Biomedical subjects

G Lidén

Publications and source records attributed to G Lidén.

At least 19 recordsLinked to original sources

PubMed2001

Use of dynamic step response for control of fed-batch conversion of lignocellulosic hydrolyzates to ethanol.

Optimization of fed-batch conversion of lignocellulosic hydrolyzates by the yeast Saccharomyces cerevisiae was studied. The feed rate was controlled using a step response strategy, in which the carbon dioxide evolution rate was used as input variable. The performance of the control strategy was examined using both an untreated and a detoxified dilute acid hydrolyzate, and the performance was compared to that obtained with a synthetic medium. In batch cultivation of the untreated hydrolyzate, only 23% of the hexose sugars were assimilated. However, by using the feed-back controlled fed-batch technique, it was possible to obtain complete conversion of the hexose sugars. Furthermore, the maximal specific ethanol productivity (q(E,max)) increased more than 10-fold, from 0.06 to 0.70 g g(-1) h(-1). In addition, the viability of the yeast cells decreased by more than 99% in batch cultivation, whereas a viability of more than 40% could be maintained during fed-batch cultivation. In contrast to untreated hydrolyzate, it was possible to convert the sugars in the detoxified hydrolyzate also in batch cultivation. However, a 50% higher specific ethanol productivity was obtained using fed-batch cultivation. During batch cultivation of both untreated and detoxified hydrolyzate a gradual decrease in specific ethanol productivity was observed. This decrease could largely be avoided in fed-batch cultivations.

Cellulose↗

PubMed2001

[Functionality of inhalation aerosols is inadequate or lost at low temperature].

Correct and safe performance of metered-dose inhalers are necessary for efficient treatment of asthma under all climatic conditions. The spray mechanism malfunctioned when canister temperature was below -15 degrees C. The range and propagation of the spray plume at canister temperatures below 10 degrees C deviated clearly from those at 20 degrees C. Also the composition and particle concentration of the spray plume at low temperatures differed from those at more normal temperatures. Information must be provided to the effect that a canister must not be cold when used.

Administration, Inhalation↗

PubMed2001

Weighing imprecision and handleability of the sampling cassettes of the IOM sampler for inhalable dust.

The weight stability of the sampling cassette of the IOM sampler for inhalable dust was tested in several weighing experiments. The results show that the reliability of repeated weighings was good, but the absorption of water vapour was slow and varied considerably among cassette specimen. The exponential time constant for water absorption was approximately 4 days, and 15-20 days were needed to obtain weight stability. With the help of cassette blanks the imprecision in dust weight could be held below 0.05 mg, if the cassettes were allowed one week's storage in the weighing room before weighing, both before and after sampling. The IOM sampling cassettes seem to consist of a few subsets, each with identical relative weight increase in a weighing room. To keep the variability low it is important that both the blanks and the cassettes used for sampling come from the same subset. Experiments indicate that the conducting plastic of the IOM sampling cassette may be replaced with another kind of plastic with similar electrical conductivity, but whose humidity absorption is 30 times lower. A lid, which is weighed with the cassette, was designed so that the potential dust loss from the cassette proper to the commercial transport clip was eliminated. A flow adapter, which simplifies the measurement of the air flow during personal sampling, was designed.

Air Pollutants, Occupational↗

PubMed2000

On-line control of fed-batch fermentation of dilute-acid hydrolyzates.

Dilute-acid hydrolyzates from lignocellulose are, to a varying degree, inhibitory to yeast. In the present work, dilute-acid hydrolyzates from spruce, birch, and forest residue, as well as synthetic model media, were fermented by Saccharomyces cerevisiae in fed-batch cultures. A control strategy based on on-line measurement of carbon dioxide evolution (CER) was used to control the substrate feed rate in a lab scale bioreactor. The control strategy was based solely on the ratio between the relative increase in CER and the relative increase in feed rate. Severely inhibiting hydrolyzates could be fermented without detoxification and the time required for fermentation of moderately inhibiting hydrolyzates was also reduced. The feed rate approached a limiting value for inhibiting media, with a corresponding pseudo steady-state value for CER. However, a slow decrease of CER with time was found for media containing high amounts of 5-hydroxymethyl furfural (HMF). The success of the control strategy is explained by the conversion of furfural and HMF by the yeast during fed-batch operation. The hydrolyzates contained between 1.4 and 5 g/l of furfural and between 2.4 and 6.5 g/l of HMF. A high conversion of furfural was obtained (between 65-95%) at the end of the feeding phase, but the conversion of HMF was considerably lower (between 12-40%).

