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The planning of the maintenance process for physical assets has a great connotation due to the need to increase the use of installed productive capacities. The objective of this research was to analyze the calculation of the time fund and its relationship with the maintenance coefficient, as elements to be defined from the planning of the maintenance process to the assets, which contributes to the improvement of the effective capacity and continuity of operations of the means of work. The result provided a proposal for the practical application of the value of the maintenance coefficient, which was incorporated into the calculation of the process capabilities. The results were obtained from the application of techniques and tools proposed for the collection and processing of primary data such as: direct observation, interview, document analysis and others. [ABSTRACT FROM AUTHOR]

For biogas-producing continuous stirred tank reactors, an increase in dilution rate increases the methane production rate as long as substrate input can be converted fully. However, higher dilution rates necessitate higher specific microbial growth rates, which are assumed to have a strong impact on the apparent microbial biomass yield due to cellular maintenance. To test this, we operated two reactors at 37°C in parallel at dilution rates of 0.18 and 0.07 days-1 (hydraulic retention times of 5.5 and 14 days, doubling times of 3.9 and 9.9 days in steady state) with identical inoculum and a mixture of volatile fatty acids as sole carbon sources. We evaluated the performance of the Anaerobic Digestion Model No. 1 (ADM1), a thermodynamic black box approach (TBA), and dynamic flux balance analysis (dFBA), to describe the experimental observations. All models overestimated the impact of dilution rate on the apparent microbial biomass yield when using default parameter values. Based on our analysis, a maintenance coefficient value below 0.2 kJ per carbon mole of microbial biomass per hour should be used for the TBA, corresponding to 0.12 mmol ATP per gram dry weight per hour for dFBA, which strongly deviates from the value of 9.8 kJ Cmol h-1 that has been suggested to apply to all anaerobic microorganisms at 37°C. We hypothesized that a decrease in dilution rate might select taxa with minimized maintenance expenditure. However, no major differences in the dominating taxa between the reactors were observed based on amplicon sequencing of 16S rRNA genes and terminal restriction fragment length polymorphism analysis of mcrA genes. Surprisingly, Methanosaeta dominated over Methanosarcina even at a dilution rate of 0.18 days-1, which contradicts previous model expectations. Furthermore, only 23–49% of the bacterial reads could be assigned to known syntrophic fatty acid oxidizers, indicating that unknown members of this functional group remain to be discovered. In conclusion, microbial maintenance was found to be much lower for acetogenesis and methanogenesis than previously assumed, likely due to the exceptionally low growth rates in anaerobic digestion. This finding might also be relevant for other microbial systems operating at similarly low growth rates.

Two randomized complete block design experiments were conducted to evaluate the effect of bedding use in confined beef steers. Experiment 1 used Simmental × Angus steers (n = 240; initial body weight (BW) = 365 ± 22.5 kg). Experiment 2 used newly weaned Charolais × Red Angus steers (n = 162; initial BW = 278 ± 13.4 kg). Steers were allotted to one of two treatments: (1) no bedding (NO), or (2) 1.8 kg (Experiment 1) or 1.0 kg (Experiment 2) of wheat straw (as-is basis) bedding/steer·d−1 (BED). In Experiment 1, applying bedding improved (p ≤ 0.01) dry matter intake (DMI), kg of gain to kg of feed (G:F), and average daily gain (ADG). Bedding reduced (p = 0.01) the estimated maintenance coefficient (MQ). Dressing percentage, rib fat, marbling, and yield grade were increased (p ≤ 0.03) in NO. Bedding resulted in an increase (p = 0.01) in serum insulin-like growth factor I (IGF-I). In Experiment 2, a tendency (p = 0.06) for increased DMI for NO was noted. Bedding improved G:F (p = 0.01). MQ was elevated (p = 0.03) for NO and NO had an increase (p = 0.02) in serum concentration of urea-N (SUN). An increase (p = 0.01) in serum non-esterified fatty acid was noted for NO. These data indicate that bedding application should be considered to improve growth performance and feed efficiency by reducing maintenance energy requirements in beef steers during the feedlot receiving and finishing phase.

