Blanca I. Escudero-Abarca

Bacillus thuringiensis var israelensis was used to produce chitinase on shrimp wastes by fermentation at 30°C and 250 rpm for 120 h. The enzyme was concentrated by ultrafiltration and was adjusted to pH 5.8. Antifungal chitinase activity on phytopathogenic fungi was investigated in growing cultures and on soybean seeds infested with Sclerotium rolfsii . Fungal inhibition was found to be 100% for S. rolfsii ; 55% to 82% for A. terreus , A. flavus, Nigrospora sp, Rhizopus sp, A. niger , Fusarium sp, A. candidus, Absidia sp, and Helminthosporium sp; 45% for Curvularia sp; and 10% for A. fumigatus (P < 0.05). When soybean seeds were infected with S. rolfsii , germination was reduced from 93% to 25%; the addition of chitinase (0.8 U/mg protein) increased germination to 90%. B. thuringiensis chitinase may contribute to the biocontrol of S. rolfsii and other phytopathogenic fungi in soybean seeds in Integrated Pest Management programs.

The effect of chitosan on Saccharomyces cerevisiae (the yeast that carries out alcohol fermentation), Brettanomyces bruxellensis and Brettanomyces intermedius (contaminants of alcohol fermentations), was investigated. The effect of chitosan was tested on each yeast, as well as on mixed cultivations of S. cerevisiae + B. bruxellensis and S. cerevisiae + B. intermedius. Chitosan enhanced the lag period of both strains of Brettanomyces (80 h for B. bruxellensis and 170 h for B. intermedius with 6 and 2 g/l chitosan, respectively). The growth rate of S. cerevisiae was inversely proportional to the chitosan concentration; the former was 50% when 6 g/l polysaccharide was used. Moreover, in mixed cultivations of S. cerevisiae and Brettanomyces strains, it was found that both B. bruxellensis and B. intermedius failed to grow while growth of S. cerevisiae was not affected (using 3 and 6 g/l chitosan, respectively). An interesting collateral result was that the presence of chitosan accelerated the consumption of glucose in the mixed cultivations (60 h instead of 120 h).