RESUMO
Xylanases assume special importance in the paper and pulp industry as they replace toxic chemicals such as chlorine and chlorine dioxide for developing eco-friendly processes. This study evaluated xylanases produced by two fungi, the mesophilic fungus Trichoderma harzianum and a thermophilic fungus Chaetomium thermophilum. Among the polymeric substrates studied for xylanase production by both the fungi, birch wood xylan was found to be the best inducer of xylanases. Xylanases induction was subject to glucose repression. Partially purified xylanases preparation from T. harzianum and C. thermophilum exhibited optimal activities at pH 5 and 6 and at 60ºC and 70ºC, respectively. The apparent Km and Vmax values for the partially purified xylanase from T. harzianum using oat spelt xylan as a substrate were 4.8 mg mL-1 and 0.526 µmol min-1 mg-1, respectively. Whereas values of the partially purified xylanase from C. thermophilum were 2.96 mg mL-1 and 0.25 µmol min-1 mg-1, respectively. These findings in this study have great implications for the future applications of xylanases.
Assuntos
Chaetomium/enzimologia , Trichoderma/enzimologia , Concentração de Íons de Hidrogênio , Cinética , TemperaturaRESUMO
Different Trichoderma species were examined for their abilities to persist within the maize (Zea mays) stem at different points above and below inoculation points. Different Trichoderma species were isolated from different parts of the maize (Z. mays) plant and its rhizosphere. They were later sent to International Mycological Institute, England for identification. Maize seeds (DMR-LSRW) were planted in pots in the screenhouse. Four weeks after planting, each of the Trichoderma species was inoculated into the stems of the potted plants at the 2nd internodes using the toothpick method. Toothpicks dressed with sterile distilled water served as control. Cut sections of the inoculated stems were examined for presence or absence of the inoculated Trichoderma species at different points far from the inoculated point in the upper and lower internodes after 2, 3, 4, 5 and 6 weeks of inoculation. Ten Trichoderma species were identified; these include five strains of T. pseudokoningii, three strains of T. harzianum, T. hamatum and T. longibrachiatum. All the Trichoderma species were able to move within the stem tissues into the upper and lower internodes. All of them were re-isolated at distant points from inoculation point in the upper and lower internodes even after 6 weeks of inoculation. T. pseudokoningii strain 2 and T. harzianum strains 1 to 3 had the best endophytic movement into the upper and lower internodes. T. hamatum and T. longibrachiatum had the weakest movement into the upper and lower internodes. All the Trichoderma species could thus be said to possess the abilities to persist (endophytic capability) within the maize (Z. mays) stem. T. pseudokoningii and T. harzianum could also be said to be among the best species in the genus Trichoderma with good prospect of biocontrol potential.
RESUMO
La podredumbre blanda (Rhyzopus stolonifer), la podredumbre negra (Mucor spp., Aspergillus niger y Pythium spp.) son las enfermedades postcosecha más comunes de la fresa (Fragaria spp.) y generan grandes pérdidas de estas. Durante muchos años se han utilizado fungicidas sintéticos para controlar a estos patógenos, pero se ha demostrado que se hacen resistentes a dichos productos, además de representar un riesgo potencial al ambiente y la salud humana. Todo esto ha conllevado a la búsqueda de alternativas naturales como el empleo de extractos vegetales y antagonistas microbianos, siendo Trichoderma harzianum el antagonista mas utilizado como control biológico. El objetivo de este estudio fue determinar el efecto antagónico de T. harzianum sobre algunos hongos patógenos postcosecha en fresa y conocer su mecanismo de acción. Las muestras de fresa fueron transportadas al laboratorio en los mismos empaques de venta, y posteriormente las fresas fueron colocadas en cámaras de germinación controlando la humedad para el desarrollo rápido de hongos presentes en la fruta. Se identificaron los hongos Rhyzopus stolonifer, Mucor spp., Penicillium digitatum, Rhizoctonia solani, Aspergillus niger y Pythium spp., sobre los cuales se realizó la prueba de antagonismo usando al hongo T. harzianum. La velocidad de crecimiento del biocontrolador fue mayor que el crecimiento de los hongos postcosecha (p<0,01) y a las 96 horas de incubación la caja de Petri estaba completamente cubierta y en la zona de encuentro entre éstos se observó que el mecanismo de acción del biocontrolador fue de tipo micoparasítico. T. harzianum resultó ser un excelente controlador in vitro de hongos postcosecha de frutos de fresa.
Soft rotting (Rhyzopus stolonifer) and black rotting (Mucor spp., Aspergillus niger and Pythium spp.) are the most common post harvesting strawberry (Fragaria spp.) diseases, generating great losses. During many years synthetic fungicides have been used to control these pathogens, but their development of resistance to these products has been demonstrated, following to the fact that they represent a potential environmental and human health risk. This has lead to the search of natural alternatives such as the use of vegetal extracts and microbial antagonists, being Trichoderma harzianum the antagonist most widely used as biological control. The purpose of this study was to determine the antagonist effect of T. harzianum over some post strawberry harvesting pathogens and determine their mechanism of action. The strawberry samples were transported to the laboratory in the same packages in which they were sold, and then were placed in germination chambers, controlling humidity to obtain a rapid development of the fungi present in the fruit. We identified the following fungi: Rhyzopus stolonifer, Mucor spp., Penicillium digitatum, Rhizoctonia solani, Aspergillus niger and Phytium spp., which were tested for antagonism, using the T. harzianum. The growth speed of the biocontroller was greater than that of the post harvest fungi (p<0,01) and at 96 hours of incubation the Petri dish was completely covered, and the encounter area between them showed that the action mechanism of the biocontroller was of the mycoparasitic type. T. harzianum turned out to be an excellent in vitro controller of post strawberry harvest fungi.