Sludge reduction by physico-chemical methods results in the buildup of chemicals, which may require further treatment. Owing these reasons various biologically sustainable methods of sludge reduction including the application of high oxygenation have been successfully tested. Experiments on actual sewage in two lab-scale sequencing batch reactors (SBRs) were conducted under normal (1.5–2.5 mgDO/L) and high dissolved oxygen (DO) (HDO: 3–6.5 mgDO/L) regimes. It was observed that microorganism allocated substrate between maintenance and growth in the form of maintenance coefficient. Which could be induced by endogenous respiration owing to high solids retention time (SRT), predation on bacteria, chemical toxicity, adverse environment, and viral attack on bacteria. The wastewater treatment process may experience one or more maintenance inducing factors; nevertheless, high SRT and prevailing environmental conditions are imminent and thus considered as primary maintenance (m p ), while remaining are classified as secondary maintenance (m s ). Average yield coefficient reduction at HDO was 32.7% and 28.2% compared to stoichiometric and at normal DO, respectively. The observed primary and secondary maintenance was 0.11gCOD/gVSS.d (±0.01) at an SRT of 25.2 d (±2.0) and 0.096 g 0.1 gCOD/gVSS.d (±0.045) at an SRT of 24.2 d (±3.6d), respectively. The results obtained under the study are not as precise as on pure culture and defined substrate, nevertheless, it gives an idea that how stress factors inducing maintenance need to be addressed more seriously and objectively while managing our efforts on sludge reduction. [ABSTRACT FROM AUTHOR]

ABSTRACT Acidithiobacillus ferrooxidans is an acidophilic chemolithoautotroph that is important in biomining and other biotechnological operations. The cells are able to oxidize inorganic iron, but the insolubility and product inhibition by Fe3+ complicates characterization of these cultures. Here we explore the growth kinetics of A. ferrooxidans in iron-based medium in a pH range from 1.6 to 2.2. It was found that as the pH was increased from 1.6 to 2.0, the maintenance coefficient decreased while both the growth kinetics and maximum cell yield increased in the precipitate-free, low Fe2+ concentration medium. In higher iron media a similar trend was observed at low pH, but the formation of precipitates at higher pH (2.0) hampered cell growth and lowered the specific growth rate and maximum cell yield. In order to eliminate ferric precipitates, chelating agents were introduced into the medium. Citric acid was found to be relatively non-toxic and did not appear to interfere with iron oxidation at a maximum concentration of 70 mM. Inclusion of citric acid prevented precipitation and A. ferrooxidans growth parameters resumed their trends as a function of pH. The addition of citrate also decreased the apparent substrate saturation constant ( KS) indicating a reduction in the competitive inhibition of growth by ferric ions. These results indicate that continuous cultures of A. ferrooxidans in the presence of citrate at elevated pH will enable enhanced cell yields and productivities. This will be critical as these cells are used in the development of new biotechnological applications such as electrofuel production. Biotechnol. Bioeng. 2014;111: 1940-1948. © 2014 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: In this study a comparative analysis of three Corynebacterium glutamicum ATCC 13032 respiratory chain mutants lacking either the cytochrome bd branch (ΔcydAB), or the cytochrome bc 1–aa 3 branch (Δqcr), or both branches was performed. The lack of cytochrome bd oxidase was inhibitory only under conditions of oxygen limitation, whereas the absence of a functional cytochrome bc 1–aa 3 supercomplex led to decreases in growth rate, biomass yield, respiration and proton-motive force (pmf) and a strongly increased maintenance coefficient under oxygen excess. These results show that the bc 1–aa 3 supercomplex is of major importance for aerobic respiration. For the first time, a C. glutamicum strain with a completely inactivated aerobic respiratory chain was obtained (ΔcydABΔqcr), named DOOR (devoid of oxygen respiration), which was able to grow aerobically in BHI (brain–heart infusion) glucose complex medium with a 70% reduced biomass yield compared to the wild type. Surprisingly, reasonable aerobic growth was also possible in glucose minimal medium after supplementation with peptone. Under these conditions, the DOOR strain displayed a fermentative type of catabolism with l-lactate as major and acetate and succinate as minor products. The DOOR strain had about 2% of the oxygen consumption rate of the wild type, showing the absence of additional terminal oxidases. The pmf of the DOOR mutant was reduced by about 30% compared to the wild type. Candidates for pmf generation in the DOOR strain are succinate:menaquinone oxidoreductase, which probably can generate pmf in the direction of fumarate reduction, and F1FO-ATP synthase, which can couple ATP hydrolysis to the export of protons. [Copyright &y& Elsevier]

