A genetically modified Saccharomyces cerevisiae including an active fermentation pathway producing 3-HP expresses an exogenous gene expressing the aminotransferase YhxA from Bacillus cereus AH1272 catalyzing a transamination reaction between beta-alanine and pyruvate to produce malonate semialdehyde. The yeast may also express a 3-hydroxyisobutyrate dehydrogenase (HIBADH) and a 3-hydroxypropanoate dehydrogenase (3-HPDH) and aspartate 1-decarboxylase. Additionally the yeast may express pyruvate carboxylase and aspartate aminotransferase.

Provided herein is a mutant microorganism containing a methylmalonyl-CoA reductase-encoding gene having an activity of converting methylmalonyl-CoA to methylmalonate semialdehyde and uses of the mutant microorganism. The mutant microorganism includes a gene encoding kingdom Archaea-derived methylmalonyl-CoA reductase.