Limiting yeast-produced trehalose in fermentation

A process for converting a substrate into a fermentation product, the process comprising contacting biomass comprising the substrate with a recombinant yeast host cell under conditions to allow conversion of at least a part of the substrate into the fermentation product, wherein the recombinant yeast host cell comprises:

• (i) a first genetic modification for reducing production of one or more native enzymes that function to produce glycerol or regulating glycerol synthesis and/or allowing production of an heterologous glucoamylase, wherein
• the first genetic modification for reducing the production of the one or more native enzymes that function to produce glycerol and the one or more native enzymes that function to produce glycerol is glycerol-3-phosphate dehydrogenase 1 (GPD1), a polypeptide encoded by a gpd1 ortholog, glycerol-3-phosphate dehydrogenase 2 (GPD2) polypeptide and/or a polypeptide encoded by a gpd2 ortholog;
• the first genetic modification for regulating glycerol synthesis is for reducing production of FDP1 suppressor (FPS1) polypeptide or a polypeptide encoded by a fps1 ortholog and/or is for increasing production of sugar transporter-like (STL1) polypeptide and/or a polypeptide encoded by a stl1 ortholog, and
• (ii) a second genetic modification for reducing production of one or more native enzymes that function to produce trehalose or regulating trehalose synthesis and/or allowing expression of an heterologous trehalase, wherein
• the second genetic modification for reducing the production of one or more native enzymes that function to produce trehalose and the one or more native enzymes that function to produce trehalose is trehalose-6-phosphate synthase 1 (TPS1), a polypeptide encoded by a tps1 ortholog, trehalose-6-phosphate synthase 2 (TPS2) polypeptide and/or a polypeptide encoded by a tps2 ortholog;
• the second genetic modification for regulating trehalose synthesis is for reducing production of one or more native enzymes regulating trehalose synthesis and the one or more native enzymes regulating trehalose synthesis is trehalose phosphate synthase (TPS3), a polypeptide encoded by a tps3 ortholog, trehalose synthase long chain (TSL1) polypeptide, a polypeptide encoded by a tsl1 ortholog, neutral trehalase 1 (NTH1), a polypeptide encoded by a nth1 ortholog, neutral trehalase 2 (NTH2), a polypeptide encoded by a nth2 ortholog, acid trehalase 1 (ATH1), a polypeptide encoded by a ath1 ortholog, hexokinase 1 (HXK1), a polypeptide encoded by a hxk1 ortholog, hexokinase 2 (HXK2), a polypeptide encoded by a hxk2 ortholog, glucokinase 1 (GLK1), a polypeptide encoded by a glk1 ortholog, phosphoglucomutase 1 (PGM1), a polypeptide encoded by a pgm1 ortholog, phosphoglucomutase 2 (PGM2), a polypeptide encoded by a pgm2 ortholog, glycogen phosphorylase 1 (GPH1), a polypeptide encoded by a gph1 ortholog, UDP-glucose pyrophosphorylase (UGP1), a polypeptide encoded by a ugp1 ortholog, glycogen synthase 1 (GSY1), a polypeptide encoded by a gsy1 ortholog, glycogen synthase 2 (GSY2) and/or a polypeptide encoded by a gsy2 ortholog.