Chromosome-Scale Genome Analysis Reveals Locus-Specific Disruption of the Citrinin-Associated Region in a Furu-Derived Monascus ruber Strain BC20

Monascus species are widely used in traditional fermented foods for pigment and flavor formation, but citrinin contamination remains a major safety concern that limits broader food applications. Therefore, this study aimed to evaluate the citrinin risk of a furu-derived Monascus ruber strain, BC20, by integrating phenotypic screening across food-relevant matrices with genome-resolved analysis. After 14 days of cultivation across eight matrices, including fungal media as well as dairy-, cereal-, and bran-based substrates, citrinin was not detected by immunoaffinity cleanup combined with HPLC–FLD (LOD, 4 μg/kg; LOQ, 12 μg/kg). To investigate the genetic basis of this phenotype, we generated a chromosome-scale genome assembly for BC20 and conducted comparative analyses across a total of 19 Monascus genomes. ANI analysis and phylogenomic inference consistently placed BC20 within the ruber–pilosus clade. Comparative synteny analysis showed that the citrinin-associated locus in BC20 no longer retained an intact cluster configuration but instead exhibited a remnant-locus architecture, and similar patterns were also observed in several related genomes from the same clade. By contrast, the monacolin K (mk) locus remained syntenically conserved in BC20, supporting locus-specific structural disturbance rather than assembly-derived pseudo-absence. Additionally, its antifungal susceptibility was determined. Overall, BC20 represents a M. ruber candidate strain with undetectable citrinin, and this study provides a practical analytical framework for citrinin risk screening in food-related Monascus isolates.