Trichoderma koningii and Trichoderma harzianum as destructive mycoparasites of Sclerotinia slerotiorum.

Three T. koningii (Tk 3, 5 and 12) and one T. harzianum (Th 9) strain isolated from S. sclerotiorum sclerotia were found to reduce the growth of the patogens by over 60% relative to that of the control. These strains also hyperparasited the sclerotia. All were also highly competitive when assessed in the saprophytic competitiveness test. Extra cellular enzyme production was not particularly correlated with antagonistic activity, Tk 12 and Th 9 produced some Beta-glucosidase and no endoglucanase. In contrast, Tk3, 5 and 12 produced large amounts of antibiotics, causing between 30% and 80% inhibition of growth of the pathogen. The interactions between T. harzianum strain and S. sclerotiorum appeared to be mycoparasitism, and results from the sclerotial survival tests showed they were also capable of destroying sclerotia

Isolation of mutants of Trichoderma harzianum with enhanced b-glucosidase production with ability to inhibit and the plant pathogen Sclerotinia sclerotiorum.

Antagonism of Trichoderma spp. against other microrganisms in general operates by exolysis, breaking down the walls of fungal pathogens. Trichoderma species seem to be the best source of extracellular cellulase that can solubilize highly ordered cellulose. Cell walls of sclerotia of slerotiorum usually contain chitin and b-glucans. Such sclerotia may be vulnerable to attack by many microrganisms. The objective of this research was the isolation of improved strains for b-glucosidase production. The new biotypes obtained from a wild strain of T. harzianum were isolated via UV light in solid medium containing wheat-bran. Two mutants produced significant amounts of extra cellular cellulase activity with b-glucosidase activity. The percentage of reduction of colony of S. sclerotiorum by antifungal activity was observed in vitro. The mutant 15+ presented 73% of inhibition of micelial growth. Hyphae morphology of the mutant strain, studied by SEM, shows that the hyphae tips are extremely branched. The wild-type did not produced any antibiotic activity

Osmotic regulation of porin expression: a role for DNA supercoiling

The OmpC and OmpF porins are major outer membrane proteins of Escherichia coli and Salmonella typhimurium. Their expression is affected by many environmental factors and by mutations in a variety of independent genes. The pair of regulatory proteins, OmpR and EnvZ, are required for normal porin expression. Despite intensive investigation, the mechanisms by which porin expression is regulated remain unclear. Mutations which alter supercoiling, as well as inhibitors of DNA gyrase, show that porin expression is extremely and specifically sensitive to the level of DNA supercoiling. Our data lead us to suggest that environmentally induced changes in DNA supercoiling may play a role in determining the level of porin expression. These findings have implications for current models of porin regulation