Publication: Producción de etanol de segunda generación a partir de paja de trigo: hongos, enzimas fúngicas y aplicaciones
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2013-09-18
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Universidad Complutense de Madrid
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Abstract
La paja de trigo es una materia prima barata que no compite con los recursos alimentarios y una alternativa para producir combustibles de segunda generación (2G) como el bioetanol. Para el aprovechamiento de los azúcares de este residuo son imprescindibles tres etapas: pretratamiento, hidrólisis enzimática y fermentación de los azucares a etanol. En este contexto, el objetivo de este trabajo fue buscar alternativas para mejorar diferentes etapas del proceso de producción de etanol 2G a partir de paja de trigo. En primer lugar se muestrearon 21 hongos basidiomicetos en condiciones de fermentación en estado sólido (SSF), durante 3 semanas de incubación, para evaluar si el biopretratamiento puede ser una alternativa a los tratamientos físico-químicos. Sólo 6 hongos mejoraron la recuperación de azúcares fermentables respecto de la paja no biopretratada. La especie más eficiente fue Irpex lacteus, que rindió valores de recuperación de xilosa del 62% y de glucosa del 66% con una conversión a etanol del 90%. Para optimizar estos rendimientos, I. lacteus se sometió a diferentes condiciones de SSF. Sólo la adición de sales de Mn2+ mejoró la recuperación de glucosa (un 6%). Los estudios de secretómica revelaron por qué I. lacteus es tan eficiente durante el biopretratamiento, permitieron describir las enzimas implicadas en el proceso y identificar una nueva peroxidasa decoloradora de tintes (DyP). La enzima pura fue muy estable a pH ácido, altas temperaturas y elevadas concentraciones de H2O2, y además mejoró significativamente la digestibilidad de la celulosa de paja de trigo al suplementarla al cóctel de hidrólisis enzimática. Con otro fin biotecnológico, las enzimas del crudo de I. lacteus y la peroxidasa versátil de Pleurotus eryngii también fueron capaces de polimerizar moléculas como lignanos, péptidos, proteínas y arabinoxilanos feruloilados, generando productos con propiedades nuevas o diferentes.
Wheat straw is a cheap raw material which does not compete with food resources, constituting an alternative to produce second-generation (2G) biofuels such as bioethanol. To obtain the fermentable sugars from this residue, three steps are required: pretreatment, enzymatic hydrolysis, and sugars fermentation to ethanol. In this context, the aim of this work was to search alternatives to improve different process steps in 2G ethanol production from wheat straw. First of all, 21 basidiomycetes fungi were screened in solid state fermentation conditions (SSF), during 3 weeks of incubation, to evaluate if biopretreatment could be an alternative to physico-chemical pretreatments. Only 6 fungi increased the sugar yields compared to the non-biopretreated wheat straw. The most efficient species was Irpex lacteus, rendering a xylose yield of 62% and glucose yield of 66% with a 90% conversion to ethanol. With the objective of enhancing these yields, I. lacteus was subjected to different SSF conditions. Only Mn2+ addition increased glucose recoveries (6%). Secretomic studies revealed why I. lacteus was the most efficient fungus during the biopretreatment, allowed describing the enzymes implicated in that process, and identifying a new dye-decolorizing peroxidase (DyP). The purified enzyme was very stable to acid pH, high temperatures, and H2O2 concentrations. In addition, DyP increased significantly the cellulose digestibility of wheat straw when it was supplemented to the enzyme hydrolysis cocktail. Concerning other biotechnological applications, the crude´s enzymes of I. lacteus and the versatile peroxidase of Pleurotus eryngii were also capable of cross-linking diverse molecules such as lignans, peptides, proteins, and feruloylated arabinoxylans, generating products with new or different properties.
Wheat straw is a cheap raw material which does not compete with food resources, constituting an alternative to produce second-generation (2G) biofuels such as bioethanol. To obtain the fermentable sugars from this residue, three steps are required: pretreatment, enzymatic hydrolysis, and sugars fermentation to ethanol. In this context, the aim of this work was to search alternatives to improve different process steps in 2G ethanol production from wheat straw. First of all, 21 basidiomycetes fungi were screened in solid state fermentation conditions (SSF), during 3 weeks of incubation, to evaluate if biopretreatment could be an alternative to physico-chemical pretreatments. Only 6 fungi increased the sugar yields compared to the non-biopretreated wheat straw. The most efficient species was Irpex lacteus, rendering a xylose yield of 62% and glucose yield of 66% with a 90% conversion to ethanol. With the objective of enhancing these yields, I. lacteus was subjected to different SSF conditions. Only Mn2+ addition increased glucose recoveries (6%). Secretomic studies revealed why I. lacteus was the most efficient fungus during the biopretreatment, allowed describing the enzymes implicated in that process, and identifying a new dye-decolorizing peroxidase (DyP). The purified enzyme was very stable to acid pH, high temperatures, and H2O2 concentrations. In addition, DyP increased significantly the cellulose digestibility of wheat straw when it was supplemented to the enzyme hydrolysis cocktail. Concerning other biotechnological applications, the crude´s enzymes of I. lacteus and the versatile peroxidase of Pleurotus eryngii were also capable of cross-linking diverse molecules such as lignans, peptides, proteins, and feruloylated arabinoxylans, generating products with new or different properties.
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Biológicas, leída el 19/07/2013