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1.
A novel enzymatic route for the synthesis of 2-amino-2,3-dimethylbutyramide (ADBA), important intermediate of highly potent
and broad-spectrum imidazolinone herbicides, from 2-amino-2,3-dimethylbutyronitrile (ADBN) was developed. Strain Rhodococcus boritolerans CCTCC M 208108 harboring nitrile hydratase (NHase) towards ADBN was screened through a sophisticated colorimetric screening
method and was found to be resistant to cyanide (5 mM). Resting cells of R. boritolerans CCTCC M 208108 also proved to be tolerant against high product concentration (40 g l −1) and alkaline pH (pH 9.3). A preparative scale process for continuous production of ADBA in both aqueous and biphasic systems
was developed and some key parameters of the biocatalytic process were optimized. Inhibition of NHase by cyanide dissociated
from ADBN was successfully overcome by temperature control (at 10°C). The product concentration, yield and catalyst productivity
were further improved to 50 g l −1, 91% and 6.3 g product/g catalyst using a 30/70 (v/v) n-hexane/water biphasic system. Furthermore, cells of R. boritolerans CCTCC M 208108 could be reused for at lease twice by stopping the continuous reaction before cyanide concentration rose to
2 mM, with the catalyst productivity increasing to 12.3 g product/g catalyst. These results demonstrated that enzymatic synthesis
of ADBA using whole cells of R. boritolerans CCTCC M 208108 showed potential for industrial application. 相似文献
2.
Sugar maple hemicellulosic hydrolysate containing 71.9 g/l of xylose was used as an inexpensive feedstock to produce polyhydroxyalkanoates
(PHAs) by Burkholderia cepacia ATCC 17759. Several inhibitory compounds present in wood hydrolysate were analyzed for effects on cell growth and PHA production
with strong inhibition observed at concentrations of 1 g/l furfural, 2 g/l vanillin, 7 g/l levulinic acid, and 1 M acetic
acid. Gradual catabolism of lower concentrations of these inhibitors was observed in this study. To increase the fermentability
of wood hydrolysate, several detoxification methods were tested. Overliming combined with low-temperature sterilization resulted
in the highest removal of total inhibitory phenolics (65%). A fed-batch fermentation exhibited maximum PHA production after
96 h (8.72 g PHA/L broth and 51.4% of dry cell weight). Compositional analysis by NMR and physical–chemical characterization
showed that PHA produced from wood hydrolysate was composed of polyhydroxybutyrate (PHB) with a molecular mass ( M
N) of 450.8 kDa, a melting temperature ( T
m) of 174.4°C, a glass transition temperature ( T
g) of 7.31°C, and a decomposition temperature ( T
decomp) of 268.6°C. 相似文献
3.
A recombinant d-lyxose isomerase from Providencia stuartii was immobilized on Duolite A568 beads which gave the highest conversion of d-fructose to d-mannose among the various immobilization beads evaluated. Maximum activities of both the free and immobilized enzymes for
fructose isomerization were at pH 7.5 and 45°C in the presence of 1 mM Mn 2+. Enzyme half-lives were 14 and 30 h at 35°C and 3.4 and 5.1 h at 45°C, respectively. The immobilized enzyme in 300 g fructose/l
(replaced hourly), produced 75 g mannose/l at 35°C = 25% (w/w) yield with a productivity of 75 g mannose l −1 h −1 after 23 cycles. 相似文献
4.
A strain of Bacillus coagulans that converted mixed sugars of glucose, xylose, and arabinose to l-lactic acid with 85% yield at 50°C was isolated from composted dairy manure. The strain was tolerant to aldehyde growth inhibitors
at 2.5 g furfural/l, 2.5 g 5-hydroxymethylfurfural/l, 2.5 g vanillin/l, and 1.2 g p-hydroxybenzaldehyde/l. In a simultaneous saccharification and fermentation process, the strain converted a dilute-acid hydrolysate
of 100 g corn fiber/l to 39 g lactic acid/l in 72 h at 50°C. Because of its inhibitor tolerance and ability to fully utilize
pentose sugars, this strain has potential to be developed as a biocatalyst for the conversion of agricultural residues into
valuable chemicals. 相似文献
5.
