| 1. |
- Mamo, Gashaw, et al.
(författare)
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Preface
- 2020
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Ingår i: Alkaliphiles in Biotechnology. - 0724-6145. ; 172
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Bisagni, Serena, et al.
(författare)
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Cloning and expression of a Baeyer-Villiger monooxygenase oxidizing linear aliphatic ketones from Dietzia sp. D5
- 2014
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Ingår i: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 109, s. 161-169
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Tidskriftsartikel (refereegranskat)abstract
- A Baeyer-Villiger monooxygenase has been identified in the genome sequence of Dietzia sp. D5. Sequence similarity search revealed that the enzyme belongs to a group of BVMOs that are closely related to ethionamide monooxygenase from Mycobacterium tuberculosis (EthA). The BVMO was expressed in E. coli BL21-CodonPlus(DE3)-RP and the best expression was achieved when the E. coli cells were cultivated in terrific broth (TB) at 15 degrees C and induced with 0.1 mM of IPTG. Since the purified enzyme did not show any measurable activity, the substrate scope of the BVMO has been determined using whole-cell and crude cell extract systems. The enzyme was most active towards linear aliphatic substrates. However, it has shown a moderate degree of conversion for cyclobutanone, 2-methylcyclohexanone, bicyclo[3.2.0]hept-2-en-6-one, phenylacetone and thioanisole. There was no detectable conversion of ethionamide, cyclohexanone and acetophenone. (C) 2014 Elsevier B.V. All rights reserved.
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| 3. |
- Bisagni, Serena, et al.
(författare)
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Cloning, expression and characterization of a versatile Baeyer-Villiger monooxygenase from Dietzia sp. D5.
- 2014
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Ingår i: AMB Express. - : Springer Science and Business Media LLC. - 2191-0855. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- A novel BVMO encoding gene was identified from a draft genome sequence of a newly isolated strain of Dietzia. Analysis of the protein sequence revealed that it belongs to a group of BVMOs whose most characterized member is cyclopentadecanone monooxygenase (CPDMO). The gene was PCR amplified, cloned and successfully expressed in E. coli. The expressed recombinant enzyme was purified using metal affinity chromatography. Characterization of the purified enzyme revealed that it has a broad substrate scope and oxidized different compounds including substituted and unsubstituted alicyclic, bicyclic-, aliphatic-ketones, ketones with an aromatic moiety, and sulfides. The highest activities were measured for 2- and 3-methylcyclohexanone, phenylacetone, bicyclo-[3.2.0]-hept-2-en-6-one and menthone. The enzyme was optimally active at pH 7.5 and 35°C, a temperature at which its half-life was about 20 hours. The stability studies have shown that this enzyme is more stable than all other reported BVMOs except the phenylacetone monooxygenase from the thermophilic organism Thermobifida fusca.
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| 4. |
- Bisagni, Serena, et al.
(författare)
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Exploring the Substrate Specificity and Enantioselectivity of a Baeyer-Villiger Monooxygenase from Dietzia sp D5: Oxidation of Sulfides and Aldehydes
- 2014
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 57:5, s. 366-375
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Tidskriftsartikel (refereegranskat)abstract
- Baeyer-Villiger monooxygenases (BVMOs) are valuable enzymes for specific oxyfunctionalization chemistry. They catalyze the oxidation of ketones to esters, but are also capable of oxidizing other chemical functions, namely aldehydes and heteroatoms such as sulfur, nitrogen, selenium and boron. The oxidation specificity and enantioselectivity of a newly characterized BVMO (BVMO4) from a strain of Dietzia towards sulfide- and aldehyde substrates have been studied. BVMO4 could react with sulfides containing an aromatic group. The presence of a substituent on the aromatic group was tolerated when they were in the meta- and para position and the oxidations yielded predominantly the (R)-sulfoxides. Similarly, BVMO4 displayed a higher activity for aldehydes containing a phenyl group, but long aliphatic aldehydes, namely octanal and decanal, were also accepted as substrate by this enzyme. The major oxidation products of the aldehyde substrates were the respective carboxylic acids in contrast to formate ester that was obtained in most of the previous reports. The Baeyer-Villiger oxidation of the substrate 2-phenylpropionaldehyde was studied in further detail and the corresponding acid product was obtained with good regio- and enantioselectivity. This is a unique feature for BVMO4 and is of great interest for further exploration of an alternative biocatalytic process.
