Microbial production of homogeneously layered cellulose pellicles in a membrane bioreactor.

Microbial cellulose (MC) is being investigated for various applications in the field of biomedical engineering. Gluconacetobacter xylinus is able to produce pure cellulose in the form of a hydrogel ("pellicle"). The pellicle consists of a defined tridimensional structure that is sensitive to mechanical stress during the process of formation. The bacteria, however, are obligate aerobic and need to be supplied with oxygen. These two objectives are often conflicting. A lab-scale membrane bioreactor prototype was developed which is able to efficiently produce a MC pellicle with a homogeneous layered structure. A hydrophilic microfiltration polyethersulfone membrane separates the bacteria from the cultivation medium. This setup allows the free convective exchange of the cultivation medium, while providing mechanical support for the continuous formation of the MC layer. Thickness of the MC layer was measured online by a laser triangulation sensor. One hundred and twenty five gram cellulose dry weight/m(2) membrane surface were produced within a process time of 330 h. Membrane bioreactors may be used to produce homogenous MC layers in a variety of shapes suitable for biomedical applications.

Purification and characterization of a 315 kDa keratinolytic subtilisin-like serine protease from Microsporum canis and evidence of its secretion in naturally infected cats.

A keratinolytic protease, secreted as the major component by a feline clinical isolate of Microsporum canis cultivated in a minimal medium containing cat keratin, was purified by affinity chromatography on bacitracin agarose and gel filtration. The apparent molecular mass of the enzyme was 31.5 kDa and the pI was 11.8. The enzyme was not glycosylated and its first 15 N-terminal amino acids showed numerous similarities with other fungal subtilisins. The optimum pH was around 9 while inactivation of the enzyme was reversible at pH 4, but not at pH 11. The enzyme was stable at 37 degrees C with an apparent optimum temperature around 55 degrees C. PMSF, soybean trypsin inhibitor (SBTI) and chymostatin strongly inhibited the proteinase. The highest affinity (Km of 0.37 mM) and physiological efficiency (k(cat)/Km) were obtained for the synthetic substrate N-Suc-Ala-Ala-Pro-Phe-p-nitroanilide. These results indicate that the keratinase belongs to the subtilisin-like serine protease family. Purified rabbit immunoglobulins G prepared against the keratinase and used in an immunohistochemical test allowed the detection of the keratinase produced by the fungus invading hair structures in naturally infected cats. The in vitro keratinolytic activity of the enzyme and its production in vivo suggest that it may contribute to pathogenicity.

Effect of Lithium on Thigmomorphogenesis in Bryonia dioica Ethylene Production and Sensitivity.

Rubbing internodes of Bryonia dioica plants reduced their ethylene production but increased their capacity to convert 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene. These results were explained by the previously shown rubbing-induced decrease of indoleacetic acid, which controls the level of ACC synthase, and by the increase of membrane-associated peroxidases which would participate in the conversion of ACC-ethylene. Pretreatment of the plants with Li had no significant effect on control plants but counteracted the rubbing-induced decrease of ethylene production and diminished the capacity of the internodes to convert ACC to ethylene. Exogenously applied ethylene induced an increase of peroxidase activity similar to that caused by rubbing. Inasmuch as both effects were reduced by Li, it was concluded that Li inhibition of thigmomorphogenetic processes was essentially due to a Li inhibition of the effect of ethylene formed in response to mechanical stimuli. The decreased ethylene production and ACC conversion capacity in the presence of Li were explained by a cellular redistribution of peroxidases.