Nutrient Excess Triggers the Expression of the Antifungal Protein PAFB.

Nutrient limitation and nonfavorable growth conditions have been suggested to be major triggers for the expression of small, cysteine-rich antimicrobial proteins (AMPs) of fungal origin, e.g., the antifungal protein (PAF), the antifungal protein (AFP), the antifungal protein (AnAFP). Therefore, these AMPs have been considered to be fungal secondary metabolite products. In contrast, the present study revealed that the expression of the PAF-related AMP antifungal protein B (PAFB) is strongly induced under nutrient excess during the logarithmic growth phase, whereas PAFB remained under the detection level in the supernatant of cultures grown under nutrient limitation. The efficiency of the -promoter to induce PAFB expression was compared with that of two promoters that are well established for recombinant protein production: the -promoter and the xylose-inducible promoter of the xylanase gene, . The inducibility of the -promoter was superior to that of the -promoter yielding comparable PAFB amounts as under the regulation of the -promoter. We conclude that (i) differences in the expression regulation of AMPs suggest distinct functional roles in the producer beyond their antifungal activity; and (ii) the -promoter is a promising tool for recombinant protein production in , as it guarantees strong gene expression with the advantage of inducibility.