2,3-Butanediol (2,3-BDO) is of considerable importance in the chemical, plastic, pharmaceutical, cosmetic, and food industries. The main bacterial species producing this compound are considered pathogenic, hindering large-scale productivity. The species Paenibacillus brasilensis is generally recognized as safe (GRAS) and is phylogenetically similar to P. polymyxa, a species widely used for 2,3-BDO production. Here, we demonstrate, for the first time, that P. brasilensis strains produce 2,3-BDO. Total 2,3-BDO concentrations for 15 P. brasilensis strains varied from 5.5 to 7.6 g/l after 8 h incubation at 32 °C in modified YEPD medium containing 20 g/l glucose. Strain PB24 produced 8.2 g/l of 2,3-BDO within a 12-h growth period, representing a yield of 0.43 g/g and a productivity of 0.68 g/l/h. An increase in 2,3-BDO production by strain PB24 was observed using higher concentrations of glucose, reaching 27 g/l of total 2,3-BDO in YEPD containing about 80 g/l glucose within a 72-h growth period. We sequenced the genome of P. brasilensis PB24 and uncovered at least six genes related to the 2,3-BDO pathway at four distinct loci. We also compared gene sequences related to the 2,3-BDO pathway in P. brasilensis PB24 with those of other spore-forming bacteria, and found strong similarity to P. polymyxa, P. terrae, and P. peoriae 2,3-BDO-related genes. Regulatory regions upstream of these genes indicated that they are probably co-regulated. Finally, we propose a production pathway from glucose to 2,3-BDO in P. brasilensis PB24. Although the gene encoding S-2,3-butanediol dehydrogenase (butA) was found in the genome of P. brasilensis PB24, only R,R-2,3- and meso-2,3-butanediol were detected by gas chromatography under the growth conditions tested here. Our findings can serve as a basis for further improvements to the metabolic capabilities of this little-studied Paenibacillus species in relation to production of the high-value chemical 2,3-butanediol. 相似文献
6.
A 2,3-dihydroxybiphenyl (2,3-DHBP) dioxygenase gene from a Rhodococcus sp. strain, named RrbphCI and involved in the degradation of polychlorinated biphenyls (PCBs), was synthesized. RrbphCI was expressed in Escherichia coli and its encoded enzyme was purified. SDS–PAGE analysis indicated that the size of the protein encoded by RrbphCI was about 32 kDa. The activity of the 2,3-DHBP dioxygenase was 82.8 U/mg when the substrate was 2,3-DHBP, with optimum pH
8.0 at 30°C, and optimum temperature was 40°C at pH 8.0. The RrbphCI gene was transformed into Pseudomonas
putida strain EG11, to determine the ability of the enzyme to degrade 2,3-DHBP. The wild type EG11 degraded 61.86% of supplied 2,3-DHBP
and the transformed EG11 (hosting the RrbphCI gene) utilized 52.68% after 2 min of treatment at 30°C. The overexpressed and purified enzyme was able to degrade 2,3-DHBP.
The 2,3-DHBP dioxygenase is a key enzyme in the PCB degradation pathway. RrbphCI and its encoded 2,3-DHBP dioxygenase may have transgenic applications in bioremediation of PCBs. 相似文献
7.
In the present study, the production of exopolysaccharides (EPS) by 13 strains of Lactobacillus and 6 strains of Bifidobacterium in a chemical defined medium (CDM) supplemented with 30 g lactose/l was first compared. The highest EPS production of the
Lactobacillus strains was found in L. salivarius BCRC 14759 while among the Bifidobacterium strains examined, B. bifidum BCRC 14615 showed the highest EPS production. Analyzes of the effect of lactose concentration and cultivation temperature
on EPS production revealed that L. salivarius produced the highest amount of EPS (45.3 mg/l) in CDM supplemented with 5 g lactose/l at 40°C while B. bifidum produced the highest EPS (17.0 mg/l) in CDM supplemented with 40 g lactose/l at 35°C. α-Phosphoglucomutase, UDP-glucose pyrophosphorylase
and UDP-galactose-4-epimerase exhibited a markedly notable activity compared with other enzymes examined in the cell extract
of both test organisms. This indicates their possible involvement in the biosynthesis of EPS. 相似文献
8.
Ethanol production by K. marxianus in whey from organic cheese production was examined in batch and continuous mode. The results showed that no pasteurization
or freezing of the whey was necessary and that K. marxianus was able to compete with the lactic acid bacteria added during cheese production. The results also showed that, even though
some lactic acid fermentation had taken place prior to ethanol fermentation, K. marxianus was able to take over and produce ethanol from the remaining lactose, since a significant amount of lactic acid was not produced
(1–2 g/l). Batch fermentations showed high ethanol yield (~0.50 g ethanol/g lactose) at both 30°C and 40°C using low pH (4.5)
or no pH control. Continuous fermentation of nonsterilized whey was performed using Ca-alginate-immobilized K. marxianus. High ethanol productivity (2.5–4.5 g/l/h) was achieved at dilution rate of 0.2/h, and it was concluded that K. marxianus is very suitable for industrial ethanol production from whey. 相似文献
9.
