The role of ABC transporters from Aspergillus nidulans in protection against cytotoxic agents and in antibiotic production

This paper describes the characterization of atrC and atrD (ABC transporter s C and D), two novel ABC transporter-encoding genes from the filamentous f ungus Aspergillus nidulans, and provides evidence for the involvement of ar l D in multidrug transport and antibiotic production. BLAST analysis of the deduced amino acid sequences of AtrCp and AtrDp reveals high homology to A BC transporter proteins of the P-glycoprotein cluster. AtrDp shows a partic ularly high degree of identity to the amino acid sequence of AfuMdrlp, a pr eviously characterized ABC transporter from the human pathogen A. fumigatus . Northern analysis demonstrates an increase in transcript levels of atrC a nd atrD in fungal germlings upon treatment with natural toxic compounds and xenobiotics. The atrC gene has a high constitutive level of expression rel ative to atrD, which suggests its involvement in a metabolic function. Sing le knock-out mutants for atrC and atrD were generated by gene replacement u sing pyrG from A. oryzae as a selectable marker. Delta atrD mutants display a hypersensitive phenotype to compounds such as cycloheximide, the cyclosp orin derivative PSC 833, nigericin and valinomycin, indicating that AtrDp i s involved in protection against cytotoxic compounds. Energy-dependent effl ux of the azole-related fungicide fenarimol is inhibited by substrates of A trDp (e.g. PSC 833, nigericin and valinomycin), suggesting that AtrDp plays a role in efflux of this fungicide. Most interestingly, Delta atrD mutants display a decrease in penicillin production, measured indirectly as antimi crobial activity against Micrococcus luteus. These results suggest that ABC transporters may be involved in secretion of penicillin from fungal cells.