formation.

Effect of malic acid on the growth kinetics of Lactobacillus plantarum.

The fermentation kinetics of Lactobacillus plantarum were studied in a specially designed broth formulated from commercially available, dehydrated components (yeast extract, trypticase, ammonium sulfate) in batch and continuous culture. During batch growth in the absence of malic acid, the specific growth rate was 0.20 h(-1). Malic acid in the medium, at 2 mM or 10 mM, increased the specific growth rate of L. plantarum to 0.34 h(-1). An increase in the maximum cell yield due to malic acid also was observed. Malic acid in the medium (12 mM) reduced the non-growth-associated (maintenance energy) coefficient and increased the biomass yield in continuous culture, based on calculations from the Luedeking and Piret model. The biomass yield coefficient was estimated as 27.4 mg or 34.3 mg cells mmol(-1) hexose in the absence or presence of malic acid, respectively. The maintenance coefficient was estimated as 3.5 mmol or 1.5 mmol hexose mg(-1) cell h(-1) in the absence or presence of malic acid. These results clearly demonstrate the energy-sparing effect of malic acid on the growth- and non-growth-associated energy requirements for L. plantarum. The quantitative energy-sparing effect of malic acid on L. plantarum has heretofore not been reported, to our knowledge.

Bioenergetics of the alkaliphilic sulfate-reducing bacterium Desulfonatronovibrio hydrogenovorans.

Energy metabolism of the alkaliphilic sulfate-reducing bacterium Desulfonatronovibrio hydrogenovorans strain Z-7935 was investigated in continuous culture and in physiological experiments on washed cells. When grown in chemostats with H2 as electron donor, the cells had extrapolated growth yields [Y(max), g dry cell mass (mol electron acceptor)(-1)] of 5.5 with sulfate and 12.8 with thiosulfate. The maintenance energy coefficients were 1.9 and 1.3 mmol (g dry mass)(-1) x h(-1), and the minimum doubling times were 27 and 20 h with sulfate and thiosulfate, respectively. Cell suspensions reduced sulfate, thiosulfate, sulfite, elemental sulfur and molecular oxygen in the presence of H2. In the absence of H2, sulfite, thiosulfate and sulfur were dismutated to sulfide and sulfate. Sulfate and sulfite were only reduced in the presence of sodium ions, whereas sulfur was reduced also in the absence of Na+. Plasmolysis experiments showed that sulfate entered the cells via an electroneutral symport with Na+ ions. The presence of an electrogenic Na+-H+ antiporter was demonstrated in experiments applying monensin (an artificial electroneutral Na+-H+ antiporter) and propylbenzylylcholine mustard.HCl (a specific inhibitor of Na+-H+ antiporters). Sulfate reduction was sensitive to uncouplers (protonophores), whereas sulfite reduction was not affected. Changes in pH upon lysis of washed cells with butanol indicated that the intracellular pH was lower than the optimum pH for growth (pH 9.5). Pulses of NaCl (0.52 M) to cells incubated in the absence of Na+ did not result in ATP formation, whereas HCl pulses (shifting the pH from 9.2 to 7.0) did. Small oxygen pulses, which were reduced within a few seconds, caused a transient alkalinization. The results of preliminary experiments with chemiosmotic inhibitors provided further evidence that the alkalinization was caused by sodium--proton antiport following a primary electron-transport-driven sodium ion translocation. It is concluded that energy conservation in D. hydrogenovorans depends on a proton-translocating ATPase, whereas electron transport appears to be coupled to sodium ion translocation.

Continuous ethanol production from pineapple cannery waste

The continuous ethanol production from pineapple cannery waste by the respiration deficient strain Saccharomyces cerevisiae ATCC 24553 has been studied at 30°C and pH 4.5. Maximum ethanol yield (92.5% of the theoretical) was obtained at a dilution rate of 0.05 h −1. The maximum values for volumetric ethanol and biomass productivities were 3.75 g p l −1 h −1 and 0.63 g x l −1 h −1, respectively, at a dilution rate of 0.15 h −1. The maintenance energy coefficient for S. cerevisiae ATCC 24553 was found to be 1.12 g s g x −1 h −1. The maximum specific ethanol productivity and specific sugar uptake rate were found to be (0.98 g p g x −1 h −1 ) and (2.54 g s g x −1 h −1), respectively.

