Oxidative stress and the presence of bacteria increase gene expression of the antimicrobial peptide aclasin, a fungal CSαβ defensin in Aspergillus clavatus.

Holger Schäfer,Nessa Wang,Gabriela Contreras,Michael Wink

doi:10.7717/peerj.6290

Abstract

BackgroundAntimicrobial peptides (AMPs) represent a broad class of naturally occurring antimicrobial compounds. Plants, invertebrates and fungi produce various AMPs as, for example, defensins. Most of these defensins are characterised by the presence of a cysteine-stabilised α-helical and β-sheet (CSαβ) motif. The changes in gene expression of a fungal CSαβ defensin by stress conditions were investigated in Aspergillus clavatus. A. clavatus produces the CSαβ defensin Aclasin, which is encoded by the aclasin gene.MethodsAclasin expression was evaluated in submerged mycelium cultures under heat shock, osmotic stress, oxidative stress and the presence of bacteria by quantitative real-time PCR.ResultsAclasin expression increased two fold under oxidative stress conditions and in the presence of viable and heat-killed Bacillus megaterium. Under heat shock and osmotic stress, aclasin expression decreased.DiscussionThe results suggest that oxidative stress and the presence of bacteria might regulate fungal defensin expression. Moreover, fungi might recognise microorganisms as plants and animals do.

Highlights

Antimicrobial peptides (AMPs) are a diverse group of naturally occurring molecules that are produced by a wide range of organisms, both prokaryotes and eukaryotes
Strains and conditions of culture Aspergillus clavatus DSM 3410 and Bacillus megaterium DSM 32 were obtained from the German Collection of Microorganisms and Cell Cultures (DSMZ)
Aclasin expression during vegetative mycelium growth The aclasin gene (ACLA_006820) encodes Aclasin, a putative cysteine-stabilised a-helical and β-sheet (CSaβ) defensin produced by A. clavatus (Zhu, 2008)

Summary

Introduction

Antimicrobial peptides (AMPs) are a diverse group of naturally occurring molecules that are produced by a wide range of organisms, both prokaryotes and eukaryotes. Invertebrates and fungi produce various AMPs as, for example, defensins. Most of these defensins are characterised by the presence of a cysteine-stabilised a-helical and β-sheet (CSaβ) motif. The changes in gene expression of a fungal CSaβ defensin by stress conditions were investigated in Aspergillus clavatus. Methods: Aclasin expression was evaluated in submerged mycelium cultures under heat shock, osmotic stress, oxidative stress and the presence of bacteria by quantitative real-time PCR. Results: Aclasin expression increased two fold under oxidative stress conditions and in the presence of viable and heat-killed Bacillus megaterium. Discussion: The results suggest that oxidative stress and the presence of bacteria might regulate fungal defensin expression. Fungi might recognise microorganisms as plants and animals do

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