Abstract
Aspergillus flavipes has received considerable interest due to its potential to produce therapeutic enzymes involved in sulfur amino acid metabolism. In natural habitats, A. flavipes survives under sulfur limitations by mobilizing endogenous and exogenous sulfur to operate diverse cellular processes. Sulfur limitation affects virulence and pathogenicity, and modulates proteome of sulfur assimilating enzymes of several fungi. However, there are no previous reports aimed at exploring effects of sulfur limitation on the regulation of A. flavipes sulfur metabolism enzymes at the transcriptional, post-transcriptional and proteomic levels. In this report, we show that sulfur limitation affects morphological and physiological responses of A. flavipes. Transcription and enzymatic activities of several key sulfur metabolism genes, ATP-sulfurylase, sulfite reductase, methionine permease, cysteine synthase, cystathionine β- and γ-lyase, glutathione reductase and glutathione peroxidase were increased under sulfur starvation conditions. A 50 kDa protein band was strongly induced by sulfur starvation, and the proteomic analyses of this protein band using LC-MS/MS revealed similarity to many proteins involved in the sulfur metabolism pathway.
Highlights
Aspergillus flavipes is a nutritionally facultative fungus, widely distributed in the rhizosphere [1] and as an endophyte in various plants [2]
To investigate effect of sulfur (S) starvation and re-supply of various S sources on morphological and physiological characteristics of A. flavipes, fungal spores were first grown in sulfur-free liquid medium [27], and subsequently transferred to media containing various sulfur sources: MgSO4, L-Methionine, L-Cysteine, L-Cystine or Glutathione
Effect of sulfur starvation and of different S sources on the physiology of A. flavipes was assessed by comparing fungal fresh weight, intracellular and extracellular proteins, and total glutathione in starved and non-starved control cultures (Fig 2)
Summary
Aspergillus flavipes is a nutritionally facultative fungus, widely distributed in the rhizosphere [1] and as an endophyte in various plants [2]. A. flavipes has recently been explored for the production of sulfur amino acid metabolizing enzymes such as L-methionine γ-lyase, homocysteine γ-lyase, cystathionine γ-lyase, and glutathione-homocystine oxidoreductase [3,4,5,6,7,8]. These enzymes exhibit a remarkable pharmaceutical potential for use against cardiovascular diseases and cancer. Endophytic isolates of A. flavipes from marine plants were shown to produce secondary metabolites including spiroquinazolines, cerebrosides, isobenzofurans, cytochalasins and butyrolactones with broad range antimicrobial, cytotoxic and antiviral activities [1, 9,10,11,12]. Gene expression and metabolomic activities of A. flavipes are affected by the availability of nutrients, especially exogenous sulfur, which is directly incorporated into L-methionine, PLOS ONE | DOI:10.1371/journal.pone.0144304 December 3, 2015
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