Importance of the Aspergillus fumigatus Mismatch Repair Protein Msh6 in Antifungal Resistance Development.

One of the systems responsible for the recognition and repair of mistakes occurring during cell replication is the DNA mismatch repair (MMR) system. Two major protein complexes constitute the MMR pathway: MutS and MutL. Here, we investigated the possible relation of four A. fumigatus MMR genes ( msh 2, msh 6, pms 1, and mlh 1) with the development of azole resistance related to the phenomenon of multi-drug resistance. We examined the MMR gene variations in 163 Aspergillus fumigatus genomes. Our analysis showed that genes msh 2, pms 1, and mlh 1 have low genetic variability and do not seem to correlate with drug resistance. In contrast, there is a nonsynonymous mutation (G240A) in the msh 6 gene that is harbored by 42% of the strains, most of them also harboring the TR 34 /L98H azole resistance mechanism in cyp 51A. The msh 6 gene was deleted in the aku B KU80 A. fumigatus strain, and the ∆ msh 6 isolates were analyzed for fitness, azole susceptibility, and virulence capacity, showing no differences compared with the aku B KU80 parental strain. Wild-type msh 6 and Δ msh 6 strains were grown on high concentrations of azole and other non-azole fungicides used in crop protection. A 10- and 2-fold higher mutation frequency in genes that confer resistance to boscalid and benomyl, respectively, were observed in Δ msh 6 strains compared to the wild-type. This study suggests a link between Msh6 and fungicide resistance acquisition.