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Background Aspergillus niger is a ubiquitous filamentous fungus widely employed as a cell factory thanks to its abilities to produce a wide range of organic acids and enzymes. Due to its economic importance and its role as model organism to study fungal fermentation, its genome was one of the first Aspergillus genomes to be sequenced in 2007. Nowadays, the genome sequences of at least five other A. niger strains are available. These, however, do not include the neotype strain CBS 554.65. Results In this study, the genome of CBS 554.65 was sequenced with PacBio. A high-quality nuclear genome sequence consisting of 17 contigs with a N50 value of 4.07 Mbp was obtained. The sequencing covered all the 8 centromeric regions of the chromosomes. In addition, a complete circular mitochondrial DNA assembly was obtained. In silico analyses revealed the presence of a MAT1-2-1 gene in this genome, contrary to the so far sequenced A. niger strains, which all contain a MAT1-1-1 gene. An alignment at the MAT locus showed a different position of the MAT1-1-1 gene of ATCC 1015 compared to the MAT1-2-1 gene of CBS 554.65, relative to the surrounding genes. In addition, 24 other sequenced isolates of A. niger showed a 1:1 ratio of MAT1-1 and MAT1-2 loci. While the genetic organization of the MAT1-2 locus of CBS 554.65 is similar to what is found in other aspergilli, the genetic organization of the MAT1-1 locus is flipped in all sequenced strains. Conclusions This study, besides providing a high-quality genome sequence of an important A. niger strain, suggests the occurrence of genetic flipping or switching events at the MAT1-1 locus of A. niger. These results provide new insights in the mating system of A. niger and could contribute to the investigation and potential discovery of sexuality of this so far asexual fungal species. |
