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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study investigates the influence of fluctuating toluene concentrations on aerobic toluene degradation in a sandy porous medium colonized with Ralstonia pickettii PKO1. Column effluent toluene concentrations were found to increase after a temporary decrease in influent toluene concentration. Subsequent examination of the spatial gradient of toluene degradative activity in the column suggested that the observed increase in effluent toluene concentrations was attributable to an adverse effect of toluene limitation on the biodegradative activity of attached cells. The traditional Michaelis-Menten-type biodegradation equation associated with batch-measured Vmax (2.26 mg toluene/mg living cell/day) and KS (1.20 mg toluene/1) of nonstarved cells was unable to predict the observed toluene breakthrough behavior when the column had been previously exposed to no-toluene conditions. An alternative modeling approach was developed based upon the assumptions that (i) degradative activity was completely deactivated within the no-toluene exposure period (53.5 h) and (ii) a lag-phase was present prior to the subsequent reactivation of degradative activity in previously toluene-starved cells. These assumptions were independently verified by batch microbial investigations, and the modified model provided a good fit to the same observed toluene breakthrough curve. Application of single lag-time and threshold concentration values, however, failed to predict observed toluene breakthrough under different toluene exposure conditions. Results of this experimental and modeling investigation suggested that substrate exposure history, including the length of the starvation period and the level of substrate concentration, affected the induction of biodegradation in the porous medium.
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PMID:Influence of substrate exposure history on biodegradation in a porous medium. 1158 28

This study reports on the construction, calibration and use of recombinant cells of Rhodobacter capsulatus expressing the luciferase gene of the North American firefly Photinus pyralis to detect, by bioluminescence, variations of endogenous ATP levels under various physiological conditions. We show that the antibiotic polymyxin B allows luciferin to rapidly move into cell cytosol, but does not make external ATP freely accessible to intracellular luciferase. Notably, in toluene:ethanol-permeabilized cells, the apparent K(mATP) for luciferase (50 microM) is similar to that measured in soluble cell fractions. This finding limits the applicability of the firefly luciferase for monitoring intracellular maximal ATP concentration because dark/aerobic-grown recombinant cells of Rba. capsulatus contain approximately 1.3-2.6+/-0.5 mM ATP. Therefore, the effects of chemical and physical factors such as oxygen, light, carbonyl cyanide m-chlorophenyl hydrazone and antimycin A on ATP synthesis were examined in cells subjected to different starvation periods to reduce the endogenous ATP pool below the luciferase ATP saturation level (< or =0.2 mM). We conclude that the amount of endogenous ATP generated by light is maximal in the presence of oxygen, which is required to optimize the membrane redox poise.
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PMID:Assay of ATP in intact cells of the facultative phototroph Rhodobacter capsulatus expressing recombinant firefly luciferase. 1179 39

Biotrickling filters for air pollution control are expected to encounter fluctuating conditions or periods without pollutant supply. In the present study, we investigated the effect of pollutant starvation in bench-scale biotrickling filters treating toluene. The experimental protocol consisted of starving biotrickling filters under various conditions: with or without airflow, with or without liquid recycle, and with or without an alternate carbon source (glucose) supply. The duration of the period without toluene was varied from 2 to 9 days, during time which the biotrickling filters were monitored for biomass content, endogenous and toluene-induced oxygen uptake rates during starvation, and toluene overall elimination capacity after restart. During starvation, all reactors lost their ability to degrade toluene within 5 days, regardless of the mode of starvation. The biomass content significantly decreased during starvation, in particular in those reactors where the recycle liquid was maintained, but this decrease was not critical for future re-acclimation. Glucose addition to starved biotrickling filters had several detrimental effects. It resulted in a faster decrease of the biomass content and slowed the reacclimation phase. Overall, the results show that the reacclimation of toluene-degrading biotrickling filters after periods of nonuse is short (10-24 h to re-establish full performance), and they suggest that, in the case of toluene-degrading biotrickling filters, re-acclimation time is largely governed by the induction of key pollutant-degrading enzymes.
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PMID:Effect of starvation on the performance and re-acclimation of biotrickling filters for air pollution control. 1214 84

