XYLANASES AND PECTINASES OF Aspergillus flavus CECT-2687 ON DIFFERENT CARBON SOURCES AND INITIAL pH VALUES

Abstract

Aspergillus flavus is a saprophytic opportunistic plant pathogen that infects crops and stored grains, in a process assisted by the action of enzymes, such as xylanases and pectinases. The enzymatic potential of A. flavus has not been addressed in detail, even when this knowledge could be useful for the understanding of the colonization dynamics during the grains spoilage by fungi, in order to find of strategies to control it. The effect of carbon source and pH on enzyme production was evaluated by growing A. flavus CECT-2687 in liquid cultures on different monosaccharides, polysaccharides or agricultural residues, at several initial pH values. The results showed a significant effect of pH, carbon source and the interaction of both factors. Xylanases were produced on monosaccharides, although the highest xylanolytic activities were obtained on agroindustrial xylan-rich residues. Exopectinases titers were similar on polysaccharides and agricultural residues, and were not observed on monosaccharides. Pectin lyases were produced on pectin and agricultural residues; and a pectin lyase of 27 kDa was identified in crude extracts of lemon peel cultures at initial pH of 8. The highest enzymatic productions were obtained on cultures with initial pH of 8. Keywords: xylanases, exopectinases, pectin lyases, agroindustrial residues, Aspergillus flavus CECT-2687. ResumenAspergillus flavus es saprofito y patógeno oportunista de cultivos y granos almacenados, en un proceso asistido por la acción de enzimas como xilanasas y pectinasas. El potencial enzimático de A. flavus no se ha abordado en detalle, incluso cuando este conocimiento podría ser útil para comprender la dinámica de colonización de granos por hongos y encontrar estrategias para su control. El efecto de la fuente de carbono y el pH sobre la producción de enzimas se evaluó cultivando A. flavus CECT-2687 en cultivos líquidos en diferentes monosacáridos, polisacáridos o residuos agrícolas, a diferentes valores de pH. Se encontró un efecto significativo del pH, la fuente de carbono y su interacción. Las xilanasas se produjeron en monosacáridos, las actividades más elevadas se obtuvieron en residuos agroindustriales ricos en xilano. Los títulos de exopectinasas fueron similares en polisacáridos y residuos agrícolas y no se observaron en monosacáridos. Las pectin liasas se produjeron en pectina y residuos agrícolas; y se identificó una pectina liasa de 27 kDa en extractos crudos de cultivos de cáscara de limón a pH inicial de 8. La mayor producción de todas las enzimas se observó en los cultivos con pH inicial de 8.