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1.
P.I. Nikel M.C. Ramirez M.J. Pettinari B.S. Méndez M.A. Galvagno 《Journal of applied microbiology》2010,109(2):492-504
Aims: Analysis of the physiology and metabolism of Escherichia coli arcA and creC mutants expressing a bifunctional alcohol‐acetaldehyde dehydrogenase from Leuconostoc mesenteroides growing on glycerol under oxygen‐restricted conditions. The effect of an ldhA mutation and different growth medium modifications was also assessed. Methods and Results: Expression of adhE in E. coli CT1061 [arcA creC(Con)] resulted in a 1·4‐fold enhancement in ethanol synthesis. Significant amounts of lactate were produced during micro‐oxic cultures and strain CT1061LE, in which fermentative lactate dehydrogenase was deleted, produced up to 6·5 ± 0·3 g l?1 ethanol in 48 h. Escherichia coli CT1061LE derivatives resistant to >25 g l?1 ethanol were obtained by metabolic evolution. Pyruvate and acetaldehyde addition significantly increased both biomass and ethanol concentrations, probably by overcoming acetyl‐coenzyme A (CoA) shortage. Yeast extract also promoted growth and ethanol synthesis, and this positive effect was mainly attributable to its vitamin content. Two‐stage bioreactor cultures were conducted in a minimal medium containing 100 μg l?1 calcium d ‐pantothenate to evaluate oxic acetyl‐CoA synthesis followed by a switch into fermentative conditions. Ethanol reached 15·4 ± 0·9 g l?1 with a volumetric productivity of 0·34 ± 0·02 g l?1 h?1. Conclusions: Escherichia coli responded to adhE over‐expression by funnelling carbon and reducing equivalents into a highly reduced metabolite, ethanol. Acetyl‐CoA played a key role in micro‐oxic ethanol synthesis and growth. Significance and Impact of the Study: Insight into the micro‐oxic metabolism of E. coli growing on glycerol is essential for the development of efficient industrial processes for reduced biochemicals production from this substrate, with special relevance to biofuels synthesis. 相似文献
2.
A. Schäfer M. A. Stein K.-H. Schneider F. Giffhorn 《Applied microbiology and biotechnology》1997,48(1):47-52
By polymerase chain reaction mutagenesis techniques, an NdeI restriction site was introduced at the initiation codon of the mannitol dehydrogenase (MDH) gene (mtlK) of Rhodobacter sphaeroides Si4. The mtlK gene was then subcloned from plasmid pAK74 into the NdeI site of the overexpression vector pET24a+ to give plasmid pASFG1. Plasmid pASFG1 was introduced into Escherichia coli BL21(DE3), which was grown in a 1.5-l bioreactor at 37 °C and pH 7.0. Overexpression of MDH in Escherichia coli BL21(DE3) [pASFG1] was determined by enzymatic analysis and sodium dodecyl sulfate (SDS)/polyacrylamide gel electrophoresis.
Under standard growth conditions, E. coli produced considerable amounts of a polypeptide that correlated with MDH in SDS gels, but the activity yield was low. Decreasing
the growth temperature to 27 °C and omitting pH regulation resulted in a significant increase in the formation of soluble
and enzymatically active MDH up to a specific activity of 12.4 U/mg protein and a yield of 26 000 U/l, which corresponds to
0.38 g/l MDH. This was an 87-fold overexpression of MDH compared to that of the natural host R. sphaeroides Si4, and a 236-fold improvement of the volumetric yield. MDH was purified from E. coli BL21(DE3) [pASFG1] with 67% recovery, using ammo-nium sulfate precipitation, hydrophobic interaction chromatography, and
gel filtration. Partial characterization of the recombinant MDH revealed no significant differences to the wild-type enzyme.
Received: 18 February 1997 / Received revision: 27 March 1997 / Accepted: 27 March 1997 相似文献
3.
