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1.
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 Y ATP for glucose and xylose was 9.9 and 5.1 g of DCM/mol of ATP, respectively. Y ATP 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 Y a/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 (Y ATP=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, Y ATP=8.71 and m=2.05g of glu/(g of cell…h) whereas at D<0.1/h, Y ATP=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. 相似文献
2.
Lime (Ca[OH] 2) and oxygen (O 2) were used to enhance the enzymatic digestibility of two kinds of high-lignin biomass: poplar wood and newspaper. The recommended
pretreatment conditions for poplar wood are 150°C, 6 h, 0.1 g of Ca(OH) 2/g of dry biomass, 9 mL of water/g of dry biomass, 14.0 bar absolute oxygen, and a particle size of −10 mesh. Under these
conditions, the 3-d reducing sugar yield of poplar wood using a cellulase loading of 5 filter paper units (FPU)/g of raw dry
biomass increased from 62 to 565 mg of eq. glucose/g of raw dry biomass, and the 3-d total sugar (glucose + xylose) conversion
increased from 6 to 77% of raw total sugars. At high cellulase loadings (e.g., 75 FPU/g of raw dry biomass), the 3-d total
sugar conversion reached 97%. In a trial run with newspaper, using conditions of 140°C, 3 h, 0.3 g of Ca(OH) 2/g of dry biomass, 16 mL of water/g of dry biomass, and 7.1 bar absolute oxygen, the 3-d reducing sugar yield using a cellulase
loading of 5 FPU/g of raw dry biomass increased from 240 to 565 mg of eq. glucose/g of raw dry biomass. A material balance
study on poplar wood shows that oxidative lime pretreatment solubilized 38% of total biomass, including 78% of lignin and
49% of xylan; no glucan was removed. Ash increased because calcium was incorporated into biomass during the pretreatment.
After oxidative lime pretreatment, about 21% of added lime could be recovered by CO 2 carbonation. 相似文献
3.
Lime (calcium hydroxide) was used as a pretreatment agent to enhance the enzymatic digestibility of two common crop residues:
bagasse and wheat straw. A systematic study of pretreatment conditions suggested that for short pretreatment times (1–3 h),
high temperatures (85-135°C) were required to achieve high sugar yields, whereas for long pretreatment times (e.g., 24 h),
low temperatures (50–65°C) were effective. The recommended lime loading is 0.1 g Ca(OH) 2/g dry biomass. Water loading had little effect on the digestibility. Under the recommended conditions, the 3-d reducing sugar
yield of the pretreated bagasse increased from 153 to 659 mg Eq glucose/g dry biomass, and that of the pretreated wheat straw
increased from 65 to 650 mg Eq glucose/g dry biomass. A material balance study on bagasse showed that the biomass yield after
lime pretreatment is 93.6%. No glucan or xylan was removed from bagasse by the pretreatment, whereas 14% of lignin became
solubilized. A lime recovery study showed that 86% of added calcium was removed from the pretreated bagasse by ten washings
and could be recovered by carbonating the wash water with CO 2 at pH 9.5. 相似文献
4.
Azadirachtin, a well-known biopesticide is a secondary metabolite conventionally extracted from the seeds of Azadirachta indica. The present study involved in vitro azadirachtin production by developing hairy roots of A. indica via Agrobacterium rhizogenes-mediated transformation of A. indica explants. Liquid culture of hairy roots was established in shake flask to study the kinetics of growth and azadirachtin production.
A biomass production of 13.3 g/L dry weight (specific growth rate of 0.7 day −1) was obtained after 25 days of cultivation period with an azadirachtin yield of 3.3 mg/g root biomass. To overcome the mass
transfer limitation in conventionally used liquid-phase reactors, batch cultivation of hairy roots was carried out in gas-phase
reactors (nutrient spray and nutrient mist bioreactor) to investigate the possible scale-up of A. indica hairy root culture. The nano-size nutrient mist particles generated from the nozzle of the nutrient mist bioreactor could
penetrate till the inner core of the inoculated root matrix, facilitating uniform growth during high-density cultivation of
hairy roots. A biomass production of 9.8 g/L dry weight with azadirachtin accumulation of 2.8 mg/g biomass (27.4 mg/L) could
be achieved in 25 days of batch cultivation period, which was equivalent to a volumetric productivity of 1.09 mg/L per day
of azadirachtin. 相似文献
5.