Biomass↗

PubMed2000

Physiological effects of 5-hydroxymethylfurfural on Saccharomyces cerevisiae.

The physiological effects of 5-hydroxymethylfurfural (HMF) on Saccharomyces cerevisiae CBS 8066 in the presence and absence of furfural were studied. Experiments were carried out by pulse addition of HMF (2-4 g/l) as well as HMF (2 g/l) together with furfural (2 g/l) to batch cultivations of S. cerevisiae. Synthetic medium with glucose (50 g/l) as carbon and energy source was used. Addition of 4 g/l of HMF caused a decrease (approx. 32%) in the carbon dioxide evolution rate. Furthermore, the HMF was found to be taken up and converted by the yeast with a specific uptake rate of 0.14 (+/-0.03) g/g x h during both aerobic and anaerobic conditions, and the main conversion product was found to be 5-hydroxymethylfurfuryl alcohol. A previously unreported compound was found and characterized by mass spectrometry. It is suggested that the compound is formed from pyruvate and HMF in a reaction possibly catalysed by pyruvate decarboxylase. When HMF was added together with furfural, very little conversion of HMF took place until all of the furfural had been converted. Furthermore, the conversion rates of both furfural and HMF were lower than when added separately and growth was completely inhibited as long as both furfural and HMF were present in the medium.

Anaerobiosis↗

PubMed2000

Personal sampling in parallel with open-face filter cassettes and IOM samplers for inhalable dust--implications for occupational exposure limits.

Parallel personal sampling was carried out with the open-face filter cassette and the IOM sampler for inhalable dust for nine types of organic dust. Parallel samples numbering 749 were obtained from 152 plants. Extremely large values and outliers were disregarded, and the remaining data for each type of dust were divided into subsets according to type of product or work task, and analyzed with the aid of linear regression. The coefficient of regression for each subset ranged between 0.2 and 0.7. Hypothetical occupational exposure limits (OELs) for inhalable dust were calculated based on the linear relation obtained between the dust concentrations measured with the open-face filter cassette and the IOM sampler. The fraction of person days with time-weighted average (TWA) concentrations exceeding the calculated hypothetical OELs for inhalable dust was obtained from the distribution of measured TWA inhalable dust concentrations. Based on the results of this study and the difference in sampling efficiency for large particles between the two samplers, it was concluded that the numerical value of the OEL for inhalable dust may be set at approximately twice the numerical value of the corresponding limit value for "total dust." Additional consideration of recently discovered health effects, and technical and economical factors may result in other numerical values of future OELs for inhalable dust.

Air Pollutants, Occupational↗

PubMed1998

A new whole-body exposure chamber for human skin and lung challenge experiments--the generation of wheat flour aerosols.

A new whole-body exposure chamber for human skin and lung challenge offers possibilities for experimental exposure challenges carried out in clinical practice, for exposure of patients, in research and for investigations of the effects of exposure on the skin and in the respiratory tract. The chamber system can be used for both aerosols and gases. Dynamically controlled, the chamber is relatively easy to operate and to clean. Air exchange rates can be varied between 6-12/h. Initial studies with wheat flour have been carried out. The homogeneity and stability of the wheat flour aerosol concentration (the spatial and the temporal variation) inside the chamber can be kept at acceptable levels.

Administration, Cutaneous↗

PubMed1997

A collaborative European study of personal inhalable aerosol sampler performance.

