Immobilisation and kinetics of Penicillium notatum dextranase on controlled porous glass

Two highly purified enzymic fractions of dextranase (1,6-- -glucan 6-glucanohydrolase, EC 3.2.1.11) from Penicillium notatum have been immobilised on silanised porous glass modified by glutaraldehyde, carbodiimide and bis-oxirane binding. The marked shifts in the pH and temperature optima as well as the changes in the kinetics (K_m, V_max, E_a) of the solid-phase dextranases were observed and discussed. The immobilisation of enzymes on alkylamine glass through the process of glutaraldehyde coupling proved to be the best of the methods studied. The dextranase preparations obtained in this way showed a catalytic activity at wider pH and temperature ranges than those of the free enzymes. They were also characterized by a relatively high affinity to the substrate and good storage stability. The usefulness of the bound dextranase in batch and column hydrolysis of dextran was also established.     

Purification and characterization of extracellular dextranase from a novel producer, Hypocrea lixii F1002, and its use in oligodextran production

Fungi were isolated from natural soil samples and screened for extracellular dextranase synthesis. The strain F1002 was identified as Hypocrea lixii using a standard internal transcribed spacer ribosomal DNA analysis and was selected for extracellular dextranase synthesis. The enzyme was purified via ammonium sulfate precipitation and Sepharose 6B chromatography, which resulted in an 8.3-fold increase in the specific activity and a 10.73% recovery. This enzyme is a monomeric protein with a molecular mass of 62 kDa, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified enzyme, which was identified as an endodextranase, had an optimum pH of 5.0 and an optimum temperature of 25 °C. The dextranase activity was enhanced by Mg²⁺, Al³⁺, and especially Zn²⁺ at a low concentration, which improved its activity to 124.22%. The enzyme has a very high hydrolytic affinity toward high-molecular weight dextrans. Setting the concentrations of the H. lixii F1002 dextranase (2.31 U/mL) and dextrans (6%), as well as the reaction time (45 min), allowed the dextranase to hydrolyze dextrans of controlled molecular weights (20–70 kDa). Three types of oligodextrans with different molecular weights (namely, 69,376, 38,251, and 21,364 Da) were obtained, with a total yield of 80.32%.     

Porosity and tortuosity relations as revealed by a mathematical model of biofilm structure

A biofilm is assumed to be submerged in a fluid with given viscosity and low Reynolds number. The interaction between fluid and bacteria is modeled through streamlines. We use finite-difference and boundary element numerical schemes to predict streamlines within the biofilm. The results show that this approach can provide information about prior distribution and geometry of the biofilm structure. Theoretical values of porosity and tortuosity are computed and compared with published data.     

Detachment forces and their influence on the structure and metabolic behaviour of biofilms

The biofilm reactor has been frequently applied in wastewater treatment. The formation, structure and metabolic activity of the biofilms are closely associated with the detachment forces in the reactors. This paper reviews the essential role of detachment forces in the biofilm process. A more compact, stable and denser biofilm can be formed at a relatively higher detachment force. The detachment force has significant influence on the structure, mass transfer, production of exopolysaccharides, metabolic and genetic properties of the biofilm. In an engineering sense, the detachment forces can be manipulated, as a control parameter, to produce a more stable and compact biofilm for use in wastewater treatment. The molecular and genetic mechanisms responsible for the detachment force-associated phenomena are not yet fully understood.     

The influence of EDTA on the composition of alginate synthesized by Azotobacter vinelandii

1. During an investigation of the physiology of Azotobacter vinelandii with particular reference to polysaccharide formation, a suitable medium which was precipitate-free was developed by adding EDTA at a concentration of 50 mg/l to a basal medium containing one of eight different carbohydrates as sole carbon source.
2. Acetylated alginate was always produced by the organism when cultured under defined conditions, regardless of the carbohydrate source incorporated in the basal medium.
3. When EDTA was added to the medium, the bacteria produced acetylated polyuronides with a preponderance of mannuronic acid residues.
4. A comparison of the infrared spectra of the alginate produced by Azotobacter vinelandii and the affect of EDTA upon the mannuronic acid/guluronic acid ratios of the alginate are reported.

