Growth rate inhibition of phytopathogenic fungi by characterized chitosans

The inhibitory effects of fifteen chitosans with different degrees of polymerization (DP) and different degrees of acetylation (F A) on the growth rates (GR) of four phytopathogenic fungi (Alternaria alternata, Botrytis cinerea, Penicillium expansum, and Rhizopus stolonifer) were examined using a 96-well microtiter plate and a microplate reader. The minimum inhibitory concentrations (MICs) of the chitosans ranged from 100 µg × mL-1 to 1,000 µg × mL-1 depending on the fungus tested and the DP and F A of the chitosan. The antifungal activity of the chitosans increased with decreasing F A. Chitosans with low F A and high DP showed the highest inhibitory activity against all four fungi. P. expansum and B. cinerea were relatively less susceptible while A. alternata and R. stolonifer were relatively more sensitive to the chitosan polymers. Scanning electron microscopy of fungi grown on culture media amended with chitosan revealed morphological changes.

Production of Alkali-Tolerant Xylanases from Bacillus pumilus and application in pre-bleaching of kraft pulps

This work investigated the production of alkali-tolerant xylanases produced by Bacillus pumilus. Xylanases active at alkaline conditions and high temperatures have great potential for industrial application, such as the bleaching process in pulp and paper industry, without need for cooling or changes in pH and whith the advantage in lowering the release of polluting organic chlorine compouds. Optimal condition of cellulase-free xylanase in submerged fermentation were developed. The highest xylanase production in culture flasks, 129 U/mL at pH 9 and 55 C, was obtained in 20 hours of fermentation, with 3(per cent) xylan, 0,6(per cent) peptone, 0,15(per cent) ammonium sulphate at pH 9,5, achieving a productivity of 6.5 UmL -1h-1. The productivity raised to 17.3 UmL -1h-1 when the xylanase was produced in 2.0 L bioreator. Xylanase form crude fermented broth was applied for pre bleaching of harwood kraft pulp. A decrease of 2,5 units in kappa number 26(per cent) delignification) was observed, indicating the potential for the alkaline xylanase from B. pumilus.