PRODUCTION OF ISOPRENE UNDER NEUTRAL pH CONDITIONS

3-4. (canceled)

(canceled)

(canceled)

34-35. (canceled)

A system for producing isoprene comprising (i) a bioreactor within which saccharification and fermentation are performed at pH 6.5 to 8.0;

• (ii) a host cell comprising a heterologous nucleic acid encoding an isoprene synthase polypeptide;
• (iii) a glucoamylase that possesses at least 50% activity at pH 6.0 or above relative to its maximum activity, wherein the glucoamylase is Trichoderma reesei glucoamylase (TrGA) comprising SEQ ID NO:
• 6, or a variant thereof, and wherein the variant has at least 99% sequence identity to the parent glucoamylase, wherein the host cell is selected from the group consisting of bacterial cells and fungal cells.

A method for producing isoprene comprising culturing a host cell, which comprises a heterologous nucleic acid encoding an isoprene synthase polypeptide, and saccharifying and fermenting a starch substrate under simultaneous saccharification and fermentation (SSF) conditions in the presence of a glucoamylase and at least one other enzyme, wherein the saccharification and fermentation are performed at pH 6.5 to 8.0, wherein the glucoamylase possesses at least 50% activity at pH 6.0 or above relative to its maximum activity, wherein the glucoamylase is Trichoderma reesei glucoamylase (TrGA) comprising SEQ ID NO:

• 6, or a variant thereof, and wherein the variant has at least 99% sequence identity to a parent glucoamylase, and wherein the other enzyme is selected from the group consisting of proteases, pullulanases, isoamylases, cellulases, hemicellulases, xylanases, cyclodextrin glycotransferases, lipases, phytases, laccases, oxidases, esterases, cutinases, xylanases, and alpha-glucosidases, wherein the host cell is selected from the group consisting of bacterial cells and fungal cells.

A method for producing isoprene comprising culturing a host cell, which comprises a heterologous nucleic acid encoding an isoprene synthase polypeptide, and saccharifying and fermenting a starch substrate under simultaneous saccharification and fermentation (SSF) conditions in the presence of a glucoamylase and at least one other non-starch polysaccharide hydrolyzing enzyme, wherein the saccharification and fermentation are performed at pH 6.5 to 8.0, wherein the glucoamylase possesses at least 50% activity at pH 6.0 or above relative to its maximum activity, wherein the glucoamylase is Trichoderma reesei glucoamylase (TrGA) comprising SEQ ID NO:

• 6, or a variant thereof, and wherein the variant has at least 99% sequence identity to a parent glucoamylase, and wherein the non-starch polysaccharide hydrolyzing enzyme is selected from the group consisting of cellulases, hemicellulases and pectinases, wherein the host cell is selected from the group consisting of bacterial cells and fungal cells.