Following the adoption of new international sampling conventions for inhalable, thoracic and respirable aerosol fractions, a working group of Comité Européen de Normalisation (CEN) drafted a standard for the performance of workplace aerosol sampling instruments. The present study was set up to verify the experimental, statistical and mathematical procedures recommended in the draft performance standard and to check that they could be applied to inhalable aerosol samplers. This was achieved by applying the tests to eight types of personal inhalable aerosol sampler commonly used for workplace monitoring throughout Europe. The study led to recommendations for revising the CEN draft standard, in order to simplify the tests and reduce their cost. However, some further work will be needed to develop simpler test facilities and methods. Several of the samplers tested were found to perform adequately with respect to the inhalable sampling convention, at least over a limited range of typical workplace conditions. In general the samplers were found to perform best in low external wind speeds, which are the test conditions thought to be closest to those normally found in indoor workplaces. The practical implementation of the CEN aerosol sampling conventions requires decisions on which sampling instruments to use, estimation of the likely impact that changing sampling methods could have on apparent exposures, and adjustment where necessary of exposure limit values. The sampler performance data obtained in this project were affected by large experimental errors, but are nevertheless a useful input to decisions on how to incorporate the CEN inhalable sampling convention into regulation, guidance and occupational hygiene practice.

Europe↗

PubMed1997

Physiological response to anaerobicity of glycerol-3-phosphate dehydrogenase mutants of Saccharomyces cerevisiae.

Mutants of Saccharomyces cerevisiae, in which one or both of the genes encoding the two isoforms of NAD-dependent glycerol-3-phosphate dehydrogenase had been deleted, were studied in aerobic batch cultures and in aerobic-anaerobic step change experiments. The respirofermentative growth rates under aerobic conditions with semisynthetic medium (20 g of glucose per liter) of two single mutants, gpd1 delta and gpd2 delta, and the parental strain (mu = 0.5 h-1) were almost identical, whereas the growth rate of a double mutant, gpd1 delta gpd2 delta, was approximately half that of the parental strain. Upon a step change from aerobic to anaerobic conditions in the exponential growth phase, the specific carbon dioxide evolution rates (CER) of the wild-type strain and the gpd1 delta strain were almost unchanged. The gpd2 delta mutant showed an immediate, large (> 50%) decrease in CER upon a change to anaerobic conditions. However, after about 45 min the CER increased again, although not to the same level as under aerobic conditions. The gpd1 delta gpd2 delta mutant showed a drastic fermentation rate decrease upon a transition to anaerobic conditions. However, the CER values increased to and even exceeded the aerobic levels after the addition of acetoin. High-pressure liquid chromatographic analyses demonstrated that the added acetoin served as an acceptor of reducing equivalents by being reduced to butanediol. The results clearly show the necessity of glycerol formation as a redox sink for S. cerevisiae under anaerobic conditions.

Acetoin↗

PubMed1996

Dynamics of ammonia uptake in nitrogen limited anaerobic cultures of Saccharomyces cerevisiae.

Dynamics of the ammonia uptake by Saccharomyces cerevisiae under anaerobic conditions was studied in ammonia limited continuous cultures. A large number of pulse additions of ammonia (25-100 mg 1(-1)) were made at different dilution rates (0.05-0.20 h-1). The response was followed by on-line monitoring of the carbon dioxide evolution rate (CER), optical density, and by frequent analysis of extra- and intracellular metabolites. The uptake of a pulse of ammonia proceeded in a qualitatively highly reproducible pattern. Initially, a rapid and growth rate dependent uptake of ammonia was observed (lasting for about 10-15 min). Next followed a phase with little uptake (approx. 5 min). Finally, the rest of the ammonia pulse was taken up at a somewhat smaller rate which also depended on the growth rate. The first phase coincided with an increase in CER caused by mobilization of the intracellular carbohydrate trehalose and subsequently of glycogen. Regardless of dilution rate and the amount of ammonia added, the initial high uptake rate of ammonia was maintained until approximately the same amount of ammonia had been taken up. Transition from the first to the second uptake phase was associated with an increased glycerol production, indicating an elevated anabolic activity.

Ammonia↗

PubMed1996

The effects of pantothenate deficiency and acetate addition on anaerobic batch fermentation of glucose by Saccharomyces cerevisiae.