We report the antibacterial efficacies of silver and/or silver chloride containing titania xerogels synthesized with modified
single step sol-gel methods against Escherichia coli bacteria. As the silver loading in TiO 2 increases, the amount of the xerogel required to inhibit the growth of the bacteria decreases and also we found that pure
TiO 2 was not bactericidal. Among modified single step sol-gel methods used in this study, the additional HCl treatment sol-gel
route III was very effective to obtain only AgCl crystallites in TiO 2. Based on viable cell count method, 0.125 g/L of 29%Ag/TiO 2 (made with HNO 3 sol-gel route I) was enough to inhibit the growth of E. coli whereas 0.6 g/L of 29%Ag/TiO 2 (made with the additional HCl treatment sol-gel route III) was required. However, antibacterial activity of 29%Ag/TiO 2 (made with HNO 3 sol-gel route I) after 6 usages was the same as 29%Ag/TiO 2 (made with the additional HCl treatment sol-gel route III). 相似文献
6.
Glucose/xylose mixtures (90 g/L total sugar) were evaluated for their effect on ethanol fermentation by a recombinant flocculent Saccharomyces cerevisiae, MA-R4. Glucose was utilized faster than xylose at any ratio of glucose/xylose, although MA-R4 can simultaneously co-ferment both sugars. A high percentage of glucose can increase cell biomass production and therefore increase the rate of glucose utilization (1.224 g glucose/g biomass/h maximum) and ethanol formation (0.493 g ethanol/g biomass/h maximum). However, the best ratio of glucose/xylose for the highest xylose consumption rate (0.209 g xylose/g biomass/h) was 2:3. Ethanol concentration and yield increased and by-product (xylitol, glycerol, and acetic acid) concentration decreased as the proportion of glucose increased. The maximum ethanol concentration was 41.6 and 21.9 g/L after 72 h of fermentation with 90 g/L glucose and 90 g/L xylose, respectively, while the ethanol yield was 0.454 and 0.335 g/g in 90 g/L glucose and 90 g/L xylose media, respectively. High ethanol yield when a high percentage of glucose is available is likely due to decreased production of by-products, such as glycerol and acetic acid. These results suggest that ethanol selectivity is increased when a higher proportion of glucose is available and reduced when a higher proportion of xylose is available. 相似文献
7.
The influences of urea, yeast extract, and nitrate as the nitrogen source on heterotrophic growth of four strains of Chlorella protothecoides were investigated in 9-day feed-batch cultures. Biomass dry weight concentration (DWC) and lipid yield (LY) of the four strains
in all media were compared. The highest LY in 9 days was 654 mg/L/day by UTEX 255 in 2.4 g/L KNO 3 medium with a biomass DWC of 11.7 g/L and lipid content of 50.5%. Using green autotrophic seeds instead of yellow heterotrophic
seeds improved the biomass DWC (13.1 vs. 11.7 g/L), LY (850 vs. 654 mg/L/day), and lipid to glucose consumption ratio (0.607
vs. 0.162). Moreover, 17.0 g/L DWC and 489 mg/L/day LY were obtained from the sequentially mixed-nitrogen medium, and the
lipid to glucose consumption ratio was improved to 0.197 from 0.162 in 2.4 g/L nitrate medium and from 0.108 in 4.2 g/L yeast
extract medium in the first batch. 相似文献
8.
Data on conversion of starch on biomass and ethanol by Schwanniomyces castellii in an aerobic-anaerobic solid state fermentation is reported. Schwanniomyces castellii grew exponentially in the aerobic phase (12 h) and simultaneously hydrolyzed nearly half (55%) of the starch initially present.