Transcription of the catabolic touABCDEF operon, encoding the toluene-o-xylene monooxygenase of Pseudomonas stutzeri OX1, is driven by the sigma(54)-dependent Ptou promoter, whose activity is controlled by the phenol-responsive NtrC-like activator TouR. In this paper we describe for the first time a peculiar characteristic of this system, namely, that Ptou transcription is activated in a growth phase-dependent manner in the absence of genuine effectors of the cognate TouR regulator. This phenomenon, which we named gratuitous activation, was observed in the native strain P. stutzeri OX1, as well as in a Pseudomonas putida PaW340 host harboring the reconstructed tou regulatory circuit. Regulator-promoter swapping experiments demonstrated that the presence of TouR is necessary and sufficient for imposing gratuitous activation on the Ptou promoter, as well as on other sigma(54)-dependent catabolic promoters, whereas the highly similar phenol-responsive activator DmpR is unable to activate the Ptou promoter in the absence of effectors. We show that this phenomenon is specifically triggered by carbon source exhaustion but not by nitrogen starvation. An updated model of the tou regulatory circuit is presented.
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PMID:TouR-mediated effector-independent growth phase-dependent activation of the sigma54 Ptou promoter of Pseudomonas stutzeri OX1. 1548 47

Continuous operation of a new bioreactor for air pollution control called the foamed emulsion bioreactor (FEBR) has been investigated. The effect of several liquid feeding strategies was explored. The FEBR exhibited high and steady toluene removal performance (removal efficiency of 89%-94%, elimination capacity of 214-226 g/m3h at toluene inlet concentration of 1 g/m3) for up to 360 h, when 20% of the culture was replaced every 24 h by a nutrient solution containing 4 g/L of potassium nitrate as a nitrogen source. This feeding mode supported a high cell activity measured as INT reduction potential and active cell growth without being subject to nitrogen limitation. In comparison, operating the FEBR with the liquid in a closed loop (i.e., batch) resulted in a significant decrease of both the removal efficiency of toluene and INT reduction activity. Operation with feeding active cells resulted in stable and effective treatment, but would require a significant effort for mass culture preparation. Therefore, the continuous process with periodically feeding nutrients was found to be the most practical and effective operating mode. It also allows for stable operation, as was shown during removal of low concentration of toluene or after pollutant starvation. Throughout the study, INT reduction measurements provided insight into the process. INT reduction activity data proved that under normal operating conditions, the FEBR performance was limited by both the kinetics and by mass transfer. Overall, the results illustrate that engineered gas-phase bioreactors can potentially be more effective than conventional biofilters and biotrickling filters for the treatment of air pollutants such as toluene.
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PMID:Continuous operation of foamed emulsion bioreactors treating toluene vapors. 1604 6

Subsurface bacteria commonly exist in a starvation state with only periodic exposure to utilizable sources of carbon and energy. In this study, the effect of carbon starvation on aerobic toluene degradation was quantitatively evaluated with a selection of bacteria representing all the known toluene oxygenase enzyme pathways. For all the investigated strains, the rate of toluene biodegradation decreased exponentially with starvation time. First-order deactivation rate constants for TMO-expressing bacteria were approximately an order of magnitude greater than those for other oxygenase-expressing bacteria. When growth conditions (the type of growth substrate and the type and concentration of toluene oxygenase inducer) were varied in the cultures prior to the deactivation experiments, the rate of deactivation was not significantly affected, suggesting that the rate of deactivation is independent of previous substrate/inducer conditions. Because TMO-expressing bacteria are known to efficiently detoxify TCE in subsurface environments, these findings have significant implications for in situ TCE bioremediation, specifically for environments experiencing variable growth-substrate exposure conditions.
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PMID:Effect of carbon starvation on toluene degradation activity by toluene monooxygenase-expressing bacteria. 1647 58

Pseudomonas putida mt-2(pWWO) exhibited a carbon starvation response in the presence of toluene, a utilizable carbon source. When growth-supporting (4-mg/liter), inhibitory (130-mg/liter), and lethal (267-mg/ liter) levels of toluene were provided as the sole carbon source, P. putida responded by rapidly inhibiting protein synthesis and by producing 26 new proteins, 22 of which overlapped with those induced by carbon starvation. P. putida produced the same proteins when cultures were starved by depleting their carbon source or were downshifted into a carbon-free medium. Carbon supplementation of toluene-exposed cells suppressed the production of the toluene-induced proteins. The level of toluene provided as the sole carbon source influenced the length of time that this response was observed. Following 1.5 to 3 h in a basal salts medium with 4 mg of toluene per liter, protein synthesis increased, the production of the majority of the toluene-induced proteins ceased, and the cells began to grow. In cells provided with 130 mg of toluene per liter, protein synthesis remained inhibited over a 6.5-h experimental period. At this concentration, the production of 15 toluene-induced proteins was prolonged, with nine still detectable in the profiles at 6.5 h. In cells provided with 267 mg of toluene per liter, there was a rapid loss of viability and the toluene-induced proteins were detected prior to death. In cells provided with 4 mg of toluene per liter, the carbon starvation response is transient and likely reflects a period of induction and/or adaptation prior to growth on toluene. At the toluene concentrations which inhibit growth, P. putida exhibits a prolonged starvation response despite the presence of an excess of a utilizable carbon source.
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PMID:Toluene Elicits a Carbon Starvation Response in Pseudomonas putida mt-2 Containing the TOL Plasmid pWW0. 1653 5