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| 5. |
- Chávez, Georgina, et al.
(författare)
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Baeyer-Villiger Oxidation of Cyclohexanone in Aqueous Medium with In Situ Generation of Peracid Catalyzed by Perhydrolase CLEA
- 2014
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 57:5, s. 349-355
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Tidskriftsartikel (refereegranskat)abstract
- A perhydrolase, immobilized as a cross linked enzyme aggregate (CLEA), was employed to catalyze the in situ formation of peracetic acid (PAA) from ethylene glycol diacetate (EGDA) and hydrogen peroxide. The produced PAA was used for the Baeyer-Villiger oxidation of cyclohexanone, which afforded caprolactone in 63 % yield. The effect of type and amount of acyl donor, solvent, pH, temperature and ratio of cyclohexanone to hydrogen peroxide on the production of caprolactone was studied. The highest caprolactone yield was obtained with 100 mM EGDA as the acyl donor at pH 6 and room temperature using a ratio of cyclohexanone to hydrogen peroxide ratio of 1:4. Interestingly, the perhydrolase CLEA exhibited the highest activity in aqueous medium in contrast to the well studied lipase B from Candida antarctica. The perhydrolase CLEA proved to be a very efficient catalyst; the K (m) and V-max values were 118 mM and 56.3 mu mol min(-1), respectively.
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| 6. |
- Chávez, Georgina, et al.
(författare)
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Baeyer-Villiger oxidation with peracid generated in situ by CaLB-CLEA catalyzed perhydrolysis
- 2013
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Ingår i: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 89, s. 67-72
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Tidskriftsartikel (refereegranskat)abstract
- Candida antarctica lipase B, immobilized as cross linked enzyme aggregates (CLEAs) was used to mediate the Baeyer-Villiger oxidation of cyclohexanone to epsilon-caprolactone, and the reaction was compared with the one using Novozym (R) 435 as catalyst. The conversion was dependent on the initial concentration of cyclohexanone, and was about 90% after 48 h at concentrations of up to 0.25 M but was decreased at higher concentrations. Caprolactone concentrations up to 0.6 M had no effect on the reaction efficiency. Among the cyclic ketones tested, the highest degree of conversion was achieved for cyclopentanone (88%) and the lowest for cyclooctanone (about 2%). The effect of methyl substitution and position of substitution on the cycloketone was studied using methylcyclohexanone and it has shown to influence the conversion efficiency. Both hydrogen peroxide and the reaction by-product acetic acid had a deleterious effect on the stability of the biocatalyst. (C) 2012 Elsevier B.V. All rights reserved.
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| 7. |
- Danesh, Abolghasem, et al.
(författare)
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Production of haloduracin by Bacillus halodurans using solid-state fermentation.
- 2011
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Ingår i: Biotechnology Letters. - : Springer Science and Business Media LLC. - 1573-6776 .- 0141-5492. ; 33, s. 1339-1344
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Tidskriftsartikel (refereegranskat)abstract
- Bacillus halodurans was cultivated on wheat bran as a solid-state substrate and produced haloduracin, a bacteriocin, at about 245 AU per wheat bran. Supplementation of the bran with Lauria-Bertani broth decreased haloduracin production. However, production was stimulated by addition of Mg(2)SO(4) and K(2)HPO(4). The highest production was achieved at a wheat bran/moisture ratio of 1:1.8 and in the presence of 10% (w/w) Na(2)CO(3). Under optimum conditions, the organism produced about 3,000 AU per gram dry bran.
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| 8. |
- Doan Van, Thuoc, et al.
(författare)
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Ectoine-mediated protection of enzyme from the effect of pH and temperature stress: a study using Bacillus halodurans xylanase as a model.
- 2013
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 97:14, s. 6271-6278
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Tidskriftsartikel (refereegranskat)abstract
- Compatible solutes are small, soluble organic compounds that have the ability to stabilise proteins against various stress conditions. In this study, the protective effect of ectoines against pH stress is examined using a recombinant xylanase from Bacillus halodurans as a model. Ectoines improved the enzyme stability at low (4.5 and 5.0) and high pH (11 and 12); stabilisation effect of hydroxyectoine was superior to that of ectoine and trehalose. In the presence of hydroxyectoine, residual activity (after 10 h heating at 50 °C) increased from about 45 to 86 % at pH 5 and from 33 to 89 % at pH 12. When the xylanase was incubated at 65 °C for 5 h with 50 mM hydroxyectoine at pH 10, about 40 % of the original activity was retained while no residual activity was detected in the absence of additives or in the presence of ectoine or trehalose. The xylanase activity was slightly stimulated in the presence of 25 mM ectoines and then gradually decreased with increase in ectoines concentration. The thermal unfolding of the enzyme in the presence of the compatible solutes showed a modest increase in denaturation temperature but a larger increase in calorimetric enthalpy.
