Current methodologies in genetics and microbiology enable researchers to influence metabolic pathways of microbial cells in many directions. Beside the academic interest in investigating fundamental functions in metabolic pathways, commercial production of valuable compounds by microbial hosts is state of the art. For example, such products include enzymes (lipases, proteases, phytases), therapeutic agents (insulin, antibodies), bulk chemicals (lysine, glutamate, citric acid), or the microbial cells themselves (used in brewing or milk processing), with therapeutic agents probably the fastest growing market.…