We attempted to reconcile three microbial maintenance models ( Herbert, Pirt, and Compromise) through a theoretical reassessment. We provided a rigorous proof that the true growth yield coefficient ( Y G) is the ratio of the specific maintenance rate ( a in Herbert) to the maintenance coefficient ( m in Pirt). Other findings from this study include: (1) the Compromise model is identical to the Herbert for computing microbial growth and substrate consumption, but it expresses the dependence of maintenance on both microbial biomass and substrate; (2) the maximum specific growth rate in the Herbert ( μmax, H) is higher than those in the other two models ( μmax, P and μmax, C), and the difference is the physiological maintenance factor ( m q = a); and (3) the overall maintenance coefficient ( m T) is more sensitive to m q than to the specific growth rate ( μ G) and Y G. Our critical reassessment of microbial maintenance provides a new approach for quantifying some important components in soil microbial ecology models. [ABSTRACT FROM AUTHOR]

A respirometric approach has been developed to determine heterotrophic biofilm kinetics using fluidized bioparticles – particles with attached biomass. Lava rock particles of 600 μ m were used as a biomass carrier medium. The modified respirometer successfully estimates in situ biofilm kinetics of the bioparticles collected from a pilot-scale liquid–solid circulating fluidized bed (LSCFB) bioreactor. The observed maximum specific growth rates (μmax) of 3.69±0.44 d−1 and biomass yields (Y H ) of 0.36±0.03 g COD/g COD in the fluidized bed respirometers were significantly different from the μmax of 5.57–5.72 d−1 and Y H of 0.54–0.59 g COD/g COD observed in the conventional respirometric tests for bioparticles and detached biomass. The higher Monod half-saturation coefficient (K S ) of 186–219 mg COD/L observed in the fluidized bed respirometers relative to the 49–58 mg COD/L in the conventional respirometers reveals the presence of mass transfer resistance in the LSCFB despite fluidization. Significantly reduced yields in the fluidized bed respirometers and the estimated maintenance coefficient of 1.16 d−1 for the particulate biofilm in the LSCFB clearly emphasize that a substantial amount of substrate was utilized for cell maintenance at the low food to microorganism (S/X) ratio of 0.5 g COD/g VSS. [ABSTRACT FROM PUBLISHER]

Abstract: Solid-state fermentation (SSF) is defined as the growth of microbes without a free-flowing aqueous phase. The feasibility of using a citrus peel for producing pectinase and xylanase via the SSF process by Aspergillus niger F3 was evaluated in a 2kg bioreactor. Different aeration conditions were tested to optimize the pectinase and xylanase production. The best air flow intensity was 1VkgM (volumetric air flow per kilogram of medium), which allowed a sufficient amount of O2 for the microorganism growth producing 265U/g and 65U/g pectinases and xylanases, respectively. A mathematical model was applied to determine the different kinetic parameters related to SSF. The specific growth rate and biomass oxygen yield decreased during fermentation, whereas an increase in the maintenance coefficient for the different employed carbon sources was concurrently observed. [Copyright &y& Elsevier]