A food-grade vector system was developed that allows stable integration of multiple plasmid copies in the chromosome of Lactococcus lactis. The vector consists of the plus origin of replication (Ori+) of the lactococcal plasmid pWV01, the sucrose genes of the lactic acid bacterium Pediococcus pentosaceus PPE1.0 as selectable marker, a multiple-cloning site, and a lactococcal DNA fragment of a well-characterized chromosomal
region. The system includes two L. lactis strains, LL108 and LL302, which produce the pWV01 RepA protein essential for replication of the Ori+ vectors. These helper strains allow the construction and isolation of the replicating form of the integration plasmids from
a homologous background. Single-cross-over integration of the plasmids in L. lactis MG1363 resulted in amplifications to a level of approximately 20 copies/chromosome after selection of the transformants on
medium containing sucrose as the only fermentable sugar. The amplifications were stable under selective growth conditions.
In glucose-containing medium a limited loss of integrated plasmid copies was detected at a rate of (7.5–15) × 10−2 copies per generation. One strain, MG124, was isolated that had retained 11 integrated copies after a period of 120 generations
of non-selective growth. These results show that the single-cross-over integration system described here represents a simple
procedure for the engineering of stable food-grade strains carrying multiple copies of a gene of interest.
Received: 23 September 1997 / Received revision: 21 November 1997 / Accepted: 21 November 1997 相似文献
4.
Ingrid Sumeri Liisa Arike Jelena Stekolštšikova Riin Uusna Signe Adamberg Kaarel Adamberg Toomas Paalme 《Applied microbiology and biotechnology》2010,86(6):1925-1931
The effect of stress pretreatment on survival of probiotic Lactobacillus acidophilus La-5, Lactobacillus rhamnosus GG, and Lactobacillus fermentum ME-3 cultures was investigated in the single bioreactor gastrointestinal tract simulator (GITS). The cultures were pregrown
in pH-auxostat, subjected to temperature, acid, or bile stress treatment, fast frozen in liquid nitrogen (LN2), and tested for survival in GITS. After LN2 freezing the colony forming ability of L. rhamnosus GG and L. fermentum ME-3 nonstressed and stressed cells was well retained (average survival of 75.4 ± 18.3% and 88.0 ± 7.2%, respectively). L. acidophilus La-5 strain showed good survival of auxostat nonstressed cells after fast freezing (94.2 ± 15.0), however the survival of
stress pretreated cells was considerably lower (30.8 ± 8.5%). All LN2 frozen auxostat cultures survived well in the acid phase of the GIT simulation (survival 81 ± 21%); however, after the bile
phase, the colony formation ability of L. acidophilus La-5, L. rhamnosus GG, and L. fermentum ME-3 decreased by approximately 1.4 ± 0.2, 3.8 ± 0.3, and 3.5 ± 1.2 logarithmic units, respectively. No statistically relevant
positive effect of stress pretreatments on survival of LN2 frozen L. acidophilus La-5, L. rhamnosus GG, and L. fermentum ME-3 in GITS was observed. 相似文献
5.
Kuo-Hsing Lin Mei-Fang Chien Ju-Liang Hsieh Chieh-Chen Huang 《Applied microbiology and biotechnology》2010,87(2):561-569
Recombinant tilapia (Oreochromis mossambicus) fish metallothionein (MT) was used as a surface biosorbent for mercury removal in Escherichia coli. Fish MT conferred better resistance than did mouse or human MT. When tilapia MT (tMT) was fused with an outer-membrane protein,
outer membrane protein C (OmpC), the membrane-targeted fusion protein, OmpC–tMT, gave enhanced resistance compared with cytoplasmic
tMT expressed in the same host cell. The cytoplasmically expressed tMT showed high mercury adsorption (4.3 ± 0.4 mg/g cell
dry weight). The cell surface that expressed E. coli showed about 25% higher adsorption ability (5.6 ± 0.4 mg/g) than the cells expressing cytoplasmic MT, attaining almost twice
the level of adsorption of the control plasmid (3.0 ± 0.4 mg/g). As MTs are also known for their ability to scavenge hydroxyl-free
radicals, it was also shown that tMT exhibited better radical-scavenging activities than glutathione. These results suggest
that fish MT has potential for the development of a bioremediation system for mercury removal that protects the harboring
E. coli host by free-radical scavenging. 相似文献
6.
