Whole-cell Gluconobacter oxydans biosensor for 2-phenylethanol biooxidation monitoring

A microbial biosensor for 2-phenylethanol (2-PE) based on the bacteria Gluconobacter oxydans was developed and applied in monitoring of a biotechnological process. The cells of G. oxydans were immobilized within a disposable polyelectrolyte complex gel membrane consisting of sodium alginate, cellulose sulphate and poly(methylene-co-guanidine) attached onto a miniaturized Clark oxygen electrode, forming whole cell amperometric biosensor. Measured changes in oxygen concentration were proportional to changes in 2-PE concentration. The biosensor sensitivity was 864 nA mM⁻¹ (RSD = 6%), a detection limit of 1 μM, and the biosensor response towards 2-PE was linear in the range 0.02–0.70 mM. The biosensor preserved 93% of its initial sensitivity after 7 h of continuous operation and exhibited excellent storage stability with loss of only 6% of initial sensitivity within two months, when stored at 4 °C. The developed system was designed and successfully used for an off-line monitoring of whole course of 2-PE biooxidation process producing phenylacetic acid (PA) as industrially valuable aromatic compound. The biosensor measurement did not require the use of hazardous organic solvent. The biosensor response to 2-PE was not affected by interferences from PA and phenylacetaldehyde at concentrations present in real samples during the biotransformation and the results were in a very good agreement with those obtained via gas chromatography.     

Immobilization in biotechnology and biorecognition: from macro- to nanoscale systems

Biological molecules such as enzymes, cells, antibodies, lectins, peptide aptamers, and cellular components in an immobilized form are extensively used in biotechnology, in biorecognition and in many medicinal applications. This review provides a comprehensive summary of the developments in new immobilization materials, techniques, and their practical applications previously developed by the authors. A detailed overview of several immobilization materials and technologies is given here, including bead cellulose, encapsulation in ionotropic gels and polyelectrolyte complexes, and various immobilization protocols applied onto surfaces. In addition, the review summarises the screening and design of an immobilization protocol, practical applications of immobilized biocatalysts in the industrial production of metabolites, monitoring, and control of fermentation processes, preparation of electrochemical/optical biosensors and biofuel cells.     

Annealing of gold nanoparticles on GaP(111)B: initial stage of GaP nanowire growth

GaP(111)B substrate was strewn with 30 nm colloidal Au nanoparticles. Organic residues were removed by: A) boiling in acetone and isopropylalcohol followed by a DI water rinse, B) treatment A + HF:H₂O, C) treatment A + O₂ plasma for 10 min, 20 min, and 40 min, and D) treatment A combined with O₂ plasma (10 min) and HF:H₂O. The substrate thus had original ‘epi‐ready' oxides (A), or fresh native oxides (B and D), or new added oxides (C). The samples were annealed at T_a = 650 °C for 10 min under PH₃ and H₂ in an MOVPE chamber. This resulted in the growth of GaP stumps along [111]B on each sample. Their length was <3 nm (B and D), ～20 nm (A), and ～220 nm (C 40 min). Elemental Ga is left as P₂O₅/Ga₂O₃ oxides form on etched GaP(111)B at room temperature. We believe that as the oxides disintegrated during annealing, they released the elemental Ga that combined with phosphorus from PH₃, and this led to the growth of the GaP stumps. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Envelopes of syndetic subsemigroups of the acting topological semigroup in a semiflow

A theory of semiflows with a discrete acting topological semigroup was developed in the 2000 paper by D. Ellis, R. Ellis and M. Nerurkar (2000) [3]. A theory for the case of an arbitrary acting topological semigroup has still to be developed. This paper can be considered as the beginning of an attempt in that direction.We introduce the notion of the envelope of a g-syndetic subsemigroup of the acting topological semigroup in a semiflow and prove various properties of this notion. We give some examples and deduce some statements from other papers as corollaries of our statements.     

Enzymatic Oxidation and Separation of Various Saccharides with Immobilized Glucose Oxidase

Glucose oxidase from Aspergillus niger, the specific enzyme for β-d-glucose oxidation, can also oxidize other related saccharides at very slow or negligible rates. The present study aimed to compare the kinetics of d-glucose oxidation using immobilized glucose oxidase on bead cellulose for the oxidation of related saccharides using the same biocatalyst. The significant differences were observed between the reaction rates for d-glucose and other saccharides examined. As a result, k _cat/K _M ratio for d-glucose was determined to be 42 times higher than d-mannose, 61.6 times higher than d-galactose, 279 times higher than d-xylose, and 254 times higher than for d-fructose and d-cellobiose. On the basis of these differences, the ability of immobilized glucose oxidase to remove d-glucose from d-cellobiose, d-glucose from d-xylose, and d-xylose from d-lyxose was examined. Immobilized catalase on Eupergit and mixed with immobilized glucose oxidase on bead cellulose or co-immobilized with glucose oxidase on bead cellulose was used for elimination of hydrogen peroxide from the reaction mixture. The accelerated elimination of d-glucose and d-xylose in the presence of co-immobilized catalase was observed. The co-immobilized glucose oxidase and catalase were able to decrease d-glucose or d-xylose content to 0–0.005% of their initial concentrations, while a minimum decrease of low oxidized saccharides d-xylose, d-cellobiose, and d-lyxose, respectively, was observed.     

Indecomposability and Devaney’s chaoticity of semiflows with an arbitrary acting abelian topological semigroup

We prove that a semiflow with an arbitrary acting abelian topological semigroup is Devaney chaotic if and only if it is nonminimal, indecomposable and has a dense set of periodic points. This generalizes a result of X. Wang and Y. Huang.     

A Relation Between Almost Automorphic and Levitan Almost Periodic Points in Compact Minimal Flows

We establish relations between the notions of almost automorphic, Levitan almost periodic and regularly almost periodic points in compact minimal flows for the case of the acting groups whose all continuous characters have syndetic kernels. In particular, we generalize and give a new proof of a theorem by Bronstein.      

Comparison of different technologies for alginate beads production

This paper describes the results of the round robin experiment “Bead production technologies” carried out during the COST 840 action “Bioencapsulation Innovation and Technologies” within the 5th Framework Program of the European Community. In this round robin experiment, calcium alginate hydrogel beads with the diameter of (800 ± 100) μm were produced by the most common bead production technologies using 0.5–4 mass % sodium alginate solutions as starting material. Dynamic viscosity of the alginate solutions ranged from less than 50 mPa s up to more than 10000 mPa s. With the coaxial air-flow and electrostatic enhanced dropping technologies as well as with the JetCutter technology in the soft-landing mode, beads were produced from all alginate solutions, whereas the vibration technology was not capable to process the high-viscosity 3 % and 4 % alginate solutions. Spherical beads were generated by the electrostatic and the JetCutter technologies. Slightly deformed beads were obtained from high-viscosity alginate solutions using the coaxial airflow and from the 0.5 % and 2 % alginate solutions using the vibration technology. The rate of bead production using the JetCutter was about 10 times higher than with the vibration technology and more than 10000 times higher than with the coaxial air-flow and electrostatic technology. In memory of our colleague Stefan Rosinski