Ethanol production by recombinant Escherichia coli strain FBR5 from dilute acid pretreated wheat straw (WS) by separate hydrolysis and fermentation (SHF) and simultaneous saccharification
and fermentation (SSF) was studied. The yield of total sugars from dilute acid (0.5% H 2SO 4) pretreated (160 °C, 10 min) and enzymatically saccharified (pH 5.0, 45 °C, 72 h) WS (86 g/l) was 50.0 ± 1.4 g/l. The hydrolyzate
contained 1,184 ± 19 mg furfural and 161 ± 1 mg hydroxymethyl furfural per liter. The recombinant E. coli FBR5 could not grow at all at pH controlled at 4.5 to 6.5 in the non-abated wheat straw hydrolyzate (WSH) at 35 °C. However,
it produced 21.9 ± 0.3 g ethanol from non-abated WSH (total sugars, 44.1 ± 0.4 g/l) in 90 h including the lag time of 24 h
at controlled pH 7.0 and 35 °C. The bioabatement of WS was performed by growing Coniochaeta ligniaria NRRL 30616 in the liquid portion of the pretreated WS aerobically at pH 6.5 and 30 °C for 15 h. The bacterium produced 21.6 ± 0.5 g
ethanol per liter in 40 h from the bioabated enzymatically saccharified WSH (total sugars, 44.1 ± 0.4 g) at pH 6.0. It produced
24.9 ± 0.3 g ethanol in 96 h and 26.7 ± 0.0 g ethanol in 72 h per liter from bioabated WSH by batch SSF and fed-batch SSF,
respectively. SSF offered a distinct advantage over SHF with respect to reducing total time required to produce ethanol from
the bioabated WS. Also, fed-batch SSF performed better than the batch SSF with respect to shortening the time requirement
and increase in ethanol yield. 相似文献
10.
The sequence of an endo-chitosanase gene ( CSN) from Aspergillus fumigatus was optimized based on the preferred codons of Pichia pastoris and synthesized in vitro through overlapping PCR ( CSN- P). The gene was cloned into a yeast expression vector, pHBM905A, and secretorily expressed in Pichia pastoris GS115. The yield of CSN-P reached ~3 mg/ml with a high-density fermentation in a 14 l fermenter and the enzyme activity was
~25,000 U/ml. The enzyme had half-lives of 2.5 h at 80°C, 1 h at 90°C and 32 min at 100°C. It retained 70% activity after
incubation with 10 M urea at room temperature for 30 min. This enzyme was used for a large-scale preparation of oligosaccharides:
3 g enzyme converted 200 kg chitosan into oligosaccharides in 24 h at 60°C. 相似文献
11.
Production of 2,3-butanediol by Bacillus subtilis takes place in late-log or stationary phase, depending on the expression of bdhA gene encoding acetoin reductase, which converts acetoin to 2,3-butanediol. The present work focuses on the development of
a strain of B. subtilis for enhanced production of 2,3-butanediol in early log phase of growth cycle. For this, the bdhA gene was expressed under the control of P
alsSD
promoter of AlsSD operon for acetoin fermentation which served the substrate for 2,3-butanediol production. Addition of acetic acid in the
medium induced the production of 2,3-butanediol by 2-fold. Two-step aerobic–anaerobic fermentation further enhanced 2,3-butanediol
production by 4-fold in comparison to the control parental strain. Thus, addition of acetic acid and low dissolved oxygen
in the medium are involved in activation of bdhA gene expression from P
alsSD
promoter in early log phase. Under the conditions tested in this work, the maximum production of 2,3-butanediol, 2.1 g/l
from 10 g/l glucose, was obtained at 24 h. Furthermore, under the optimized microaerophilic condition, the production of 2,3-butanediol
improved up to 6.1 g/l and overall productivity increased by 6.7-fold to 0.4 g/l h in the engineered strain compared to that
in the parental control. 相似文献
12.
Continuous production of fructooligosaccharides (FOS) by Aureobasidium pullulans immobilized on calcium alginate beads with a packed bed was investigated at a plant scale reactor. Optimum conditions were
with 770 g sucrose/l, being fed at 200 l/h at 50°C which gave a productivity of 180 g FOS/l h. Initial activity was maintained
for more than 100 days. The reactor was successfully scaled up to a production scale of 1.2 m 3. 相似文献
13.