Nicola D’Amelio Luca Fontanive Fulvio Uggeri Furio Suggi-Liverani Luciano Navarini 《Food biophysics》2009,4(4):321-330
Caffeine complexation by chlorogenic acid (3-caffeoylquinic acid, CAS Number [327-97-9]) in aqueous solution as well as caffeine–chlorogenate
complex in freshly prepared coffee brews have been investigated by high-resolution 1H-NMR. Caffeine and chlorogenic acid self-associations have also been studied and self-association constants have been determined
resorting to both classical isodesmic model and a recently introduced method of data analysis able to provide also the critical
aggregation concentration (cac). Furthermore, caffeine–chlorogenate association constant was measured. For the caffeine, the
average value of the self-association constant determined by isodesmic model (K
i = 7.6 ± 0.5 M−1) is in good agreement with the average value (K
a = 10 ± 1.8 M−1) determined with the method which permits the determination of the cac (8.43 ± 0.05 mM). Chlorogenic acid shows a slight
decreased tendency to aggregation with a lower average value of association constants (K
i = 2.8 ± 0.6 M−1; K
a = 3.4 ± 0.6 M−1) and a critical concentration equal to 24 ± 1 mM. The value of the association constant of the caffeine–chlorogenate complex
(30 ± 4 M−1) is compatible with previous studies and within the typical range of reported association constants for other caffeine–polyphenol
complexes. Structural features of the complex have also been investigated, and the complex conformation has been rediscussed.
Caffeine chemical shifts comparison (monomeric, complexed, coffee brews) clearly indicates a significant amount of caffeine
is complexed in beverage real system, being chlorogenate ions the main complexing agents. 相似文献
7.
Ribitsch D Karl W Wehrschütz-Sigl E Tutz S Remler P Weber HJ Gruber K Stehr R Bessler C Hoven N Sauter K Maurer KH Schwab H 《Applied microbiology and biotechnology》2009,81(5):875-886
In the course of a microbial screening of soil samples for new oxidases, different enrichment strategies were carried out.
With choline as the only carbon source, a microorganism was isolated and identified as Arthrobacter nicotianae. From this strain, a gene coding for a choline oxidase was isolated from chromosomal DNA. This gene named codA was cloned in Escherichia coli BL21-Gold and the protein (An_CodA) heterologously overexpressed as a soluble intracellular protein of 59.1 kDa. Basic biochemical characterization of
purified protein revealed a pH optimum of 7.4 and activity over a broad temperature range (15–70 °C). Specific activities
were determined toward choline chloride (4.70 ± 0.12 U/mg) and the synthetic analogs bis(2-hydroxyethyl)-dimethylammonium
chloride (0.05 ± 0.45 × 10–2 U/mg) and tris-(2-hydroxyethyl)-methylammonium methylsulfate (0.01 ± 0.12 × 10–2 U/mg). With increasing number of oxidizable groups, a significant decrease in activity was noted. Determination of kinetic
parameters in atmorspheric oxygen resulted in K
M = 1.51 ± 0.09 mM and V
max = 42.73 ± 0.42 mU/min for choline chloride and K
M = 4.77 ± 0.76 mM and V
max = 48.40 ± 2.88 mU/min for the reaction intermediate betaine aldehyde respectively. Nuclear magnetic resonance spectroscopic
analysis of the products formed during the enzyme reaction with choline chloride showed that in vitro the intermediate betaine
aldehyde exists also free in solution. 相似文献
8.