One of the key roles of an organic solvent has emerged to be the enhancement of oxygen transfer in two-phase partitioning bioscrubbers (TPPBs). In order to determine an optimum organic fraction for a given VOCs loading, the oxygen demand of the total cell mass must be estimated, which depends upon the magnitude of the cellular maintenance coefficient. We have estimated the dynamics of the maintenance coefficient for benzene degradation by Achromobacter xylosoxidans Y234 in a TPPB and found that the maintenance coefficient generally decreased as cells accumulated in the TPPB but converged to a specific value of 1.750 × 10−2 h−1 at biological steady state. Due to its important influence on all of the essential design parameters of the TPPB system, including optimum organic fraction, aeration rate and agitation speed, the maintenance coefficient should be considered as a key biological determinant for microorganism selection, as well as in overall TPPB design. [ABSTRACT FROM AUTHOR]

This study examined the continuous cofermentation performance characteristics of a dilute-acid “prehydrolysate-adapted” recombinant Zymomonas 39676:pZB4L and builds on the pH-stat batch fermentations with this recombinant that we reported on last year. Substitution of yeast extract by 1% (w/v) corn steep liquor (CSL) (50% solids) and Mg (2 mM) did not alter the coferm entation performance. Using declared assumptions, the cost of using CSL and Mg was estimated to be 12.5c/gal of ethanol with a possibility of 50% cost reduction using fourfold less CSL with 0.1% diammonium phosphate. Because of competition for a common sugar transporter that exhibits a higher affinity for glucose, utilization of glucose was complete whereas xylose was always present in the chemostat effluent. The ethanol yield, based on sugar used, was 94% of theoretical maximum. Altering the sugar ratio of the synthetic dilute acid hardwood prehydrolysate did not appear to significantly change the pattern of xylose utilization. Using a criterion of 80% sugar utilization for determining the maximum dilution rate ( D max), changing the composition of the feed from 4% xylose to 3%, and simultaneously increasing the glucose from 0.8 to 1.8% shifted D max from 0.07 to 0.08/h. With equal amounts of both sugars (2.5%), D max was 0.07/h. By comparison to a similar investigation with rec Zm CP4:pZB5 with a 4% equal mixture of xylose and glucose, we observed that at pH 5.0, the D max was 0.064/h and shifted to 0.084/h at pH 5.75. At a level of 0.4% (w/v) acetic acid in the CSL-based medium with 3% xylose and 1.8% glucose at pH 5.75, the D max for the adapted recombinant shifted from 0.08 to 0.048/h, and the corresponding maximum volumetric ethanol productivity decreased 45%, from 1.52 to 0.84 g/(L·h). Under these conditions of continuous culture, linear regression of a Pirt plot of the specific rate of sugar utilization vs D showed that 4 g/L of acetic acid did not affect the maximum growth yield (0.030 g dry cell mass/g sugar), but did increase the maintenance coefficient twofold, from 0.46 to 1.0 g of sugar/(g of cell·h). [ABSTRACT FROM AUTHOR]