The accumulation of glucose increased up to 12 h, whereas maltose was nearly absent beyond 7 h. Shift of metabolism from oxidative
to fermentative pattern was observed about 10 h as a result of the build-up of CO 2 level and faster utilization of O 2. The ethanol production in the anaerobic phase reached the level of 89.3 mg ethanol/g initial dry matter by the end of 30
h. A total of 92.9% of the starch is utilized during the fermentation. The overall ethanol conversion yields are 57.8% of
the theoretical value, whereas in the anaerobic phase it was found to be 94.4%. The cell shape, its morphology, and the type
of attachment to the solid support were found to be similar in aerobic and anaerobic phases of fermentation. Data given in
this work indicate the feasibility of using one single fermenter for aerobic growth to generate inoculum as well as to simultaneously
hydrolyze the starch and subsequent anaerobic fermentation to produce ethanol. 相似文献
9.
Bacillus circulans D1 is a good producer of extracellular thermostable xylanase. Xylanase production in different carbon sources was evaluated
and the enzyme synthesis was induced by various carbon sources. It was found that d-maltose is the best inducer of the enzyme synthesis (7.05 U/mg dry biomass at 48 h), while d-glucose and d-arabinose lead to the production of basal levels of xylanase. The crude enzyme solution is free of cellulases, even when
the microorganism was cultivated in a medium with d-cellobiose. When oat spelt xylan was supplemented with d-glucose, the repressive effect of this sugar on xylanase production was observed at 24 h, only when used at 5.0 g/L, leading
to a reduction of 60% on the enzyme production. On the other hand, when the xylan medium was supplemented with d-xylose (3.0 or 5.0 g/L), this effect was more evident (80 and 90% of reduction on the enzyme production, respectively). Unlike
that observed in the xylan medium, glucose repressed xylanase production in the maltose medium, leading to a reduction of
55% on the enzyme production at 24 h of cultivation. Xylose, at 1.0 g/L, induced xylanase production on the maltose medium.
On this medium, the repressive effect of xylose, at 3.0 or 5.0 g/L, was less expressive when compared to its effect on the
xylan medium. 相似文献
10.
This study compared the anaerobic catabolism of glucose and xylose by a patented, recombinant ethanologenic Escherichia coli B 11303:pLOI297 in terms of overall yields of cell mass (growth), energy (ATP), and end product (ethanol). Batch cultivations
were conducted with pH-controlled stirred-tank bioreactors using both a nutritionally rich, complex medium (Luria broth) and
a defined salts minimal medium and growth-limiting concentrations of glucose or xylose. The value of Y ATP was determined to be 9.28 and 8.19 g dry wt cells/mol ATP in complex and minimal media, respectively. Assuming that the nongrowth-associated
energy demand is similar for glucose and xylose, the mass-based growth yield ( Y
x/s
, g dry wt cells/g sugar) should be proportional to the net energy yield from sugar metabolism. The value of Y
x/s
was reduced, on average, by about 50% (from 0.096 g/g glu to 0.051 g/g xyl) when xylose replaced glucose as the growth-limiting
carbon and energy source. It was concluded that this observation is consistent with the theoretical difference in net energy
(ATP) yield associated with anaerobic catabolism of glucose and xylose when differences in the mechanisms of energy-coupled
transport of each sugar are taken into account. In a defined salts medium, the net ATP yield was determined to be 2.0 and
0.92 for glucose and xylose, respectively. 相似文献
11.
Photosynthetic mitigation of CO2 through microalgae is gaining great importance due to its higher photosynthetic ability compared to plants, and the biomass can be commercially exploited for various applications. CO2 fixation capability of the newly isolated freshwater microalgae Scenedesmus bajacalifornicus BBKLP-07 was investigated using a 1-l photobioreactor. The cultivation was carried at varying concentration of CO2 ranging from 5 to 25%, and the temperature and light intensities were kept constant. A maximum CO2 fixation rate was observed at 15% CO2 concentration. Characteristic growth parameters such as biomass productivity, specific growth rate, and maximum biomass yield, and biochemical parameters such as carbohydrate, protein, lipid, chlorophyll, and carotenoid were determined and discussed. It was observed that the effect of CO2 concentration on growth and biochemical composition was quite significant. The maximum biomass productivity was 0.061 ± 0.0007 g/l/day, and the rate of CO2 fixation was 0.12 ± 0.002 g/l/day at 15% CO2 concentration. The carbohydrate and lipid content were maximum at 25% CO2 with 26.19 and 25.81% dry cell weight whereas protein, chlorophyll, and carotenoid contents were 32.89% dry cell weight, 25.07 μg/ml and 6.15 μg/ml respectively at 15% CO2 concentration. 相似文献
12.
