Genomic analysis of a riboflavin-overproducing Ashbya gossypii mutant isolated by disparity mutagenesis

Abstract

Background: Ashbya gossypii naturally overproduces riboflavin and has been utilized for industrial riboflavin production. To improve riboflavin production, various approaches have been developed. In this study, to investigate the change in metabolism of a riboflavin-overproducing mutant, namely, the W122032 strain (MT strain) that was isolated by disparity mutagenesis, genomic analysis was carried out. Results: In the genomic analysis, 33 homozygous and 1377 heterozygous mutations were detected. Among these heterozygous mutations, the proportion of mutated reads in each gene was different, ranging from 21 to 75%. These results suggest that the MT strain exhibits a mixture of diploidy, triploidy and tetraploidy, or contains multiple nuclei containing different mutations. We tried to isolate haploid spores from the MT strain to prove it ploidy, but these spores were never isolated. This result indicate MT strain does not produce its spores. Homozygous and heterozygous mutations were found in genes encoding enzymes involved in amino acid metabolism, the TCA cycle, purine and pyrimidine nucleotide metabolism and the DNA mismatch repair system. Especially, genes encoding enzymes in mitochondria had many homozygous and heterozygous mutations intensively. These results suggest that the overproduction of riboflavin in the MT strain may be associated with mitochondrial dysfunction. Conclusion: This study provides new insights into riboflavin production in A. gossypii and the usefulness of disparity mutagenesis for the creation of new types of mutants for metabolic engineering.