Yeast cells are transformed with an exogenous xylose isomerase gene. Additional genetic modifications enhance the ability of the transformed cells to ferment xylose to ethanol or other desired fermentation products. Those modifications include deletion of non-specific or specific aldose reductase gene(s), deletion of xylitol dehydrogenase gene(s) and/or overexpression of xylulokinase.

Yeast cells are transformed with an exogenous xylose isomerase gene. Additional genetic modifications enhance the ability of the transformed cells to ferment xylose to ethanol or other desired fermentation products. Those modifications include deletion of non-specific or specific aldose reductase gene(s), deletion of xylitol dehydrogenase gene(s) and/or overexpression of xylulokinase.

Provided herein are methods of making microorganisms modified for increased xylose consumption as compared to unmodified microorganisms. The methods include providing xylose-consuming microorganisms comprising two or more copies of a nucleic acid sequence encoding xylose isomerase and two or more copies of a nucleic acid sequence encoding a xylose kinase, culturing the microorganisms in medium containing xylose and harvesting a portion of the microorganisms. These steps are repeated multiple times. The microorganisms are then isolated. The isolated microorganisms have increased xylose consumption rates compared to control xylose-consuming microorganisms. Also provided are a population of microorganisms made by the provided methods. Methods of culturing the population of microorganisms and methods of reducing xylitol production in cultures comprising the population of microorganisms are provided.

The invention relates to a method for preparing a yeast which is capable of simultaneously fermenting a pentose and a hexose sugar, the method comprising providing a yeast which comprises: one or more heterologous genes encoding an enzyme of a pentose metabolic pathway, a disruption of a gene encoding a ribulose-phosphate 3-epimerase and a disruption of a gene encoding a glucose-6-phosphate isomerase, and one or more overexpressed endogenous genes encoding an enzyme of the pentose phosphate pathway; and subjecting the yeast to evolutionary engineering on a medium comprising a hexose sugar and at least one pentose sugar, selecting for a yeast with improved growth rate when grown on a media comprising a hexose and at least one pentose sugar, so as to obtain an evolved yeast.

The invention relates to a method for preparing a yeast which is capable of simultaneously fermenting a pentose and a hexose sugar, the method comprising providing a yeast which comprises: one or more heterologous genes encoding an enzyme of a pentose metabolic pathway, a disruption of a gene encoding a ribulose-phosphate 3-epimerase and a disruption of a gene encoding a glucose-6-phosphate isomerase, and one or more overexpressed endogenous genes encoding an enzyme of the pentose phosphate pathway; and subjecting the yeast to evolutionary engineering on a medium comprising a hexose sugar and at least one pentose sugar, selecting for a yeast with improved growth rate when grown on a media comprising a hexose and at least one pentose sugar, so as to obtain an evolved yeast.

Disclosed herein are methods of producing hexoses from saccharides by improved enzymatic processes. The improved processes utilize enzymes with higher activities than those previously reported to convert starch or a starch derivative, cellulose or a cellulose derivative, or sucrose to a glucose 6-phosphate (G6P) intermediate.

Disclosed herein are methods of producing hexoses from saccharides by enzymatic processes. The methods utilize fructose 6-phosphate and at least one enzymatic step to convert it to a hexose.

Disclosed herein are methods of producing hexoses from saccharides by enzymatic processes. The methods utilize fructose 6-phosphate and at least one enzymatic step to convert it to a hexose.

In various aspects and embodiments, the invention provides microbial cells and methods for producing advanced glycosylation products from lower glycosylated intermediates. The microbial cell expresses one or more UDP-dependent glycosyl transferase enzymes in the cytoplasm, for glycosylation of the intermediates. When incubating the microbial strain with a plant extract or fraction thereof comprising the intermediates, these glycosylated intermediates are available for further glycosylation by the cell, and the advanced glycosylation products can be recovered from the media and/or microbial cells.

This disclosure provides epimerase enzymes useful for commercial scale production of allulose from fructose. The disclosed enzymes (“epimerase variants”) are variants of Burkholderia multivorans CGD1 xylose isomerase engineered to have improved catalytic activity of about 1.5- to 2-fold compared with the parent enzyme.