We isolated and characterized a d-lactic acid-producing lactic acid bacterium ( d-LAB), identified as Lactobacillus delbrueckii subsp. lactis QU 41. When compared to Lactobacillus coryniformis subsp. torquens JCM 1166 T and L. delbrueckii subsp. lactis JCM 1248 T, which are also known as d-LAB, the QU 41 strain exhibited a high thermotolerance and produced d-lactic acid at temperatures of 50 °C and higher. In order to optimize the culture conditions of the QU 41 strain, we examined
the effects of pH control, temperature, neutralizing reagent, and initial glucose concentration on d-lactic acid production in batch cultures. It was found that the optimal production of 20.1 g/l d-lactic acid was acquired with high optical purity (>99.9% of d-lactic acid) in a pH 6.0-controlled batch culture, by adding ammonium hydroxide as a neutralizing reagent, at 43 °C in MRS
medium containing 20 g/l glucose. As a result of product inhibition and low cell density, continuous cultures were investigated
using a microfiltration membrane module to recycle flow-through cells in order to improve d-lactic acid productivity. At a dilution rate of 0.87 h −1, the high cell density continuous culture exhibited the highest d-lactic acid productivity of 18.0 g/l/h with a high yield (ca. 1.0 g/g consumed glucose) and a low residual glucose (<0.1 g/l)
in comparison with systems published to date. 相似文献
14.
Bagasse of Agave tequilana (BAT) is the residual lignocellulosic waste that remains from tequila production. In this study we characterized the chemical
composition of BAT, which was further saccharified and fermented to produce ethanol. BAT was constituted by cellulose (42%),
hemicellulose (20%), lignin (15%), and other (23%). Saccharification of BAT was carried out at 147°C with 2% sulfuric acid
for 15 min, yielding 25.8 g/l of fermentable sugars, corresponding to 36.1% of saccharificable material (cellulose and hemicellulose
contents, w/w). The remaining lignocellulosic material was further hydrolyzed by commercial enzymes, ~8.2% of BAT load was
incubated for 72 h at 40°C rendering 41 g/l of fermentable sugars corresponding to 73.6% of the saccharificable material (w/w).
Mathematic surface response analysis of the acid and enzymatic BAT hydrolysis was used for process optimization. The results
showed a satisfactory correlation ( R
2 = 0.90) between the obtained and predicted responses. The native yeast Pichia caribbica UM-5 was used to ferment sugar liquors from both acid and enzymatic hydrolysis to ethanol yielding 50 and 87%, respectively.
The final optimized process generated 8.99 g ethanol/50 g of BAT, corresponding to an overall 56.75% of theoretical ethanol
(w/w). Thus, BAT may be employed as a lignocellulosic raw material for bioethanol production and can contribute to BAT residue
elimination from environment. 相似文献
15.
The Aspergillus niger feruloyl esterase gene ( faeA) was cloned into Saccharomyces cerevisiae via a yeast expression vector, resulting in efficient expression and secretion of the enzyme in the medium with a yield of
~2 mg/l. The recombinant enzyme was purified to homogeneity by anion-exchange and hydrophobic interaction chromatography.
The specific activity was determined to be 8,200 U/μg (pH 6.5, 20°C, 3.5 mM 4-nitrophenyl ferulate). The protein had a correct
N-terminal sequence of ASTQGISEDLY, indicating that the signal peptide was properly processed. The FAE exhibited an optimum
pH of 6–7 and operated optimally at 50°C using ground switchgrass as the substrate. The yeast clone was demonstrated to catalyze
the release of ferulic acid continuously from switchgrass in YNB medium at 30°C. This work represents the first report on
engineering yeast for the breakdown of ferulic acid crosslink to facilitate consolidated bioprocessing. 相似文献
16.
A pilot plant for hydrothermal treatment of wheat straw was compared in reactor systems of two steps (first, 80°C; second,
190–205°C) and of three steps (first, 80°C; second, 170–180°C; third, 195°C). Fermentation (SSF) with Sacharomyces cerevisiae of the pretreated fibers and hydrolysate from the two-step system gave higher ethanol yield (64–75%) than that obtained from
the three-step system (61–65%), due to higher enzymatic cellulose convertibility. At the optimal conditions (two steps, 195°C
for 6 min), 69% of available C6-sugar could be fermented into ethanol with a high hemicellulose recovery (65%). The concentration
of furfural obtained during the pretreatment process increased versus temperature from 50 mg/l at 190°C to 1,200 mg/l at 205°C
as a result of xylose degradation. S. cerevisiae detoxified the hydrolysates by degradation of several toxic compounds such as 90–99% furfural and 80–100% phenolic aldehydes,
which extended the lag phase to 5 h. Acetic acid concentration increased by 0.2–1 g/l during enzymatic hydrolysis and 0–3.4 g/l
during fermentation due to hydrolysis of acetyl groups and minor xylose degradation. Formic acid concentration increased by
0.5–1.5 g/l probably due to degradation of furfural. Phenolic aldehydes were oxidized to the corresponding acids during fermentation
reducing the inhibition level. 相似文献
17.