Priya R Tadwal VS Roessle MW Gayen S Hunke C Peng WC Torres J Grüber G 《Journal of bioenergetics and biomembranes》2008,40(4):245-255
The first low resolution solution structure of the soluble domain of subunit b (b
22–156) of the Escherichia coli F1FO ATPsynthase was determined from small-angle X-ray scattering data. The dimeric protein has a boomerang-like shape with a
total length of 16.2 ± 0.3 nm. Fluorescence correlation spectroscopy (FCS) shows that the protein binds effectively to the
subunit δ, confirming their described neighborhood. Using the recombinant C-terminal domain (δ91–177) of subunit δ and the C-terminal peptides of subunit b, b
120–140 and b
140–156, FCS titration experiments were performed to assign the segments involved in δ–b assembly. These data identify the very C-terminal tail b
140–156 to interact with δ91–177. The novel 3D structure of this peptide has been determined by NMR spectroscopy. The molecule adopts a stable helix formation
in solution with a flexible tail between amino acid 140 to 145. 相似文献
9.
Mineralization of pentachlorophenol in a contaminated soil by Pseudomonas sp UG30 cells encapsulated in κ-carrageenan 总被引:2,自引:0,他引:2
M B Cassidy H Mullineers H Lee J T Trevors 《Journal of industrial microbiology & biotechnology》1997,18(1):43-48
A fermentation process in Escherichia coli for production of supercoiled plasmid DNA for use as a DNA vaccine was developed using an automated feed-back control nutrient
feeding strategy based on dissolved oxygen (DO) and pH. The process was further automated through a computer-aided data
processing system to regulate the cell growth rate by controlling interactively both the nutrient feed rate and agitation
speed based on DO. The process increased the total yield of the plasmid DNA by approximately 10-fold as compared to a manual
fed-batch culture. The final cell yield from the automated process reached 60 g L−1 of dry cell weight (OD600 = 120) within 24 h. A plasmid DNA yield of 100 mg L−1 (1.7 mg g−1 cell weight) was achieved by using an alkaline cell lysis method. Plasmid yield was confirmed using High Performance Liquid
Chromatography (HPLC) analysis. Because cells had been grown under carbon-limiting conditions in the automated process,
acetic acid production was minimal (below 0.01 g L−1) throughout the fed-batch stage. In contrast, in the manual process, an acid accumulation rate as high as 0.36 g L−1 was observed, presumably due to the high nutrient feed rates used to maintain a maximum growth rate. The manual fed-batch
process produced a low cell density averaging 10–12 g L−1 (OD600 = 25–30) and plasmid yields of 5–8 mg L−1 (approximately 0.7 mg g−1 cells). The improved plasmid DNA yields in the DO- and pH-based feed-back controlled process were assumed to be a result
of a combination of increased cell density, reduced growth rate (μ) from 0.69 h−1 to 0.13 h−1 and the carbon/nitrogen limitation in the fed-batch stage. The DO- and pH-based feed-back control, fed-batch process has
proven itself to be advantageous in regulating cell growth rate to achieve both high cell density and plasmid yield without
having to use pure oxygen. The process was reproducible in triplicate fermentations at both 7-L and 80-L scales.
Received 22 March 1996/ Accepted in revised form 20 September 1996 相似文献
10.
Influence of initial cellulose concentration on the carbon flow distribution during batch fermentation by Clostridium thermocellum ATCC 27405 总被引:1,自引:0,他引:1
The objective of this research was to understand how carbon loading influences hydrogen (H2) synthesis and metabolic flow patterns in the thermophilic, cellulolytic bacterium, Clostridium thermocellum. C. thermocellum was cultivated in batch cultures with high (5 g L−1) and low (1 g L−1) initial concentrations of α-cellulose at 60°C. The growth rate of C. thermocellum was 22% lower (0.15 h−1) in cultures with low-cellulose concentration compared with cultures with high-cellulose concentrations. Although substrate
depletion coincided with the end of log-growth in low-cellulose cultures, the prime reason for growth arrest in high-cellulose
cultures was not identified. Ethanol, acetate, and formate were the major soluble end-products with concomitant release of
H2 and CO2 under both conditions. Lactate appeared during the late log phase in high-carbon cultures when pH dropped below 6.4 and became
the major end-product in stationary phase. During the exponential phase of cell growth, significantly higher yields for H2 and acetate (1.90 ± 0.14 and 1.11 ± 0.04 mol/mol glucose equivalent, respectively) were obtained from low-cellulose cultures
compared to those from high-cellulose cultures. The maximum specific rate of H2 production, 6.41 ± 0.13 mmol H2/g dry cell/h, obtained during the exponential phase from low-carbon cultures was about 37% higher than that obtained from
high-carbon cultures. 相似文献
11.
