Nutrient Excess Triggers the Expression of the Penicillium chrysogenum Antifungal Protein PAFB.

Anna Huber,Hannah Lerchster,Florentine Marx

doi:10.3390/microorganisms7120654

Anna Huber, Hannah Lerchster + Show 1 more

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https://doi.org/10.3390/microorganisms7120654

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Abstract

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 Penicillium chrysogenum antifungal protein (PAF), the Aspergillus giganteus antifungal protein (AFP), the Aspergillus niger 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 P. chrysogenum 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 pafB-promoter to induce PAFB expression was compared with that of two P. chrysogenum promoters that are well established for recombinant protein production: the paf-promoter and the xylose-inducible promoter of the xylanase gene, xylP. The inducibility of the pafB-promoter was superior to that of the xylP-promoter yielding comparable PAFB amounts as under the regulation of the paf-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 pafB-promoter is a promising tool for recombinant protein production in P. chrysogenum, as it guarantees strong gene expression with the advantage of inducibility.

Highlights

Fungi with sequenced genomes that belong to the class Eurotiomycetes contain at least one gene coding for antimicrobial proteins (AMPs) [1]
The present study revealed that the expression of the PAF-related AMP P. chrysogenum 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
To further substantiate our assumptions that PAFB is produced under favourable growth conditions, we investigated the production of secondary metabolites like penicillins, which are strongly induced under stress conditions when resources are low [30,31]

Summary

Introduction

Fungi with sequenced genomes that belong to the class Eurotiomycetes contain at least one gene coding for antimicrobial proteins (AMPs) [1]. These proteins are small in size (~6.5 kDa), cysteine-rich and amphipathic, and are secreted into the culture broth by their producer strains. Their compact disulfide-stabilized tertiary structure—containing five β-strands—renders them highly stable against adverse environmental conditions [2,3,4,5]. Most of them show no cytotoxicity to mammalian cells in vitro [10,11,15,16,17,18] and in vivo [16,19]

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