Physiological effects of deficiency of pantothenate, a necessary precursor in the synthesis of coenzyme A, were studied using the yeast strain Saccharomyces cerevisiae CBS 8066. Cells were grown on defined media in anaerobic batch cultures with glucose (50 g/l) as the carbon and energy source. Batch cultures containing more than 60 micrograms/l pantothenate showed no significant differences with respect to growth rates and product yields. However, with an initial pantothenate concentration at 30 micrograms/l, the average glucose consumption rate was 50% lower than in rich medium and, at even lower concentration of pantothenate, the culture did not consume all the glucose in the medium. Furthermore, pantothenate deficiency caused the acetate and pyruvate yields to increase and the biomass yield to decrease, compared to the yields in pantothenate-rich medium. The increased acetate formation could be counteracted by initial addition of acetate to the medium, and thereby the glycerol yield could be decreased. An initial addition of acetate of 1.6 g/l to pantothenate-deficient medium (30 micrograms/l) caused a 35% decrease in glycerol yield and a 6% increase in ethanol yield. Furthermore, the time required for complete conversion of the glucose decreased by 40%. Acetate addition affected the acetate and glycerol yields in a similar way in pantothenate-rich medium (1000 micrograms/l) also.

Acetates↗

PubMed1996

Physiological effects of nitrogen starvation in an anaerobic batch culture of Saccharomyces cerevisiae.

The effects of nitrogen starvation on the anaerobic physiology of Saccharomyces cerevisiae were studied in cells cultivated in a bioreactor. The composition of the mineral medium was designed such that the nitrogen source became depleted while there was still ample glucose left in the medium. The culture was characterized by acoustic gas analysis, flow injection analysis and HPLC analysis of extracellular substrates and metabolites. During the cultivation, the macromolecular composition of the cells was analysed with respect to the cellular content of RNA, protein, trehalose and glycogen. During exponential growth under anaerobic conditions, the maximum specific growth rate conditions. Depletion of ammonium in the medium led to an abrupt decrease (mumax) of S. cerevisiae CBS 8066 (0.46 h-1) was identical to the mumax determined under aerobic in the flux through glycolysis. Subsequently, a continuous decrease in the carbon dioxide evolution rate, caused by catabolite inactivation of the hexose-transport system, was observed. The apparent half-life of the transport system under nitrogen starvation was 13 h. During the exponential growth phase, the cellular content of RNA and protein was 15% (w/w) and 60% (w/w), respectively. At the end of the cultivation where the cells had been starved of nitrogen for 18 h, the cellular content of RNA and protein had decreased to 4% (w/w) and 22% (w/w), respectively. The intracellular carbohydrate content increased dramatically as trehalose and glycogen accumulated to final concentrations of 7% (w/w) and 25% (w/w), respectively. Glycerol formation during nitrogen starvation was higher than that accounted for by the formation of organic acids, suggesting a protein turnover of approximately 6% h-1. The growth energetics of S. cerevisiae CBS 8066 also changed as a result of nitrogen starvation, and YxATP was observed to increase from 80 mmol g-1 during the exponential growth phase to more than 130 mmol g-1 towards the end of the cultivation. The presented results illustrate the effect of nitrogen starvation on glycerol formation, protein turnover, catabolite inactivation of the sugar-transport system, the cellular composition, the cell cycle and growth energetics.

Ammonia↗

PubMed1996

A glycerol-3-phosphate dehydrogenase-deficient mutant of Saccharomyces cerevisiae expressing the heterologous XYL1 gene.

The gene XYL1, encoding a xylose reductase, from Pichia stipitis was transformed into a mutant of Saccharomyces cerevisiae incapable of glycerol production because of deletion of the genes GPD1 and GPD2. The transformed strain was capable of anaerobic glucose conversion in the presence of added xylose, indicating that the xylose reductase reaction can fulfill the role of the glycerol-3-phosphate dehydrogenase reaction as a redox sink. The specific xylitol production rate obtained was 0.38 g g-1 h-1.

Aldehyde Reductase↗

PubMed1996

Influence of the nitrogen source on Saccharomyces cerevisiae anaerobic growth and product formation.

