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 18,428 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ability to produce cellulose and xylan degrading enzymes by different strains of Thecotheus pelletieri, in liquid synthetic media with cellulose and xylan as inducers, was compared. All the strains tested were able to grow and produce cellulases and xylanases, being the strain BAFC 2077 the best producer. Several cultural conditions were analysed in order to optimise enzyme production by strain 2077. Shaking cultures gave higher yields of cellulases and xylanases compared with stationary ones. Asparagine at 0.75 g N/L was the best nitrogen source in promoting enzyme production. The influence of different surfactants on enzyme production was studied. Tween 80 exhibited no effect on growth and enzyme production, whereas Tween 20 and Triton X-100 were inhibitory. By means of studies of variation of cellulose/xylan ratio in the culture medium we determined that cellulose and xylan induced cellulase and xylanase synthesis, being the specific substrates the most effective. The inducible behavior of cellulases and xylanases in T. pelletieri was determined by means of inhibition of protein synthesis by cycloheximide and ethidium bromide. Moreover, we found that glucose as well as xylose repressed cellulase and xylanase synthesis in T. pelletieri.
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PMID:Cellulose and xylan degrading enzymes in Thecotheus pelletieri. 1114 50

The yeast strain Candida guilliermondii 2581 was chosen for its ability to produce xylitol in media with high concentrations of xylose. The rate of xylitol production at a xylose concentration of 150 g/l is 1.25 g/l per h; the concentration of xylitol after three days of cultivation is 90 g/l; and the relative xylitol yield is 0.6 g per g substrate consumed. The growth conditions were found that resulted in the maximum relative xylitol yield with complete consumption of the sugar: xylose concentration, 150 g/l; pH 6.0; and shaking at 60 rpm. It was shown that the growth under conditions of limited aeration favors the reduction of xylose.
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PMID:[Formation of xylitol in Candida guilliermondii 2581 culture]. 1160 70

The global oxygen uptake rate (OUR) and specific oxygen uptake rates (SOUR) were determined for different values of the volumetric oxygen mass transfer coefficient (15, 43, and 108 h(-1)), and for varying initial xylose concentrations (50, 100, 150, and 200 g/L) in shaking flasks. The initial cell concentration was 4.0 g/L, and there was only significant growth in the fermentation with the highest oxygen availability. In this condition, OUR increased proportionally to cell growth, reaching maximum values from 2.1 to 2.5 g of O2/(L x h) in the stationary phase when the initial substrate concentration was raised from 50 to 200 g/L, respectively. SOUR showed different behavior, growing to a maximum value coinciding with the beginning of the exponential growth phase, after which point it decreased. The maximum SOUR values varied from 265 to 370 mg of O2/(g of cell x h), indicating the interdependence of this parameter and the substrate concentration. Although the volumetric productivity dropped slightly from 1.55 to 1.18 g of xylitol/(L x h), the strain producing capacity (Y(P/X)) rose from 9 to 20.6 g/g when the initial substrate concentration was increased from 50 to 200 g/L. As for the xylitol yield over xylose consumed (Y(P/S)), there was no significant variation, resulting in a mean value of 0.76 g/g. The results are of interest in establishing a strategy for controlling the dynamic oxygen supply to maximize volumetric productivity.
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PMID:Oxygen uptake rate in production of xylitol by Candida guilliermondii with different aeration rates and initial xylose concentrations. 1201 29

A xylanase producer WXULI-11 was isolated and identified as Pseudomonas sp. By combination treatment of WXULI-11 with UV and NTG, a mutant WLUN024 was obtained and its enzyme activity reached 354 IU/mL in 36 h by shaking flask. The mechanism of its xylanase production was primarily studied. The results showed that this enzyme was induced by xylan, xylose and some other xylosic material, while xylose had "two-way effect" on xylanase synthesis. Effects of nitrogen and other factors on enzyme production were also investigated.
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PMID:[Screening and fermentation conditions of a bacterial strain over-producing xylanase]. 1254 69