The effects of temporal and spatial changes in biological activity and biomass amount on biofilter performance were investigated in a lab-scale trickle-bed air biofilter at a toluene loading of 46.9gm(-3)h(-1) under two different experimental strategies, namely, periodic backwashing at a rate of 1h once a week and 2d starvation. Analysis of the overall reaction for toluene metabolism revealed that cell synthesis was relatively favored over toluene oxidation in the inlet section of the biofilter, but over time its oxidation became favored throughout the biofilter bed. Periodic in situ backwashing with media fluidization effectively made even spatial distribution of biomass along the bed media, by which consistent high removal performance in the biofilter has been attained. After 2d starvation, the ratio of the biofilm EPS to the total biomass increased along the media bed depth, while the total biomass in the media bed subsequently decreased. The presence of sufficient biomass and microbial activity favorably influenced biofilter reacclimation after restart-up following starvation.
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PMID:Role of biological activity and biomass distribution in air biofilter performance. 1689 Sep 77

Two independent parallel trickling bed air biofilters (TBABs) ("A" and "B") with two different typical VOC mixtures were investigated. Toluene, styrene, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK) were the target VOCs in the mixtures. Biofilter "A" was fed equal molar ratio of the VOCs and biofilter "B" was fed a mixture based on EPA 2003 emission report. Backwashing and substrate starvation operation were conducted as biomass control. Biofilter "A" and "B" maintained 99% overall removal efficiency for influent concentration up to 500 and 300 ppmv under backwashing operating condition, respectively. The starvation study indicated that it can be an effective biomass control for influent concentrations up to 250 ppmv for biofilter "A" and 300 ppmv for "B". Re-acclimation of biofilter performance was delayed with increase of influent concentration for both biofilters. Starvation operation helped the biofilter to recover at low concentrations and delayed re-acclimation at high concentrations. Furthermore, re-acclamation for biofilter "B" was delayed due to its high toluene content as compared to biofilter "A". The pseudo first-order removal rate constant decreased with increase of volumetric loading rate for both biofilters. MEK and MIBK were completely removed in the upper 3/8 media depth. While biofilter depth utilization for the removal of styrene and toluene increased with increase of influent concentrations for both biofilters. However, toluene removal utilized more biofilter depth for biofilter "B" as compared to biofilter "A".
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PMID:A comparative study in treating two VOC mixtures in trickle bed air biofilters. 1734 73

Biological waste gas treatment is an attractive method for controlling air emissions of volatile organic compounds (VOCs). Microorganisms degrade the VOCs to harmless products such as carbon dioxide (CO(2)), biomass and water. In spite of the advantages, significant unresolved challenges remain for biological waste gas treatment. Fluctuating loads in waste gas streams, especially of VOCs with low water solubility, can often not be satisfactorily removed. Concentration peaks leave the reactor virtually untreated, while periods without VOCs in the waste gas lead to starvation of the bacteria. Furthermore, bioreactors are often subject to clogging due to biomass accumulation. In the current work, a flat sheet membrane bioreactor was developed which was able to buffer fluctuating loads of toluene, our model compound, by absorption in silicone oil prior to degradation and which continuously removed and discharged excess biomass from the reactor. The absorption and the biodegradation were both membrane based. An inverse bacterial biofilm developed on the membrane, which separated the culture medium from the absorbent. The culture medium was constantly passed along the biofilm, introducing shear stresses on the surface and thereby removing excess, inactive biomass. The toluene surface elimination capacity was virtually independent of the gas flow rate for the tested steady-state conditions and reached a maximum of 0.6 g m(-2) h(-1). Experiments with fluctuating inlet mass flow rates of toluene confirmed the excellent buffering capability of the set-up. The reactor was successfully operated for 162 days without clogging.
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PMID:Novel membrane bioreactor: Able to cope with fluctuating loads, poorly water soluble VOCs, and biomass accumulation. 1757 Jul 7


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