The invention relates to an isolated, genetically modified microorganism, wherein compared to the wild type a) the idh1 and idp1 genes have been deleted or inactivated, and/or b) the sdh2 and sdh1 genes have been deleted or inactivated, and/or c) the PDC2 gene has been deleted or inactivated or is under the control of a promoter which can be suppressed or induced by exposure of the microorganism using an inductor substance, and/or d) one or more genes from the group consisting of ICL1, MLS1, ACS1 and MDH3 has been replaced or supplemented by a corresponding foreign gene or corresponding foreign genes from Crabtree-negative organisms, and to the uses thereof.