A genome-wide transcription analysis of a fungal riboflavin overproducer.

The production of many fine chemicals such as vitamins and amino acids is carried out in bioreactors using microorganisms. Usually, these strains are developed from wild-type organisms by classical mutation and selection. After several generations of strain improvement, no further enhancement can be achieved. Therefore, metabolic engineering (ME) is a rational approach to optimise such producer organisms beyond this point, or for starting all over from the beginning. Metabolic Engineering involves detailed analysis of the organism's metabolic and genetic properties, leading to the identification of new target genes. The fungal riboflavin overproducer Ashbya gossypii converts vegetable oil to vitamin B2 in a "one-step reaction". The productivity and selectivity of this microorganism have been optimised significantly over the years, first following a classical approach and now a rational one. The improvement is based on our understanding of vitamin B2 metabolism. We have been able to selectively enhance the pathways that are necessary for the formation of riboflavin and to inhibit those leading to unwanted side products. New targets for further improvements of this process have been found using a genome-wide transcript expression analysis; namely massive parallel signature sequencing (MPSS). With this analysis even completely unknown genes can be used for strain improvement.