Recombinant Zymomonas mobilis CP4:pZB5 was grown with pH control in batch and continuous modes with either glucose or xylose as the sole carbon and energy source. In batch cultures in which the ratio of the final cell mass concentration to the amount of sugar in the medium was constant (i.e., under conditions that promote “coupled growth”), maximum specific rates of glucose and xylose consumption were 8.5 and 2.1 g/(g of cell...h), respectively; maximum specific rates of ethanol production for glucose and xylose were 4.1 and 1.0 g/(g of cell...h), respectively; and average growth yields from glucose and xylose were 0.055 and 0.034 g of dry cell mass (DCM)/g of sugar respectively. The corresponding value of YATP for glucose and xylose was 9.9 and 5.1 g of DCM/mol of ATP, respectively. YATP for the wild-type culture CP4 with glucose was 10.4g of DCM/mol of ATP. For single substratechem ostat cultures in which the growth rate was varied as the dilution rate ( D), the maximum or “true” growth yield (max Ya/s) was calculated from Pirt plots as the inverse of the slope of the best-fit linear regression for the specific sugar utilization rate as a function of D, and the “maintenance coefficient” ( m) was determined as the y-axis intercept. For xylose, values of max Y s/s and m were 0.0417g of DCM/g of xylose (YATP=6.25) and 0.04g of, xylose/(g of cell...h), respectively. However, with glucose there was an observed deviation from linearity, and the data in the Pirt plot was best fit with a second-order polynomial in D. At D>0.1/h, YATP=8.71 and m=2.05g of glu/(g of cell...h) whereas at D<0.1/h, YATP=4.9g of DCM/mol of ATP and m=0.04g of glu/(g of cell...h). This observation provides evidence to question the validity of the unstructured growth model and the assumption that Pirt's maintenance coefficient is a constant that is in dependent of the growth rate. Collectively, these observations with individual sugars and the values assign ed to various growth and fermentation parameters will be useful in the development of models to predict the behavior of rec Zm in mixed substrate fermentations of the type associated with biomass-to-ethanol processes. [ABSTRACT FROM AUTHOR]

The ethanol-oxidizing, proton-reducing Pelobacter acetylenicus was grown in chemostat cocultures with either Acetobacterium woodii, Methanobacterium bryantii, or Desulfovibrio desulfuricans. Y and m were determined from the total molar growth yields determined at growth (dilution) rates between 0.02 and 0.14 h. The individual growth yields of the partner organisms were determined from their numbers and cellular mass in the chemostat cocultures. The Gibbs free energy (ΔG=-16.3 kJ/mol ethanol) available to P. acetylenicus as well as its Y (1.7-2.2 g/mol ethanol) were almost constant in the different cocultures. P. acetylenicus shared 44-67% of the total biomass produced, whereas it shared only 19, 23, and 37% of the total Gibbs free energy (ΔG) available from ethanol oxidation coupled to sulfate reduction, methanogenesis, and homoacetogenesis, respectively. The residual 63-81% of the total available ΔG were shared by the H oxidizers which exhibited Y values being highest for A. woodii (6.6 g/mol acetate) > D. desulfuricans (3.8 g/mol sulfide) > M. bryantii (2.2 g/mol CH). The results are discussed with respect to ATP generation and coupling of catabolism with cell production. [ABSTRACT FROM AUTHOR]

Methanobacterium thermoautotrophicum was grown in continuous culture in a fermenter gassed with H and CO as sole carbon and energy sources, and in a medium which contained either NHCl or gaseous N as nitrogen source. Growth was possible with N. Steady states were obtained at various gas flow rates with NHCl and with $$N2{\text{ }} \cdot {\text{ Y}}_{{\text{CH}}{}_{\text{4}}} $$ and the maintenance coefficient varied with the gas input and with the nitrogen source. Growth of Methanococcus thermolithotrophicus in continuous culture in a fermenter gassed with H, CO as nitrogen, carbon and energy sources was also examined. [ABSTRACT FROM AUTHOR]

Methanococcus thermolithotrophicus was grown in a mineral salts medium at 65° C in a fermenter gassed with H and CO, which were the sole carbon and energy sources. Evolution of growth parameters during batch culture experiments showed the existence of an uncoupling phenomenon. The growth was then studied using a continuous technique and steady states for various gas flow rates were obtained. Yand the maintenance coefficient varied with the gas input. The maximum Y determined for Methanococcus thermolithotrophicus was 3.33 g·mol CH. An excess of energy and carbon sources induced uncoupling of growth. [ABSTRACT FROM AUTHOR]

