NDLI: Single-cell, time-resolved study of the effects of the antimicrobial peptide alamethicin on Bacillus subtilis

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Weisshaar, James C. Barns, Kenneth J.
Description	Author Affiliation: Barns KJ ( Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA.); Weisshaar JC ( Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA)
Abstract	Alamethicin is a well-studied antimicrobial peptide (AMP) that kills Gram-positive bacteria. It forms narrow, barrel-stave pores in planar lipid bilayers. We present a detailed, time-resolved microscopy study of the sequence of events during the attack of alamethicin on individual, live Bacillus subtilis cells expressing GFP in the cytoplasm. At the minimum inhibitory concentration (MIC), the first observed symptom is the halting of growth, as judged by the plateau in measured cell length vs time. The data strongly suggest that this growth-halting event occurs prior to membrane permeabilization. Gradual degradation of the proton-motive force, inferred from a decrease in pH-dependent GFP fluorescence intensity, evidently begins minutes later and continues over about 5 min. There follows an abrupt permeabilization of the cytoplasmic membrane to the DNA stain Sytox Orange and concomitant loss of small osmolytes, causing observable cell shrinkage, presumably due to decreased turgor pressure. This permeabilization of the cytoplasmic membrane occurs uniformly across the entire membrane, not locally, on a timescale of 5 s or less. GFP gradually leaks out of the cell envelope, evidently impeded by the shrunken peptidoglycan layer. Disruption of the cell envelope by alamethicin occurs in stages, with larger and larger species permeating the envelope as time evolves over tens of minutes. Some of the observed symptoms are consistent with the formation of barrel-stave pores, but the data do not rule out “chaotic pore” or “carpet” mechanisms. We contrast the effects of alamethicin and the human cathelicidin LL-37 on B. subtilis.
ISSN	00063002
Journal	Biochimica et Biophysica Acta (BBA) - Reviews on Cancer
Issue Number	4
Volume Number	1858
Language	English
Publisher	Elsevier
Publisher Date	2016-04-01
Publisher Place	Netherlands
Access Restriction	Open
Subject Keyword	Alamethicin Pharmacology Anti-Infective Agents Chemistry Bacillus Subtilis Drug Effects Cell Membrane Antimicrobial Cationic Peptides Pathogenicity Lipid Bilayers Molecular Imaging Single-Cell Analysis Research Support, N.I.H., Extramural Biochemistry
Content Type	Text
Resource Type	Article

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