     

Effects of Magnolol and Honokiol on the activities of streptococcal glucosyltransferases both in solution and adsorbed on an experimental pellicle

AIMS: To investigate the inhibitory effects of Magnolol and Honokiol on the activity of streptococcal glucosyltransferases (Gtfs). METHODS AND RESULTS: The effect of Magnolol and Honokiol that inhibits the activities of streptococcal GtfB, GtfC, GtfD and GtfS was explored with standard assays. The results showed that both samples can efficiently inhibit the activity of all Gtfs in solution (66.4-96.3%) and adsorbed on the surface of saliva-coated hydroxyapatite (sHA) beads (65.5-92.7%) at concentrations between 1.25 and 5.0 mg ml(-1). Furthermore, Magnolol had a stronger inhibition of four kinds of Gtfs than Honokiol both in solution and adsorbed on the surface of sHA beads at concentrations between 0.04 and 0.63 mg ml(-1) (P < 0.05). CONCLUSIONS: Magnolol had significant effects on the activities of streptococcal Gtfs. SIGNIFICANCE AND IMPACT OF THE STUDY: Magnolol as a natural herb can be developed into a new oral hygiene product to prevent plaque formation.     

The structure and function of glycoproteins synthesized during slime-polysaccharide production by membranes of the root-cap cells of maize (Zea mays).

The synthesis of the maize root slime polysaccharides was investigated by using [1-3H]-fucose as a marker for slime production. Three fractions were separated by centrifugation in a CsCl density gradient. Two of these were glycoproteins and occurred within the membranes of the cells of the root tip; the third was the slime polysaccharides. Radioactive pulse-chase experiments showed that the glycoproteins were precursors of the slime polysaccharides, and the carbohydrate portion of the glycoproteins had a similar composition to that of the free slime. The linkage between the protein and the carbohydrate of one of the glycoproteins was shown to be a xylose-threonine bond. It is postulated that the slime polysaccharides are synthesized and transported on proteins within the membrane system of the root tip.     

Volume changes during enzyme reactions. The influence of pressure on the action of invertase, dextranase and dextransucrase.

The pressure dependence of the maximum velocities and the Michaelis constants for the enzymes invertase and dextranase was measured up to 1400 bar. The corresponding activation volumes deltaV not equal to c and deltaV not equal to Km proved to be independent of pressure. Together with data from other sources the meaning of deltaV not equal to c and deltaV not equal to Km is established and the volume profiles of the reactions are constructed. These profiles are similar in contour to the volume profile of the dextran formation catalyzed by the enzyme dextransucrase, but the amount of the volume changes is very much larger for dextransucrase. The evaluation of salt effects shows, that for all three enzymes solvent interactions are not important in explaining the results. The reaction mechanisms seem to be governed by conformation changes of the enzymes. The larger effects in dextransucrase are explained by the produced dextran chain remaining tightly bound to the enzyme and being transported relative to the enzymes position in each reaction cycle.     

The influence of carbon sources and morphology on nystatin production by Streptomyces noursei

Carbon source nutrition and morphology were examined during cell growth and production of nystatin by Streptomyces noursei ATCC 11455. This strain was able to utilise glucose, fructose, glycerol and soluble starch for cell growth, but failed to grow on media supplemented with galactose, xylose, maltose, sucrose, lactose and raffinose. Utilisation of glucose had a negative influence on production of nystatin independent of the specific growth rate when phosphate and ammonium was in excess. Consumption of carbon sources was related to the specific growth rate. S. noursei ATCC 11455 formed mainly mycelial clumps during cultivation, while pellet growth dominated the culture of the morphologically altered high producing mutant S. noursei NG7.19. When the pellet size increased above a critical size, cell growth and nystatin production terminated. Fluorescent staining of hyphae revealed that this coincided with loss of activity inside the core of the pellets, probably due to diffusion limitation of oxygen or other nutrients.