Unraveling The Genetic Basis Of Xylose Consumption In Engineered Saccharomyces Cerevisiae Strains

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)The development of biocatalysts capable of fermenting xylose, a five-carbon sugar abundant in lignocellulosic biomass, is a key step to achieve a viable production of second-generation ethanol. In this work, a robust industrial strain of Saccharomyces cerevisiae was modified by the addition of essential genes for pentose metabolism. Subsequently, taken through cycles of adaptive evolution with selection for optimal xylose utilization, strains could efficiently convert xylose to ethanol with a yield of about 0.46 g ethanol/g xylose. Though evolved independently, two strains carried shared mutations: amplification of the xylose isomerase gene and inactivation of ISU1, a gene encoding a scaffold protein involved in the assembly of iron-sulfur clusters. In addition, one of evolved strains carried a mutation in SSK2, a member of MAPKKK signaling pathway. In validation experiments, mutating ISU1 or SSK2 improved the ability to metabolize xylose of yeast cells without adaptive evolution, suggesting that these genes are key players in a regulatory network for xylose fermentation. Furthermore, addition of iron ion to the growth media improved xylose fermentation even by non-evolved cells. Our results provide promising new targets for metabolic engineering of C5-yeasts and point to iron as a potential new additive for improvement of second-generation ethanol production.6BNDESFINEPBrazil's CAPESNational Institute of General Medical Sciences of the USA National Institutes of Health (NIGMS-NIH) [R35GM119788]Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Aa9 And Aa10: From Enigmatic To Essential Enzymes

The lignocellulosic biomass, comprised mainly of cellulose, hemicellulose, and lignin, is a strong competitor for petroleum to obtain fuels and other products because of its renewable nature, low cost, and non-competitiveness with food production when obtained from agricultural waste. Due to its recalcitrance, lignocellulosic material requires an arsenal of enzymes for its deconstruction and the consequent release of fermentable sugars. In this context, enzymes currently classified as auxiliary activity 9 (AA9/formerly GH61) and 10 (AA10/formerly CBM 33) or lytic polysaccharide monooxygenases (LPMO) have emerged as cellulase boosting enzymes. AA9 and AA10 are the new paradigm for deconstruction of lignocellulosic biomass by enhancing the activity and decreasing the loading of classical enzymes to the reaction and, consequently, reducing costs of the hydrolysis step in the second-generation ethanol production chain. In view of that disclosed above, the goal of this work is to review experimental data that supports the relevance of AA9 and AA10 for the biomass deconstruction field.100191

AA9 and AA10: from enigmatic to essential enzymes

The lignocellulosic biomass, comprised mainly of cellulose, hemicellulose, and lignin, is a strong competitor for petroleum to obtain fuels and other products because of its renewable nature, low cost, and non-competitiveness with food production when obtained from agricultural waste. Due to its recalcitrance, lignocellulosic material requires an arsenal of enzymes for its deconstruction and the consequent release of fermentable sugars. In this context, enzymes currently classified as auxiliary activity 9 (AA9/formerly GH61) and 10 (AA10/formerly CBM 33) or lytic polysaccharide monooxygenases (LPMO) have emerged as cellulase boosting enzymes. AA9 and AA10 are the new paradigm for deconstruction of lignocellulosic biomass by enhancing the activity and decreasing the loading of classical enzymes to the reaction and, consequently, reducing costs of the hydrolysis step in the second-generation ethanol production chain. In view of that disclosed above, the goal of this work is to review experimental data that supports the relevance of AA9 and AA10 for the biomass deconstruction field1001916sem informaçã