The thermophilic bacterium, Thermus species ATCC 27978, which is capable of aerobically degrading benzene, toluene, ethylbenzene, and the xylenes (BTEX), was
cultured in 5-1 fermentors on a Castenholz salts-tryptone medium. This bacterium can be cultivated more conveniently at 45 °C,
a temperature substantially lower than its optimal growth temperature (approx. 60 °C). Yet, the washed harvested cells from
such cultures display the same initial BTEX-degrading activity as those when Thermus sp. is grown at its higher optimal temperature. Two bioreactor cultivation modes, batch and fed batch, were investigated.
More biomass and more BTEX-degrading activity (assayed at 60 °C) were generated in fed-batch cultures than in the growth-limited
batch cultures. The former yielded a biomass concentration of 2.5 g dry cell weight (DCW) l−1 and whole-cell degrading specific activities of 7.6 ± 1.3, 10.1 ± 1.9, 9.8 ± 2.1, 2.3 ± 0.5, and 4.6 ± 0.9 nmol degraded
(mg DCW)−1 min−1 for benzene, toluene, ethylbenzene, m-xylene, and the o- plus p-xylenes (unresolved mixture), respectively. Although the formation of cellular BTEX-degrading activity is growth-associated,
a slow to moderate specific growth rate of 0.02–0.07 h−1 favors the production of BTEX-degrading activity, while a high growth rate, of the order of 0.16 h−1, is detrimental to its production. The washed harvested Thermus sp. cells were capable of degrading BTEX over a broad range of thermophilic incubation temperatures, 45–77 °C.
Received: 28 June 1996 / Received revision: 31 December 1996 / Accepted: 31 January 1997 相似文献
12.
Dominic D. W. S. Wong Victor J. Chan Amanda A. McCormack Sarah B. Batt 《Applied microbiology and biotechnology》2010,86(5):1463-1471
A novel xyloglucan-specific endo-β-1,4-glucanase gene (xeg5A) was isolated, cloned, and expressed in Esherichia coli. The enzyme XEG5A consisted of a C-terminal catalytic domain and N-terminal sequence of ~90 amino acid residues with unknown
function. The catalytic domain assumed an (α/β)8-fold typical of glycoside hydrolase (GH) family 5, with the two catalytic residues Glu240 and Glu362 located on opposite
sides of the surface groove of the molecule. The recombinant enzyme showed high specificity towards tamarind xyloglucan and
decreasing activity towards xyloglucan oligosaccharide (HDP-XGO), carboxymethyl cellulose, and lichenan. Tamarind xyloglucan
was hydrolyzed to three major fragments, XXXG, XXLG/XLXG, and XLLG. The hydrolysis followed the Michaelis–Menten kinetics,
yielding K
m and V
max of 3.61 ± 0.23 mg/ml and 0.30 ± 0.01 mg/ml/min, respectively. However, the hydrolysis of HDP-XGO showed a decrease in the
rate at high concentrations suggesting appearance of excess substrate inhibition. The addition of XXXG resulted in linear
noncompetitive inhibition on the hydrolysis of tamarind xyloglucan giving a K
i of 1.46 ± 0.13 mM. The enzyme was devoid of transglycosylase activities. 相似文献
13.