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| 9. |
- Doan Van, Thuoc, et al.
(författare)
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Utilization of agricultural residues for poly(3-hydroxybutyrate) production by Halomonas boliviensis LC1
- 2008
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Ingår i: Journal of Applied Microbiology. - : Oxford University Press (OUP). - 1364-5072 .- 1365-2672. ; 104:2, s. 420-428
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Utilization of cheap and readily available agricultural residues as cheap carbon sources for poly(3-hydroxybutyrate) (PHB) production by Halomonas boliviensis. Methods and results: Wheat bran was hydrolysed by a crude enzyme preparation from Aspergillus oryzae NM1 to provide a mixture of reducing sugars composed mainly of glucose, mannose, xylose and arabinose. Growth of H. boliviensis using a mixture of glucose (0.75% w/v) and xylose (0.25% w/v) in the medium led to a PHB content and concentration of 45 wt% and 1 g l(-1), respectively, after 30 h. A similar PHB concentration was attained when H. boliviensis was grown on wheat bran hydrolysate but with a lower PHB content, 34 wt%. In a batch cultivation mode in a fermentor, using 1.8% (w/v) reducing sugars, the maximum PHB accumulation by H. boliviensis was attained in 20 h, but was reduced to about 30 wt%. By adding butyric acid (0.8% v/v), sodium acetate (0.8% w/v) and decreasing the reducing sugars concentration to 1.0% w/v in the medium, PHB accumulation and concentration were increased to 50 wt% and 4 g l(-1), respectively, after 20 h. Butyric acid and sodium acetate for PHB production could also be provided by anaerobic digestion of solid potato waste. Conclusions: Cheap and readily available agricultural residues can be used as substrates to produce PHB. The production of PHB by H. boliviensis using wheat bran hydrolysate as source of carbon is expected to reduce the production cost and motivates further studies. Significance and Impact of the Study: Large-scale commercial utilization of PHB is mainly hampered by its high production cost. Carbon source for PHB production accounts up to 50% of the total production costs. Thus, the use of waste agricultural residues can substantially reduce the substrate cost (and in turn even provide value to the waste), and can downsize the production costs. This improves the market competitiveness. Studies on PHB production by moderate halophiles were recently initiated with H. boliviensis and findings show that it has potential for commercial exploitation. PHB production by H. boliviensis using wheat bran and potato waste is hence interesting.
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| 10. |
- Faryar, Reza, et al.
(författare)
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Production of prebiotic xylooligosaccharides from alkaline extracted wheat straw using the K80R-variant of a thermostable alkali-tolerant xylanase
- 2015
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Ingår i: Food and Bioproducts Processing. - : Elsevier BV. - 1744-3571 .- 0960-3085. ; 93:Online 22 November 2014, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Agricultural by-products are raw materials of importance for increased utilization of renewable biomass. Wheat straw is a raw material of significant production volume and is in this work used for production of xylooligosaccharides (XOS). Extraction of xylan by dilute alkali was followed by hydrolysis using a variant of the alkali-tolerant Bacillus halodurans S7 endoxylanase A mutated at K80R. The xylan yield was on average 56.5 g xylose equivalents per kg dried, ground wheat straw, with 1 arabinose per 12 xylose residues. The K80R variant, which displayed higher specific activity than the wild-type enzyme, was added at a load of 96 U/g extracted xylan. The XOS-yield (xylobiose – xylopentaose) was evaluated at time intervals in the temperature range of 50 to 65 degrees C, at pHs from 7 to 10. The enzyme was optimally active at 60 degrees C up to pH 9. Hydrolysis was completed within 7 h, resulting in 36 % conversion of the xylan to predominantly xylobiose. Xylose content was low (2.4%) despite extended incubation, which is desirable for XOS-production. The XOS-containing hydrolysate was confirmed as a suitable carbon source for the putative probiotic strain Lactobacillus brevis DSM 1269, showing the applicability of the method to obtain prebiotic XOS.
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