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). 相似文献
13.
Native fungal biomass of fungi Absidia orchidis, Penicillium chrysogenum, Rhizopus arrhizus, Rhizopus nigricans, and modified spruce sawdust ( Picea engelmanii) sequestered metals in the following decreasing preference pb>Cd>Ni. The highest metal uptake was q max = 351 mg Pb/g A. orchidis biomass. P. chrysogenum biomass could accumulate cadmium best at 56 mg Cd/g. The sorption of nickel was the weakest always at < 5 mg Ni/g. The spruce
sawdust was modified by crosslinking, oxidation to acidic oxoforms, and by substitution. The highest metal uptake was observed
in phosphorylated sawdust reaching q max = 224 mg Pb/g, 56 mg Cd/g, and 26 mg Ni/g. The latter value is comparable to the value of nickel sorption by wet commercial
resin Duolite GT-73. Some improvement in metal uptake was also observed after reinforcement of fungal biomass. 相似文献
14.
The production of extracellular and mycelia-associated penicillin G acylase (maPGA) with Mucor griseocyanus H/55.1.1 by surface-adhesion fermentation using Opuntia imbricata, a cactus, as a natural immobilization support was studied. Enzyme activity to form 6-aminopencillanic acid (6-APA) from
penicillin G was assayed spectrophotometrically. The penicillin G hydrolysis to 6-APA was evaluated at six different times
using PGA samples recovered from the skim milk medium at five different incubation times. Additionally, the effect of varying
the penicillin G substrate concentration level on the PGA enzyme activity was also studied. The maximum reaction rate, V
max, and the Michaelis constant, K
M, were determined using the Michaelis–Menten model. The maximum levels for maPGA and extracellular activity were found to
be 2,126.50 international unit per liter (IU/l; equal to 997.83 IU/g of support) at 48 h and 755.33 IU/l at 60 h, respectively.
Kinetics of biomass production for total biomass showed a maximum growth at 60 h of 3.36 and 2.55 g/l (equal to 0.012 g of
biomass per gram of support) for the immobilized M. griseocyanus biomass. The maPGA was employed for the hydrolysis of penicillin G to obtain 6-APA in a batch reactor. The highest quantity
of 6-APA obtained was 226.16 mg/l after 40-min reaction. The effect of substrate concentration on maPGA activity was evaluated
at different concentrations of penicillin G (0–10 mM). K
M and V
max were determined to be 3.0 × 10 −3 M and 4.4 × 10 −3 mM/min, respectively. 相似文献
15.
A comparative study on Au/TiO 2catalysts prepared by impregnation with HAuCl 4of commercial TiO 2 or by impregnation of sol-gel derived TiO 2has been carried out during CO oxidation. Specific surface areas and mean Au particle of 49 and 74 m 2/g and 35 and 25 Å were obtained for impregnated commercial TiO 2 and sol-gel preparations, respectively. XRD patterns shown that in sol-gel derived TiO 2 only anatase phase was identified, while in commercial TiO 2 anatase and rutile phases co-exist. Titania support effect on Au activity for the oxidation of CO has been observed. The light-off during the reaction on Au/TiO 2initiates at 50°C, whereas for commercial impregnated TiO 2 catalyst the light-off initiates at 200°C. 相似文献
16.