The purpose of this work was to develop and optimize gliclazide-loaded alginate–methyl cellulose mucoadhesive microcapsules
by ionotropic gelation using central composite design. The effect of formulation parameters like polymer blend ratio and cross-linker
(CaCl2) concentration on properties of gliclazide-loaded alginate–methyl cellulose microcapsules like drug encapsulation efficiency
and drug release were optimized. The optimized microcapsules were subjected to swelling, mucoadhesive, and in vivo studies. The observed responses coincided well with the predicted values from the optimization technique. The optimized microcapsules
showed high drug encapsulation efficiency (83.57 ± 2.59% to 85.52 ± 3.07%) with low T
50% (time for 50% drug release, 5.68 ± 0.09 to 5.83 ± 0.11 h). The in vitro drug release pattern from optimized microcapsules was found to be controlled-release pattern (zero order) with case II transport
release mechanism. Particle sizes of these optimized microcapsules were 0.767 ± 0.085 to 0.937 ± 0.086 mm. These microcapsules
also exhibited good mucoadhesive properties. The in vivo studies on alloxan-induced diabetic rats indicated the significant hypoglycemic effect that was observed 12 h after oral
administration of optimized mucoadhesive microcapsules. The developed and optimized alginate–methyl cellulose microcapsules
are suitable for prolonged systemic absorption of gliclazide to maintain lower blood glucose level and improved patient compliance. 相似文献
14.
Hendrik Schewe Dirk Holtmann Jens Schrader 《Applied microbiology and biotechnology》2009,83(5):849-857
A recombinant Escherichia coli BL21 (DE3) strain overexpressing a variant of P450BM-3 (V26T/R47F/A74G/F87V/L188K; abbreviated: BL21 (P450BM-3 QM)) oxyfunctionalizes the bicyclic monoterpene α-pinene to α-pinene oxide, verbenol, and myrtenol. To address the low water
solubility and the toxicity of terpenoids, an aqueous–organic two-phase bioprocess was developed. Diisononyl phthalate was
selected as a biocompatible organic carrier solvent capable of masking the toxic effects mediated by α-pinene and of efficiently
extracting the products enabling scale-up to the bioreactor. With an aqueous to organic phase ratio of 3:2 and 30% (v/v) of α-pinene in the organic phase, a biocatalytic product formation period of more than 4 h was achieved. A comparison of
the biotransformation performance of BL21 (P450BM-3 QM) and a strain with an additional heterologous NADPH regeneration system comprising glucose facilitator and dehydrogenase,
but only expressing half the amount of P450BM-3 QM, shows comparable product concentrations of 1,020 ± 144 and 800 ± 61 mg lAq−1, respectively. The total product yields Y
P/P450 (μmol μmolP450−1) were 80% higher when the strain with the cofactor regeneration system was used. A total product concentration of over 1 g
lAq−1, corresponding to the highest value reported for microbial α-pinene oxyfunctionalization so far, marks a promising step forward
toward a future application of recombinant microorganisms for the selective oxidation of terpenoids to value-added products. 相似文献
15.
J. B. K. Leonard J. F. Norieka B. Kynard S. D. McCormick 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(4-5):287-295
To assess the energetics of migration in an anadromous fish, adult American shad (Alosa sapidissima) were swum in a large respirometer at a range of speeds (1.0–2.3 body lengths (BL) s−1, 13–24 °C). Metabolic rate (MO2) was logarithmically related to swimming speed (Bl s−1; r
2 = 0.41, slope = 0.23 ± 0.037) and tailbeat frequency (beats × min−1; r
2 = 0.52, slope = 0.003 ± 0.0003). Temperature had a significant effect on metabolic rate (r
2 = 0.41) with a Q10 of 2.2. Standard metabolic rate (SMR), determined directly after immobilization with the neuroblocker gallamine triethiodide,
ranged from 2.2–6.2 mmolO2 kg−1 h−1 and scaled with mass (W) such that SMR = 4.0 (±0.03)W0.695(±0.15). Comparison of directly determined and extrapolated SMR suggests that swimming respirometry provides a good estimate of SMR
in this species, given the differences in basal activity monitored by the two methods. Overall, American shad metabolic rates
(MO2 and SMR) were intermediate between salmonids and fast-swimming perciforms, including tunas, and may be a result of evolutionary
adaptation to their active pelagic, schooling life history. This study demonstrates variability in metabolic strategy among
anadromous fishes that may be important to understanding the relative success of different migratory species under varying
environmental conditions.