An Aspergillus giganteus strain was isolated as an excellent producer of xylanase associated with low levels of cellulase. Optimal xylanase production was obtained in liquid Vogel medium containing xylan as carbon source, pH 6.5 to 7.0, at 25 degrees C and under shaking at 120 rpm during 84 h. Among the several carbon sources tested, higher xylanase production was verified in xylan, xylose, sugar-cane bagasse, wheat bran and corn cob cultures, respectively. Optimal conditions for activity determination were 50 degrees C and pH 6.0. The xylanolytic complex of A. giganteus showed low thermal stability with T(50) of 2 h, 13 min and 1 min when it was incubated at 40, 50 and 60 degrees C, respectively, and high stability from pH 4.5 to 10.5, with the best interval between 7.0 to 7.5. This broad range of stability in alkali pH indicates a potential applicability in some industrial processes, which require such condition. Xylanolytic activity of A. giganteus was totally inhibited by Hg(+2), Cu(+2) and SDS at 10 mM. The analysis of the products from the oat spelts xylan hydrolysis through thin-layer chromatography indicated endoxylanase activity, lack of debranching enzymes and beta-xylosidase activity in assay conditions.
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PMID:Xylanolytic complex from Aspergillus giganteus: production and characterization. 1287 8

Green fluorescent protein (GFP) is a reporter that has had a significant impact due to its many advantages over other reporter genes: it is autofluorescent, it enables in situ detection, it is relatively small, and it is also nontoxic. By cloning a gene promoter upstream of the gfp gene and exposing the living cells transformed with the fusion to the specific inducer or repressor, gene expression can be real-time monitored by continuous quantitative measurement of the green fluorescence emitted by GFP. In this work, a promoter study using promoter-gfp fusions was conducted in 96-well plates. Because they were placed in an automated incubating and shaking microplate reader, the wells functioned as microscale bioreactors, allowing for parallel experiments and data analysis. In the study described here, an overexpression promoter (pBAD promoter) and two comparatively weak promoters (sodA and acnA in Escherichia coli SoxRS regulon) were studied in both endpoint and kinetics formats. Our results with the pBAD promoter revealed insight on its regulation, which is tightly controlled by levels of arabinose and glucose. Results on weak oxidative stress promoters (for sodA and acnA genes) were striking in that significant induction was observed when they were under a superoxide stress in plates. They both displayed dose-dependent induction to paraquat-generated superoxide anion, with sodA leading acnA in strength and time. These results, spanning highly inducible promoters for protein overexpression and weakly inducible promoters of metabolic interest, demonstrate that the approach is relatively easily executed and can be used for quantitative and temporal promoter studies in a high throughput format.
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PMID:A high-throughput approach to promoter study using green fluorescent protein. 1557 93

Inducible expression systems in which T7 RNA polymerase transcribes coding sequences cloned under control of a T7lac promoter efficiently produce a wide variety of proteins in Escherichia coli. Investigation of factors that affect stability, growth, and induction of T7 expression strains in shaking vessels led to the recognition that sporadic, unintended induction of expression in complex media, previously reported by others, is almost certainly caused by small amounts of lactose. Glucose prevents induction by lactose by well-studied mechanisms. Amino acids also inhibit induction by lactose during log-phase growth, and high rates of aeration inhibit induction at low lactose concentrations. These observations, and metabolic balancing of pH, allowed development of reliable non-inducing and auto-inducing media in which batch cultures grow to high densities. Expression strains grown to saturation in non-inducing media retain plasmid and remain fully viable for weeks in the refrigerator, making it easy to prepare many freezer stocks in parallel and use working stocks for an extended period. Auto-induction allows efficient screening of many clones in parallel for expression and solubility, as cultures have only to be inoculated and grown to saturation, and yields of target protein are typically several-fold higher than obtained by conventional IPTG induction. Auto-inducing media have been developed for labeling proteins with selenomethionine, 15N or 13C, and for production of target proteins by arabinose induction of T7 RNA polymerase from the pBAD promoter in BL21-AI. Selenomethionine labeling was equally efficient in the commonly used methionine auxotroph B834(DE3) (found to be metE) or the prototroph BL21(DE3).
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PMID:Protein production by auto-induction in high density shaking cultures. 1591 65