Methanobacterium thermoautotrophicum was grown on a mineral salts medium in a fermenter gassed with H and CO, which were the sole carbon and energy sources. Under the conditions used the bacterium grew exponentially. The dependence of the growth rate (μ) on the concentration of H and CO in the incoming gas and the dependence of the growth yield ( $$Y_{CH_4 }$$ ) on the growth rate were determined at pH 7 (the pH optimum) and 65° C (the temperature optimum). The curves relating growth rate to the H and CO concentration were hyperbolic. From reciprocal plots apparent K values for H and CO and μ were obtained: app. $$K_{{\text{H}}_{\text{2}} }$$ = 20%; app. $$K_{{\text{CO}}_{\text{2}} }$$ = 11%; μ = 0.69 h; t (max)=1 h. $$Y_{CH_4 }$$ was 1.6 g mol and almost independent of the growth rate, when the rate of methane formation was not limited by the supply of either H or CO. The yield increased to near 3 g mol when H or CO were limiting. These findings indicate that methane formation and growth are less tightly coupled at high concentrations of H or CO in the medium than at low concentrations. The physiological significance of these findings is discussed. [ABSTRACT FROM AUTHOR]

Simple Summary: A sizeable portion of cattle fed in the United States are fed in the Upper Midwest and Northern Plains where winter temperatures routinely fall below freezing. Using bedding application to improve cattle comfort and performance has been a common practice in livestock production for many years. However, the exact degree to which bedding improves performance is difficult to quantify. As such, two studies were conducted to evaluate the effects of bedding use on growth performance, estimated maintenance energy requirement, carcass characteristics, sera responses in beef steers of differing ages, and phases of feedlot production. Experiment 1 showed that applying wheat straw bedding to yearling crossbred beef steers at a rate of 1.8 kg/steer·d−1 increased feed consumption, feed efficiency, and average daily gain. In experiment 2, newly weaned calves bedded with 1.0 kg of wheat straw bedding/steer·d−1 tended to consume 4.5% less feed and had a 5.6% improvement in feed efficiency. In both studies, the energy required for maintenance for non-bedded steers was increased. These experiments indicate that bedding application should be considered to improve growth performance and feed efficiency in beef steers by reducing maintenance energy requirements during the feedlot receiving and finishing phases. Two randomized complete block design experiments were conducted to evaluate the effect of bedding use in confined beef steers. Experiment 1 used Simmental × Angus steers (n = 240; initial body weight (BW) = 365 ± 22.5 kg). Experiment 2 used newly weaned Charolais × Red Angus steers (n = 162; initial BW = 278 ± 13.4 kg). Steers were allotted to one of two treatments: (1) no bedding (NO), or (2) 1.8 kg (Experiment 1) or 1.0 kg (Experiment 2) of wheat straw (as-is basis) bedding/steer·d−1 (BED). In Experiment 1, applying bedding improved (p ≤ 0.01) dry matter intake (DMI), kg of gain to kg of feed (G:F), and average daily gain (ADG). Bedding reduced (p = 0.01) the estimated maintenance coefficient (MQ). Dressing percentage, rib fat, marbling, and yield grade were increased (p ≤ 0.03) in NO. Bedding resulted in an increase (p = 0.01) in serum insulin-like growth factor I (IGF-I). In Experiment 2, a tendency (p = 0.06) for increased DMI for NO was noted. Bedding improved G:F (p = 0.01). MQ was elevated (p = 0.03) for NO and NO had an increase (p = 0.02) in serum concentration of urea-N (SUN). An increase (p = 0.01) in serum non-esterified fatty acid was noted for NO. These data indicate that bedding application should be considered to improve growth performance and feed efficiency by reducing maintenance energy requirements in beef steers during the feedlot receiving and finishing phase. [ABSTRACT FROM AUTHOR]

An abstract of the article "Energetic analysis of Pseudomonas flourescens growth in aerobic chemostat culture," by Samuel E. Agarry and Bamidele O. Solomon is presented.