Accepted: 3 March 1999 相似文献
16.
An DS Cui CH Sung BH Yang HC Kim SC Lee ST Im WT Kim SG 《Applied microbiology and biotechnology》2012,94(3):673-682
The gene encoding an α-l-arabinofuranosidase that could biotransform ginsenoside Rc {3-O-[β-d-glucopyranosyl-(1–2)-β-d-glucopyranosyl]-20-O-[α-l-arabinofuranosyl-(1–6)-β-d-glucopyranosyl]-20(S)-protopanaxadiol} to ginsenoside Rd {3-O-[β-d-glucopyranosyl-(1–2)-β-d-glucopyranosyl]-20-O-β-d-glucopyranosyl-20(S)-protopanaxadiol} was cloned from a soil bacterium, Rhodanobacter ginsenosidimutans strain Gsoil 3054T, and the recombinant enzyme was characterized. The enzyme (AbfA) hydrolyzed the arabinofuranosyl moiety from ginsenoside
Rc and was classified as a family 51 glycoside hydrolase based on amino acid sequence analysis. Recombinant AbfA expressed
in Escherichia coli hydrolyzed non-reducing arabinofuranoside moieties with apparent K
m values of 0.53 ± 0.07 and 0.30 ± 0.07 mM and V
max values of 27.1 ± 1.7 and 49.6 ± 4.1 μmol min−1 mg−1 of protein for p-nitrophenyl-α-l-arabinofuranoside and ginsenoside Rc, respectively. The enzyme exhibited preferential substrate specificity of the exo-type
mode of action towards polyarabinosides or oligoarabinosides. AbfA demonstrated substrate-specific activity for the bioconversion
of ginsenosides, as it hydrolyzed only arabinofuranoside moieties from ginsenoside Rc and its derivatives, and not other sugar
groups. These results are the first report of a glycoside hydrolase family 51 α-l-arabinofuranosidase that can transform ginsenoside Rc to Rd. 相似文献
17.
Daisuke Sugimori 《Applied microbiology and biotechnology》2009,82(2):351-357
To develop a microbial treatment of edible oil-contaminated wastewater, microorganisms capable of rapidly degrading edible
oil were screened. The screening study yielded a yeast coculture comprising Rhodotorula pacifica strain ST3411 and Cryptococcus laurentii strain ST3412. The coculture was able to degrade efficiently even at low contents of nitrogen ([NH4–N] = 240 mg/L) and phosphorus sources ([PO4–P] = 90 mg/L). The 24-h degradation rate of 3,000 ppm mixed oils (salad oil/lard/beef tallow, 1:1 w/w) at 20°C was 39.8% ± 9.9% (means ± standard deviations of eight replicates). The highest degradation rate was observed at
20°C and pH 8. In a scaled-up experiment, the salad oil was rapidly degraded by the coculture from 671 ± 52.0 to 143 ± 96.7 ppm
in 24 h, and the degradation rate was 79.4% ± 13.8% (means ± standard deviations of three replicates). In addition, a repetitive
degradation was observed with the cell growth by only pH adjustment without addition of the cells. 相似文献
18.