To prevent the loss of raw material in ethanol production by anaerobic yeast cultures, glycerol formation has to be reduced. In theory, this may be done by providing the yeast with amino acids, since the de novo cell synthesis of amino acids from glucose and ammonia gives rise to a surplus of NADH, which has to be reoxidized by the formation of glycerol. An industrial strain of Saccharomyces cerevisiae was cultivated in batch cultures with different nitrogen sources, i.e., ammonium salt, glutamic acid, and a mixture of amino acids, with 20 g of glucose per liter as the carbon and energy source. The effects of the nitrogen source on metabolite formation, growth, and cell composition were measured. The glycerol yields obtained with glutamic acid (0.17 mol/mol of glucose) or with the mixture of amino acids (0.10 mol/mol) as a nitrogen source were clearly lower than those for ammonium-grown cultures (0.21 mol/mol). In addition, the ethanol yield increased for growth on both glutamic acid (by 9%) and the mixture of amino acids (by 14%). Glutamic acid has a large influence on the formation of products; the production of, for example, alpha-ketoglutaric acid, succinic acid, and acetic acid, increased compared with their production with the other nitrogen sources. Cultures grown on amino acids have a higher specific growth rate (0.52 h-1) than cultures of both ammonium-grown (0.45 h-1) and glutamic acid-grown (0.33 h-1) cells. Although the product yields differed, similar compositions of the cells were attained. The NADH produced in the amino acid, RNA, and extracellular metabolite syntheses was calculated together with the corresponding glycerol formation. The lower-range values of the theoretically calculated yields of glycerol were in good agreement with the experimental yields, which may indicate that the regulation of metabolism succeeds in the most efficient balancing of the redox potential.

Amino Acids↗

PubMed1995

Energetics and product formation by Saccharomyces cerevisiae grown in anaerobic chemostats under nitrogen limitation.

Anaerobic fermentation of glucose (20 g/l) by Saccharomyces cerevisiae CBS 8066 was studied in a chemostat (dilution rate = 0.05-0.25 h-1) at different concentrations of the nitrogen source (5.00 g/l or 0.36 g/l ammonium sulphate). The ethanol yield (g ethanol produced/g glucose consumed) was found to be higher and the glycerol yield (g glycerol formed/g glucose consumed) lower during nitrogen limitation than under carbon limitation. The biomass yield on ATP (g dry weight biomass produced/mol ATP consumed), was consequently found to be lower during nitrogen-limited conditions.

Adenosine Triphosphate↗

PubMed1994

The bone-anchored hearing aid: principal design and audiometric results.

The principle of the bone-anchored hearing aid (BAHA) is simple: sound vibrations are directly transmitted to the skull bone via a skin-penetrating titanium implant, and then are further transmitted to the cochlea, bypassing the middle ear. The present paper summarized the audiometric results from 122 patients with an average follow-up time of 5.6 years. When herein-suggested indications for treatment with the bone-anchored sound processor HC 300 are followed, the success rate is very high. The improved quality of life reported by the patients is a combination of improved quality of sound (warble tone threshold, speech reception threshold, and discrimination in noise), improved comfort, and relief from middle ear and ear canal disease occasioned by conventional hearing aids.

Audiometry↗

PubMed1991

Comparison of measured respirable dust sampler penetration curves with sampling conventions.

Measured sampler penetration curves are presented for British personal cyclone samplers and the MRE 113A static horizontal elutriator in calm air. These curves are compared with previous results for these instruments, and with theoretical models of sampler behaviour. The sampling efficiency of the elutriator when facing a moderate wind is discussed. The penetration curves are assessed by comparison with standard sampling conventions for respirable dust.

Air Pollutants, Occupational↗

PubMed1990

Ten years of experience with the Swedish bone-anchored hearing system.

In 1977, a new phase began in hearing rehabilitation of patients with chronic middle and external diseases and atresias. Thus far, these patients have had to rely on conventional bone conduction and air conduction devices that for various reasons give poor rehabilitation. The principle of the new treatment, made possible by the Swedish bone-anchored hearing system, is simple: sound vibrations are directly transmitted to the skull bone via a skin-penetrating titanium implant and then are further transmitted to the cochlea, bypassing the middle ear. The present paper summarizes our results in 147 patients over 10 years, including a total of 6,334 follow-up months. No significant rate of skin infections was observed. In over 93% of the observations, no sign of adverse skin reaction was seen. When herein-suggested indications for treatment with the bone-anchored sound processor HC-200 are followed, the success rate is over 90%. The improved quality of life reported by the patients is a combination of improved quality of sound, improved comfort, and relief from middle ear and ear canal disease occasioned by conventional hearing aids.

Adolescent↗