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Applied and Environmental Microbiology, June 2004, p. 3506-3511, Vol. 70, No. 6
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.6.3506-3511.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

The Weak Acid Preservative Sorbic Acid Inhibits Conidial Germination and Mycelial Growth of Aspergillus niger through Intracellular Acidification

Andrew Plumridge,1 Stephan J. A. Hesse,2 Adrian J. Watson,1 Kenneth C. Lowe,1 Malcolm Stratford,3 and David B. Archer1*

School of Biology, University of Nottingham, Nottingham NG7 2RD,1 Microbiology Section, Unilever R&D, Sharnbrook, Bedford MK44 1LQ United Kingdom,3 Department of Biophysics, Wageningen University, 6703 HA Wageningen, The Netherlands2

Received 20 November 2003/ Accepted 9 February 2004

The growth of the filamentous fungus Aspergillus niger, a common food spoilage organism, is inhibited by the weak acid preservative sorbic acid (trans-trans-2,4-hexadienoic acid). Conidia inoculated at 105/ml of medium showed a sorbic acid MIC of 4.5 mM at pH 4.0, whereas the MIC for the amount of mycelia at 24 h developed from the same spore inoculum was threefold lower. The MIC for conidia and, to a lesser extent, mycelia was shown to be dependent on the inoculum size. A. niger is capable of degrading sorbic acid, and this ability has consequences for food preservation strategies. The mechanism of action of sorbic acid was investigated using 31P nuclear magnetic resonance (NMR) spectroscopy. We show that a rapid decline in cytosolic pH (pHcyt) by more than 1 pH unit and a depression of vacuolar pH (pHvac) in A. niger occurs in the presence of sorbic acid. The pH gradient over the vacuole completely collapsed as a result of the decline in pHcyt. NMR spectra also revealed that sorbic acid (3.0 mM at pH 4.0) caused intracellular ATP pools and levels of sugar-phosphomonoesters and -phosphodiesters of A. niger mycelia to decrease dramatically, and they did not recover. The disruption of pH homeostasis by sorbic acid at concentrations below the MIC could account for the delay in spore germination and retardation of the onset of subsequent mycelial growth.

* Corresponding author. Mailing address: School of Biology, University of Nottingham, University Park, Nottingham, NG7 2RD, United Kingdom. Phone: 44 115 951 3313. Fax: 44 115 951 3251. E-mail: david.archer{at}nottingham.ac.uk.

Applied and Environmental Microbiology, June 2004, p. 3506-3511, Vol. 70, No. 6
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.6.3506-3511.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Bagar, T., Altenbach, K., Read, N. D., Bencina, M. (2009). Live-Cell Imaging and Measurement of Intracellular pH in Filamentous Fungi Using a Genetically Encoded Ratiometric Probe. Eukaryot Cell 8: 703-712 [Abstract] [Full Text]  
  • Melin, P., Stratford, M., Plumridge, A., Archer, D. B. (2008). Auxotrophy for uridine increases the sensitivity of Aspergillus niger to weak-acid preservatives. Microbiology 154: 1251-1257 [Abstract] [Full Text]  
  • Plumridge, A., Stratford, M., Lowe, K. C., Archer, D. B. (2008). The Weak-Acid Preservative Sorbic Acid Is Decarboxylated and Detoxified by a Phenylacrylic Acid Decarboxylase, PadA1, in the Spoilage Mold Aspergillus niger. Appl. Environ. Microbiol. 74: 550-552 [Abstract] [Full Text]  


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