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Antimicrobial Agents and Chemotherapy, January 2004, p. 229-235, Vol. 48, No. 1
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.1.229-235.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Antimicrobial Activity of a Chelatable Poly(Arginyl-Histidine) Produced by the Ergot Fungus Verticillium kibiense

Masanobu Nishikawa^* and Ken'ichi Ogawa

Research Institute for Biological Sciences, Okayama (RIBS), 7549-1 Kayo-cho, Okayama 716-1241, Japan

Received 12 May 2003/ Returned for modification 24 August 2003/ Accepted 7 October 2003

We have recently developed a convenient method of screening a broad range of microorganisms that produce -poly-L-lysine (M. Nishikawa and K. Ogawa, Appl. Environ. Microbiol. 68:3575-3581, 2002). Using this method, we found an ergot fungus that secretes a charged polypeptide other than -poly-L-lysine. It was identified as a new species on the basis of its 28S rRNA sequence and was named Verticillium kibiense (formerly Epichloe kibiensis). Peptide sequencing and mass spectrometry revealed that the polypeptide is a linear peptide composed of repeated units of arginyl-histidine. The numbers of repeated units were in most cases five and in some cases four or six. This peptide showed activity against a broad range of bacteria and fungi but lost its activity under conditions of high ionic strength. Zinc and copper ions specifically changed the circular dichroism spectra of the peptide and restored the antimicrobial activity from abrogation under high ionic conditions, although these ions had no reinforcing effect on antimicrobial activity when they were added to solutions at a low ionic strength. The peptide labeled with fluorescein was able to permeate the cell membranes of target microbes, but its ability to permeate cell membranes decreased under conditions of high ionic strength. This decreased ability was partially recovered specifically by the addition of zinc and copper ions. These results indicate that poly(arginyl-histidine) is a cationic polypeptide characterized by specific metal binding and resistance to salts.

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* Corresponding author. Mailing address: Research Institute for Biological Sciences, Okayama (RIBS), 7549-1 Kayo-cho, Okayama 716-1241, Japan. Phone: 81-866-56-9452. Fax: 81-866-56-9454. E-mail: mnishikawa{at}bio-ribs.com.

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Antimicrobial Agents and Chemotherapy, January 2004, p. 229-235, Vol. 48, No. 1
0066-4804/04/$08.00+0     DOI: 10.1128/AAC.48.1.229-235.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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