The effect of maintenance energy requirements on biomass production during wastewater treatment

The recognition that microorganisms satisfy their maintenance energy requirements in preference to producing additional biomass has revealed possible methods to reducing the generation of excess biomass during wastewater treatment. A relationship describing substrate utilization for maintenance and biomass production in substrate-limited continuous microbial cultures is presented. In continuously-fed, substrate-limited, microbial populations, it is proposed that the biomass production decreases proportionally to biomass concentration. To evaluate the significance of biomass concentration on biomass production, a laboratory chemostat containing Pseudomonas putida grown aerobically was fitted with a second stage in which the biomass in the reactor effluent was concentrated and a portion was recycled to enhance the biomass concentration. Overall substrate removal efficiency remained constant at each of the various biomass concentrations investigated. Increasing biomass concentration from 3 to 6 g l −1 reduced biomass production by 12% and analysis of a similar system observed that increasing biomass concentration from 1.7 g l −1 to 10.3 g l −1 reduced biomass production by 44%. Maintenance energy coefficients and true growth yields for operation both as a chemostat and with biomass recycle were found to be similar; q m=0.027±0.004 g substrate g biomass −1 h −1 and Y G=0.359±0.003 g biomass g substrate −1 and q m=0.021±0.008 g substrate g biomass −1 h −1 and Y G=0.385±0.022 g biomass g substrate −1, respectively. The relevance of these findings for biomass production in wastewater processes are discussed.

Fermentation Performance Characteristics of a Prehydrolyzate-Adapted Xylose-Fermenting Recombinant Zymomonas in Batch and Continuous Fermentations

Long-term (149 d) continuous fermentation was used to adapt a xylose-fermenting recombinant Zymomonas mobilis, strain 39676:pZB 4L, to conditioned (overlimed) dilute-acid yellow poplar hemicellulose hydrolyzate (“prehydrolyzate”). An “adapted” variant was isolated from a chemostat operating at a dilution rate of 0.03/h with a 50% (v/v) prehydrolyzate, corn steep liquor, and sugar-supplemented medium, at pH 5.75. The level of xylose and glucose in the medium was kept constant at 4% (w/v) and 0.8% (w/v), respectively. These sugar concentrations reflect the composition of the undiluted hardwood prehydrolyzate. The level of conditioned hardwood prehydrolyzate added to the medium was increased in 5% increments startingata level of 10%. At the upper level of 50% prehydrolyzate, the acetic-acid concentration was about 0.75% (w/v). The adapted variant exhibited improved xylose-fermentation performance in a pure-sugar, synthetic hardwood prehydrolyzate medium containing 4% xylose (w/v), 0.8% (w/v) glucose, and acetic acid in the range 0.4–1.0% (w/v). The ethanol yield was 0.48–0.50 g/g; equivalent to a sugar-to-ethanol conversion efficiency of 94–96% of theoretical maximum. The maximum growth yield and maintenance energy coefficients were 0.033 g dry cell mass (DCM)/g sugars and 0.41 g sugars/g DCM/h, respectively. The results confirm that long-term continuous adaptation is a useful technique for effecting strain improvement with respect to the fermentation of recalcitrant feedstocks.

A mutant of Zymomonas mobilis ZM4 capable of ethanol production from glucose in the presence of high acetate concentrations.

Growth of Zymomonas mobilis ZM4 in media containing sodium acetate was inhibited above 12 g sodium acetate/l at pH 5.0. Following mutagenesis of ZM4, an acetate-tolerant strain was isolated in continuous culture that grew in the presence of 20 g sodium acetate/l at pH 5.0. In continuous culture with complete cell recycle at 30 deg C and pH 5.4 using media containing 110 g glucose/l, the maintenance energy coefficient (m) for the mutant was found to increase from 1.9 g glucose/g cell dry wt.h at 12 g sodium acetate/l up to 3.9 g/g.h at 20 g/l.

Relationship between substrate inhibition and maintenance energy ofChlamydomonas reinhardtii in heterotrophic culture

The relationship between substrate inhibition and maintenance energy ofChlamydomonas reinhardtii grown heterotrophically on acetate was investigated. At low acetate concentrations ( 0.4 g l−1), inhibition of cell growth occurred, in which m became variable and dependent on the acetate concentration. A simple mathematical model was proposed to predict the actual maintenance energy coefficient m in the inhibited cultures and experimentally validated.

Metabolic burden as reflected by maintenance coefficient of recombinant Escherichia coli overexpressing target gene

Metabolic burden as a consequence of overexpression of target gene in a recombinant strain of E. coli 1727 has been analyzed with respect to maintenance energy coefficient (m). The values of ‘m’ for the host, uninduced recombinant and IPTG induced recombinant were determined to be 0.12, 0.17 and 0.32 g.g-1.h-1 respectively. Transient plasmid instability and nearly 33% fall in maximum specific growth rate were observed under conditions of enhanced requirements for maintenance energy.

Xylose and arabinose utilization by the rumen bacterium Butyrivibrio fibrisolvens.