Survival of two Lactobacillus kefir strains after spray drying in reconstituted skim milk with or without the addition of 12.5 g monosodium glutamate/l, 20 g
sucrose/l, or 20 g fructo-oligosaccharides (FOS)/l and during subsequent storage under different conditions of temperature
(20 and 30°C) and relative humidity (RH) (0, 11 and 23%) was evaluated. After being dried, L. kefir 8321 and L. kefir 8348 had a decrease in viability of 0.29 and 0.70 log cfu/ml respectively, while the addition of different protectants improved
the survival of both strains significantly. During storage, bacterial survival was significantly higher under lower conditions
of RH (0–11%), and monosodium glutamate and FOS proved to be the best protectants. 相似文献
18.
In this paper, in order to obtain some industrial strains with high yield of l-(+)-lactic acid, the wild type strain Lactobacillus casei CICC6028 was mutated by nitrogen ions implantation. By study, it was found that the high positive mutation rate was obtained
when the output power was 10 keV and the dose of N + implantation was 50 × 2.6 × 10 13 ions/cm 2. In addition, the initial screening methods were also studied, and it was found that the transparent halos method was unavailable,
for some high yield strains of l-(+)-lactic acid were missed. Then a mutant strain which was named as N-2 was isolated, its optimum fermentation temperature was 40°C and the l-(+)-lactic acid yield was 136 g/l compared to the original strain whose optimum fermentation temperature was 34°C and l-(+)-lactic acid production was 98 g/l. Finally, High Performance Liquid Chromatography method was used to analyze the purity
of l-(+)-lactic acid that was produced by the mutant N-2, and the result showed the main production of N-2 was l-(+)-lactic acid. 相似文献
19.
Ten species of Aspergillus isolated from soil samples collected from different locations in the Indian Himalayan region have been studied for their
growth requirements and tricalcium phosphate solubilization at different temperatures. The Aspergillus species could grow at low temperature and tolerated a wide range of pH. Phosphate solubilization by various Aspergillus species ranged between 374 μg/ml ( A. candidus) to 1394 μg/ml ( A. niger) at 28°C, 33 μg/ml ( A. fumigatus) to 2354 μg/ml ( A. niger) at 21°C, 93 μg/ml ( A. fumigatus) to 1452 μg/ml ( A. niger) at 14°C, and 21 μg/ml ( A. wentii) to 83 μg/ml ( A. niger) at 9°C. At 21 and 28°C, phosphate solubilization showed a decrease within 4 weeks of incubation, whereas at 9°C and 14°C,
it continued further up to 6 weeks of incubation. In general, phosphate solubilization by different Aspergillus species was recorded at a maximum of 28°C or 21°C; biomass production was favored at 21°C or 14°C. Conversely, A. nidulans and A. sydowii exhibited maximum phosphate solubilization at 14°C and produced maximum biomass at 21°C. Data suggest that suboptimal conditions
(higher or lower temperature) for fungal growth and biomass production were optimal for the production of metabolites involved
in phosphate solubilization. Significant negative correlations were obtained between pH and phosphate solubilization for eight
species at 28°C, for seven at 21°C, and for nine at 14°C. Extracellular phosphatase activity was exhibited only in case of
A. niger, whreas intracellular phosphatase activity was detected in all species, the maximum being in A. niger. Statistically significant positive or negative correlations were obtained between phosphate solubilization and other parameters
in most cases at different temperatures. 相似文献
20.
Traditional mycelium aging technology was improved to enhance arachidonic acid (ARA) production by Mortierella alpina ME-1. Filtration step was skipped and additional carbon and nitrogen sources were fed during aging. The levels of the significant
factors (time, temperature, ethanol, and KNO 3) affecting ARA production during improved aging process were also optimized by applying response surface methodology (RSM),
and the maximum ARA yield of 19.02 g/l was achieved in a 5 l fermentor at 5.6 days, temperature 13.7 °C, ethanol 42.44 g/l,
and KNO 3 2.62 g/l. This yield was 1.55 times higher than that of traditional aging technology. The improved mycelium aging technology
is considered to be a useful strategy for enhancing ARA production. 相似文献
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