This study compares the thermal ecology of male bearded dragon lizards (Pogona barbata) from south-east Queensland across two seasons: summer (1994–1995) and autumn (1995). Seasonal patterns of body temperature
(T
b) were explored in terms of changes in the physical properties of the thermal environment and thermoregulatory effort. To
quantify thermoregulatory effort, we compared behavioral and physiological variables recorded for observed lizards with those
estimated for a thermoconforming lizard. The study lizards' field T
bs varied seasonally (summer: grand daily mean (GDM) 34.6 ± 0.6°C, autumn: GDM 27.5 ± 0.3°C) as did maximum and minimum available
operative temperatures (summer: GDM T
max 42.1 ± 1.7°C, T
min 32.2 ± 1.0°C, autumn: GDM T
max 31.7 ± 1.2°C, T
min 26.4 ± 0.5°C). Interestingly, the range of temperatures that lizards selected in a gradient (selected range) did not change
seasonally. However, P. barbata thermoregulated more extensively and more accurately in summer than in autumn; lizards generally displayed behaviors affecting
heat load nonrandomly in summer and randomly in autumn, leading to the GDM of the mean deviations of lizards' field T
bs from their selected ranges being only 2.1 ± 0.5°C in summer, compared to 4.4 ± 0.5°C in autumn. This seasonal difference
was not a consequence of different heat availability in the two seasons, because the seasonally available ranges of operative
temperatures rarely precluded lizards from attaining field T
bs within their selected range, should that have been the goal. Rather, thermal microhabitat distribution and social behavior
appear to have had an important influence on seasonal levels of thermoregulatory effort.
Received: 28 April 1997 / Accepted: 29 December 1997 相似文献
19.
Raúl Muñoz María Hernández Ana Segura Joao Gouveia Antonia Rojas Juan Luis Ramos Santiago Villaverde 《Applied microbiology and biotechnology》2009,83(1):189-198
The long-term performance and stability of Pseudomonas putida mt-2 cultures, a toluene-sensitive strain harboring the genes responsible for toluene biodegradation in the archetypal plasmid
pWW0, was investigated in a chemostat bioreactor functioning under real case operating conditions. The process was operated
at a dilution rate of 0.1 h−1 under toluene loading rates of 259 ± 23 and 801 ± 78 g m−3 h−1 (inlet toluene concentrations of 3.5 and 10.9 g m−3, respectively). Despite the deleterious effects of toluene and its degradation intermediates, the phenotype of this sensitive
P. putida culture rapidly recovered from a 95% Tol− population at day 4 to approx. 100% Tol+ cells from day 13 onward, sustaining elimination capacities of 232 ± 10 g m−3 h−1 at 3.5 g Tol m−3 and 377 ± 13 g m−3 h−1 at 10.9 g Tol m−3, which were comparable to those achieved by highly tolerant strains such as P. putida DOT T1E and P. putida F1 under identical experimental conditions. Only one type of Tol− variant, harboring a TOL-like plasmid with a 38.5 kb deletion (containing the upper and meta operons for toluene biodegradation), was identified. 相似文献
20.
Contamination of foods with pathogens such as Escherichia coli O157:H7 and Salmonella is a major concern worldwide and rapid, sensitive, and reliable methods are needed for detection of these organisms. Since
these pathogens can contaminate similar foods and other types of samples, a multiplex polymerase chain reduction (PCR) was
designed to allow simultaneous detection of both E. coli O157:H7 and Salmonella spp directly from enrichment cultures. Samples of apple cider, beef carcass wash water, ground beef, and bovine feces were
inoculated with both E. coli O157:H7 and S. typhimurium at various bacterial levels. Following enrichment culturing for 20–24 h at 37°C in modified EC broth or buffered peptone
water both containing novobiocin, the samples were subjected to a DNA extraction technique or to immunomagnetic separation
then tested by the multiplex PCR assay. Four pairs of primers were employed in the PCR: primers for amplification of E. coli O157:H7 eaeA, stx
1/2 and plasmid sequences and for amplification of a portion of the Salmonella invA gene. Four fragments of the expected sizes were amplified in a single reaction and visualized following agarose gel electrophoresis
in all the samples inoculated with ≤ 1 CFU g−1 or ml−1. Results can be obtained in approximately 30 h. The multiplex PCR is a potentially powerful technique for rapid and sensitive
co-detection of both pathogens in foods and other types of samples.
Received 28 December 1997/ Accepted in revised form 19 March 1998 相似文献