Pyridylethylaminopropylpolysiloxane xerogel (PEAPPSX) was synthesized by sol-gel technology. The composition of the substance
was determined via elemental analysis and 1H NMR spectroscopy. The surface structural characteristics of the xerogel were
determined by electron microscopy and low-temperature nitrogen sorption; thermal analysis was also performed. It was established
that the content of functional groups in PEAPPSX was 2.43 mmol/g, and that xerogel is a mesoporous substance with a developed
surface (121.71 m 2/g). 相似文献
17.
The aim of this study was to monitor the biomass growth of Aspergillus niger in solid-state fermentation (SSF) for lipase production using digital image processing technique. The strain A. niger 11T53A14 was cultivated in SSF using wheat bran as support, which was enriched with 0.91% ( m/ v) of ammonium sulfate. The addition of several vegetable oils (castor, soybean, olive, corn, and palm oils) was investigated
to enhance lipase production. The maximum lipase activity was obtained using 2% ( m/ m) castor oil. In these conditions, the growth was evaluated each 24 h for 5 days by the glycosamine content analysis and digital
image processing. Lipase activity was also determined. The results indicated that the digital image process technique can
be used to monitor biomass growth in a SSF process and to correlate biomass growth and enzyme activity. In addition, the immobilized
esterification lipase activity was determined for the butyl oleate synthesis, with and without 50% v/ v hexane, resulting in 650 and 120 U/g, respectively. The enzyme was also used for transesterification of soybean oil and ethanol
with maximum yield of 2.4%, after 30 min of reaction. 相似文献
18.
Jerusalem artichoke is a low-requirement sugar crop containing cellulose and hemicellulose in the stalk and a high content of inulin in the tuber. However, the lignocellulosic component in Jerusalem artichoke stalk reduces the fermentability of the whole plant for efficient bioethanol production. In this study, Jerusalem artichoke stalk was pretreated sequentially with dilute acid and alkali, and then hydrolyzed enzymatically. During enzymatic hydrolysis, approximately 88 % of the glucan and xylan were converted to glucose and xylose, respectively. Batch and fed-batch simultaneous saccharification and fermentation of both pretreated stalk and tuber by Kluyveromyces marxianus CBS1555 were effectively performed, yielding 29.1 and 70.2 g/L ethanol, respectively. In fed-batch fermentation, ethanol productivity was 0.255 g ethanol per gram of dry Jerusalem artichoke biomass, or 0.361 g ethanol per gram of glucose, with a 0.924 g/L/h ethanol productivity. These results show that combining the tuber and the stalk hydrolysate is a useful strategy for whole biomass utilization in effective bioethanol fermentation from Jerusalem artichoke. 相似文献
19.
The production of lactic acid from glucose has been demonstrated using a CSTR (continuous stirred-tank reactor) with cell
recycle. Studies were conducted with Lactobacillus delbrueckii at a fermentation temperature of 42°C and a pH of 6.25. A cell density of 140 g dry weight/L and a volumetric productivity
of 150 g/L.h, with complete glucose consumption, were obtained. It was not possible to obtain a lactic acid concentration
above 60 g/L because of product inhibition. A cell purge was not necessary to maintain high viability bacteria culture or
to obtain a steady state. At steady state the net cell growth appeared to be negligible. The specific glucose consumption
for cell maintenance was 0.33 g glucose/g cells-h. 相似文献
20.
The structure and the biosorption properties of fungal biomass of Aspergillus niger originated from citric acid fermentation industry was investigated. This waste biomass, produced in high quantity in carefully
controlled industrial processes, has certain favourable characteristics that may be improved for its usefulness. In environmental
chemistry, it is known for the removal of heavy metals cations. In this work, different alkaline treatments (1M NaOH/20°C/24
h and 10M NaOH/107°C/6 h) were used to evaluate the dependence of sorption properties of biomass on the cell wall composition.
The biosorption was studied by the batch method, with the biomass concentration of 1 g/l, at pH 6. The adsorption of lead
was more effective than that of cadmium. The biosorption capacity was evaluated using the biosorption isotherm derived from
the equilibrium data. At pH 6, the maximmum lead biosorption capacity estimated with the Langmuir model was 93 mg/g dry biomass. 相似文献
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