BACTERIAL AND YEAST COMBINATIONS FOR REDUCING GREENHOUSE GAS PRODUCTION DURING FERMENTATION OF BIOMASS COMPRISING HEXOSES

1 . A combination for making ethanol from a biomass comprising hexoses, the combination comprising a yeast host cell and a bacterial host cell, wherein:

the bacterial host cell has:

a first metabolic pathway comprising one or more first polypeptides for converting acetate into ethanol;

a second metabolic pathway comprising one or more second polypeptides for the conversion of glycerol into dihydroxyacetone-phosphate; and

a third metabolic pathway comprising one or more third heterologous polypeptides for converting pyruvate into ethanol; and

the yeast host cell has:

a fourth metabolic pathway comprising one or more fourth polypeptides for producing glycerol; and

a fifth metabolic pathway comprising one or more fifth polypeptides for generating acetate.

2 . The combination of claim 1 , wherein the hexoses comprise glucose and/or the biomass comprises or is derived from corn.

3 . The combination of claim 1 , wherein the one or more first polypeptides comprises:

one or more native or heterologous enzymes for converting acetate into acetyl-CoA; and/or

one or more native or heterologous enzymes for converting acetyl-CoA into acetaldehyde, and optionally acetaldehyde into ethanol.

4 . The combination of claim 3 , wherein:

the one or more native or heterologous enzymes for converting acetate into acetyl-CoA comprise:

a polypeptide having an acetate kinase (ACK) activity;

a polypeptide having phosphotransacetylase (PTA) activity; and/or

a polypeptide having acetyl coA-synthetase (ACS) activity; and/or

the one or more native or heterologous enzymes for converting acetyl-CoA into acetaldehyde, and optionally acetaldehyde into ethanol comprise:

a polypeptide having acetaldehyde-dehydrogenase (AADH) activity;

a polypeptide having an alcohol dehydrogenase (ADH) activity); and/or

a polypeptide having a bifunctional acetaldehyde/alcohol dehydrogase (ADHE) activity.

5 . The combination of claim 1 , wherein the second metabolic pathway is for the dehydrogenation of glycerol.

6 . The combination of claim 5 , wherein the one or more second polypeptides comprise:

a native or heterologous polypeptide having glycerol dehydrogenase (GLDA) activity or a combination of the native and the heterologous polypeptides having GLDA activity,

a native or heterologous polypeptide having an ATP-dependent dihydroxyacetone kinase (DAK) activity, and/or

a native or heterologous polypeptide having a PEP-dependent dihydroxyacetone kinase (DHAKLM) activity or a combination of a native and a heterologous polypeptides having DHAKLM activity.

7 . The combination of claim 1 , wherein the one of or more third heterologous polypeptides comprise:

a native or heterologous polypeptide having pyruvate decarboxylase (PDC) activity, and/or

a native or heterologous polypeptide having alcohol dehydrogenase (ADH) activity.

8 . The combination of claim 1 , wherein the bacterial host cell is a lactic acid bacterium.

9 . The combination of claim 8 , wherein the bacterial host cell is from Lactiplantibacillus sp. or from Lacticaseibacillus sp.

10 . The combination of claim 8 , wherein the bacterial host cell has a decreased lactate dehydrogenase activity and optionally at least one inactivated native gene coding for a lactate dehydrogenase.

11 . The combination of claim 1 , wherein the bacterial host cell includes at least one genetic modification:

for reducing carbon catabolite repression, when compared to a control bacterial host cell lacking the at least one genetic modification; or

for decreasing the expression or inactivating at least one gene encoding a polypeptide involved in a glycolytic flux

12 . The combination of claim 11 , wherein:

the at least one genetic modification for reducing carbon catabolite repression comprises a genetic modification decreasing the expression or inactivating a gene encoding a phosphoenolpyruvate-dependent phosphotransferase (PTS) transporter; and/or

the at least one gene encoding the polypeptide involved in a glycolytic flux comprises a gene encoding a glucose permease, a maltose/maltodextrin transporter, a kinase and/or a transcription factor, optionally wherein the transcription factor is REX.

13 . The combination of claim 1 , wherein the one or more fourth polypeptides comprise:

a native or heterologous polypeptide having glycerol-3-phosphate dehydrogenase activity, and/or

a native or heterologous polypeptide having glycerol-3-phosphate phosphatase activity.

14 . The combination of claim 1 , the one or more fifth polypeptides for generating acetate comprise:

one or more native or heterologous polypeptides having phosphoketolase activity, wherein the phosphoketolase has single specificity or dual specificity and optionally exhibits a phosphatase activity.

15 . The combination of claim 1 , wherein the yeast host cell is from Saccharomyces sp.

16 . A bacterial host cell for making ethanol from a biomass comprising hexoses, the bacterial host cell comprising:

a first metabolic pathway comprising one or more first polypeptides for converting acetate into ethanol;

a second metabolic pathway comprising one or more second polypeptides for the converting glycerol into dihydroxyacetone phosphate; and

a third metabolic pathway comprising one or more third heterologous polypeptides for converting pyruvate into ethanol.

17 . A composition comprising the combination claim 1 and a biomass comprising hexoses.

18 . A process for converting a biomass comprising hexoses into ethanol, the process comprising contacting the biomass with the combination of claim 1 under a condition to allow the conversion of at least a part of the biomass into ethanol.

19 . A process for reducing the emission of CO 2 during the conversion of a biomass into ethanol, the process comprising contacting the biomass with the combination of claim 1 under a condition to allow the conversion of at least a part of the biomass into ethanol, wherein the reduction in the emission of CO 2 is observed when comparing a process performed in the absence of the bacterial host cell.

20 . A process for improving the fermentation yield during the conversion of a biomass comprising hexoses into ethanol, the process comprising contacting the biomass with the combination of claim 1 under a condition to allow the conversion of at least a part of the biomass into ethanol, wherein the improvement in the fermentation yield is observed compared to a control process performed in the absence of the bacterial host cell.