The rumen bacterium Butyrivibrio fibrisolvens strain D1 co-utilized xylose and glucose in batch culture, but there was a marked preference for glucose over arabinose. When both pentoses were provided, xylose was preferred over arabinose. Strain D1 co-utilized a combination of either pentose and cellobiose, but preferred over maltose. Pentose sugars were depleted less rapidly in the presence of sucrose than controls containing only pentose. In contrast, B. fibrisolvens strain A38 exhibited a strong preference for disaccharides, including maltose, over either xylose or arabinose. Theoretical maximum growth yields for strain D1 in single-substrate continuous culture were highest for sucrose and cellobiose and the maintenance energy coefficient for arabinose was at least 3.8-fold greater than for other substrates. We suggest that B. fibrisolvens may have evolved a mechanism to utilize certain sugars before arabinose in order to avoid this high maintenance energy expenditure.

Xylose and arabinose utilization by the rumen bacterium Butyrivibrio fibrisolvens

The rumen bacterium Butyrivibrio fibrisolvens strain D1 co-utilized xylose and glucose in batch culture, but there was a marked preference for glucose over arabinose. When both pentoses were provided, xylose was preferred over arabinose. Strain D1 co-utilized a combination of either pentose and cellobiose, but preferred pentoses over maltose. Pentose sugars were depleted less rapidly in the presence of sucrose than controls containing only pentose. In contrast, B. fibrisolvens strain A38 exhibited a strong preference for disaccharides, including maltose, over either xylose or arabinose. Theoretical maximum growth yields for strain D1v in single-substrate continuous culture were highest for sucrose and cellobiose and the maintenance energy coefficient for arabinose was at least 3.8-fold greater than for other substrates. We suggest that B. fibrisolvens may have evolved a mechanism to utilize certain sugars before arabinose in order to avoid this high maintenance energy expenditure.

Pathways of ethanol production from sucrose by a mutant thermophilic Bacillus in continuous culture

A mutant (strain LLD-15) of Bacillus stearothermophilus strain LLD-R, that lacks l-lactate dehydrogenase activity was studied in anaerobic single-stage continuous culture using a defined minimal medium for its capacity to produce ethanol from sucrose at 70 °C. Cultures were stable at neutral pH, dilution rates below 0·25 h−1 and sucrose concentrations below 15 g l−1, producing mainly ethanol, CO2, formate and acetate plus a little succinate. The data obtained were used to estimate the maintenance energy coefficient at 70 °C and showed that the relative fluxes through the pyruvate-formate lyase (PFL) pathway and an anaerobic pyruvate dehydrogenase (PDH) pathway were about equal, though the later predominates at low dilution rates. At higher dilution rates or at acid pH, l-lactate became the major anaerobic product due to takeover by wild-type revertants. Reversion occurred only above a critical specific sucrose consumption rate of 4·2 g sucrose h−1 (g cells)−1 at pH 7, at which point pyruvate production was also seen. This can be attributed to saturation of the PFL pathway and PDH pathways by increasing glycolytic flux and consequent accumulation of intracellular pyruvate. The growth rate then declines, but a small population of revertant LLD-R cells would always be present in the bioreactor since the mutation in the l-lactate dehydrogenase gene has a significant reversion rate. These revertants have no selective advantage below the critical sugar uptake rate, but at higher rates they divert excess pyruvate to L-lactate, so their growth is unimpaired and they take over in the culture. At lower pH, growth restriction and reversion occur at low sucrose consumption rates due to difficulty in excreting acetic and formic acids against a pH gradient.

High CO2 partial pressure depresses productivity and bioenergetic growth yield of Chlorella pyrenoidosa culture

When low-CO2 grown Chlorella pyrenoidosa (YSK strain) cells were exposed to high CO2 partial pressures (pCO2), the specific growth rate (μ) declined exponentially reaching a steady state value in about 20 h. A short interruption (up to 1 h) by temporarily lowering the pCO2 did not prevent the continuous decline in μ when high pCO2 was restored. In chemostate studies, light-limited cultures were supplied with 2 to 90 kPa of CO2. The steady state biomass production rate and bioenergetic growth yield were related inversely to pCO2 and the average energy uptake rate. The maintenance energy coefficient was, however, independent of dissolved pCO2 in the pCO2 range studied.

Membrane bioreactors for the evaluation of maintenance phenomena in wastewater treatment

A membrane bioreactor was used to calculate the maintenance coefficients m s, m o2; g · g −1 h −1) and theoretical maximum yields ( Y x/s, Y x/o2; g · g −1) of Pseudomonas fluorescens cultures taken as a model when grown on a limiting substrate complex medium, similar to a synthetic wastewater. The total control of the aerobic process of wastewater treatment in this type of reactor, and the perspective of the reduction of sludge production were directly related to this purpose. The operating conditions were either a total cell recycle or various imposed breeding rates; similar values of growth constants were obtained. It was established that the substrate mass flow (fixed by the dilution rate, D s, independent of the breeding rate D b), had no influence on the values of m and Y. No deviation of the slope of the linear regressions serving to calculate these parameters was observed, even at low biomass breeding rates D b (<5% μ max). The concept of the maintenance energy coefficient and the advantages of this technical tool are discussed.