Xylitol, a five-carbon sugar alcohol, has many interesting applications in the food, pharmaceutical, and odontological industries, owing to its high sweetening power, its anticariogenic properties, and its insulin-independent metabolism. The bioconversion of detoxified hemicellulosic hydrolysate to xylitol by microorganisms could be a cheaper alternative to the current chemical process, since it is a simple process, with great specificity and low energy requirements. However, the success of fermentations for xylitol production depends on the productivity of the strain and its tolerance to different toxic or inhibitory compounds existing in the hydrolysates. In addition, a number of culture process parameters proved to have significant effects on xylitol production in hemicellulosic hydrolysate media. One of the most important control variables in this bioconversion is the aeration level, which affects the biochemical pathways in the xylose metabolism. The production of biomass is favored by aerobic conditions, while under anaerobic conditions xylose cannot be assimilated by yeast, whereas xylitol is formed in oxygen-limited incubation conditions. An adapted Candida sp. with enhanced resistance to the inhibitors in the hydrolysate can directly ferment the simply detoxified corn cob hemicellulosic hydrolysate to xylitol. In the present study, the combined effects of shaking speed, C/ N ratio, initial pH, and inoculum level on the fermentation of corn cob hemicellulosic hydrolysate to xylitol by an adapted Candida sp. were investigated using an orthogonal experimental design in flask. As a result, the optimum fermentation conditions were as follows: 180 r/min, a C/N ratio of 50, initial pH 5.5, and an inoculum level of 5% (volume ratio). Moreover, the optimum concentration factor of hydrolysate varied between 3.0 and 3.72 was obtained. Based on these results, in order to evaluate the effect of aeration rate on the fermentation of corn cob hemicellulosic hydrolysate to xylitol in fermentor, batch fermentations were carried out in a 3.7 L stirred fermentor using four different aeration strategies, including three kind of two-stage aeration strategies, which provided relatively high aeration rate in the early stage but reduced it in the later stage, and including a one-stage aeration strategy provided a constant aeration rate. With respect to xylitol yield, the results indicated that two-stage aeration strategy was significantly superior to one-stage aeration strategy. The highest xylitol yield (0.75 g/g) was obtained with oxygen supply strategy C (3.75 L/min for first 24 h, then lowered it to 1.25 L/min, 2.5 L fermentation medium was employed). In this process, without extensive detoxification of hydrolysate, an adapted Candida sp. can efficiently ferment the simply treated corn cob hemicellulosic hydrolysate to xylitol under the optimized fermentation conditions. This work should help the development of an efficient process for producing xylitol from corn cob hemicellulosic hydrolysate on a larger scale by bioconversion.
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PMID:[Xylitol production from corn cob hemicellulosic hydrolysate by Candida sp]. 1596 26

Clostridium thermocellum JW20 (ATCC 31549), which was isolated from a Louisiana cotton bale, grew on cellulose, cellobiose, and xylooligomers and, after adaptation, on glucose, fructose, and xylose in the pH range of 7.5 to 6.1 with T(opt) of 60 degrees C, T(max) of 69 degrees C, and T(min) of above 28 degrees C. Doubling times during growth on cellulose and cellobiose were 6.5 and 2.5 h, respectively. The G+C content of the DNA was 40 mol% (chemical analysis). Growth on cellulose as substrate was totally inhibited in the presence of more than 125 mM sodium sulfate, 300 mM sodium chloride, 250 mM potassium chloride, 200 mM calcium chloride, 125 mM magnesium chloride, 40 mM lactate, or 250 mM acetate. The ratio of the fermentation products ethanol to acetate plus H(2) decreased when the culture was agitated. Agitation otherwise increased the rate of cellulose degradation in a growing culture but not under nongrowth conditions or with cell-free culture supernatant containing the extracellular cellulase. Shaking lowered the concentration of H(2) in the culture broth and thus minimized inhibition by the H(2) formed. Externally added H(2) caused an increased formation of ethanol during growth on cellulose or cellobiose. However, at an atmospheric pressure as high as 355 kPa (50 lb/in), H(2) did not cause significant growth inhibition beyond an increasing lag phase (up to 24 h). Several criteria to specifically prove the purity of C. thermocellum cultures were suggested.
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PMID:Characterization of Clostridium thermocellum JW20. 1634 27

A cell-free, insoluble cell wall fraction is described which floats on the surface of suspension cultures of Glycine max L. Merrill var. Acme cells. Its accumulation is governed by both the shaking speed and the medium volume, a shaking speed of 110 to 120 revolutions per minute with a medium volume of about 100 to 120 milliliters in a 250-milliliter flask being optimal. Various factors which could control the accumulation of the complex were tested and are discussed, and scanning electron micrographs of the complex being released from the cell surface are presented.The composition of the complex by weight is 46% galacturonic acid, 36% protein, 11% lignin (apparent), 4.4% arabinose, 2% ash, and 0.5% methyl ester. Evidence for an intimate relationship between the uronic acid and protein fractions is presented. The protein contains hydroxyproline, and the bulk of it is tightly bound to the complex, although a portion can be removed with high salt treatments.
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PMID:An extracellular macromolecular complex from the surface of soybean suspension cultures. 1665 64


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