Microcin 25, a novel antimicrobial peptide produced by Escherichia coli

Abstract

Microcin 25, a peptide antibiotic excreted by an Escherichia coli strain isolated from human feces, was purified to homogeneity and characterized. Composition analysis and data from gel ifitration indicated that microcin 25 may contain 20 amino acid residues. It has a blocked amino-terminal end. Microcin synthesis and immunity are plasmid determined, and the antibiotic was produced in minimal medium when the cultures entered the stationary phase of growth. The peptide appears to interfere with cell divrision, since susceptible cells filamented when exposed to it. This response does not seem to be mediated by the SOS system.Microcins are a miscellaneous group of low-molecularweight antibiotics produced by a number of enterobacteria, mostly Escherichia coli strains (2). Several features distinguish them from the more widely studied colicins. Microcins are considerably smaller, their synthesis is neither lethal nor controlled by the SOS regulatory circuit, and synthesis takes place during the stationary phase of growth (with the possible exception of microcin E492 from Kiebsiella pneumoniae, the production of which starts in the exponential phase) (3). Moreover, colicins are bactericidal proteins, whereas microcins may exhibit bactericidal or bacteriostatic modes of action. At least for the most extensively characterized microcins, B17 and C7, the genetic systems involved in their production and immunity are considerably more complex than the contiguous arrangement of three genes (synthesis, immunity, and release via lysis) which is a common feature of colicin-producing plasmids (16,31,34). Like those of colicins, the genetic determinants for microcins seem to be invariably plasmid borne. However, Lavinia et al. have recently described a novel member of the family, microcin H47, which is chromosomally encoded (24).Microcins are a promising model system for the study of peptide transport mechanisms and the regulation of gene expression in nonproliferating cells. Studies of them may also contribute to a deeper understanding of the structurefunction relationships of antimicrobial peptides.This article introduces the study of a novel peptide antibiotic which is excreted into the culture medium by a fecal strain of E. coli. We have called it microcin 25 (Mcc25). The purification, initial biochemical characterization, and some properties of Mcc25 are reported. Also, we present results suggesting that it can act as a cell division inhibitor. MATERIALS AND METHODSBacterial strains. The bacteria used in this work are listed in Table 1. All strains are derivatives of E. coli K-12 except for AY25, the natural E. coli producer of Mcc25, and AY29, its nonproducing plasmid-cured derivative. Strain AY25 was isolated in our laboratory from the feces of a newborn infant, as described previously (3).Media. LB rich and M63 minimal media have been de-* Corresponding author.scribed by Miller (29). Minimal medium was supplemented with 0.2% of the specified carbon source, thiamine (1 ,g/ml), and, when appropriate, L-amino acids (20 ,ug/m...

Investigation into the mechanism of action of the antimicrobial peptides Os and Os-C derived from a tick defensin

“…However, no morphological changes to the septa were observed with TEM. The peptides PR-39 [29], PR-26 [29], indolicidin [31] and microcin [28] were previously found to cause filamentation which may be caused by the inhibition or alteration of membrane proteins required for septum formation [4]. Sochaki and colleagues previously found that fluorescently labeled LL-37 more readily entered E. coli cells at the septal regions of dividing cells [30].…”

Topoisomer Differentiation of Molecular Knots by FTICR MS: Lessons from Class II Lasso Peptides

“…They form three classes depending on the absence (class II) or presence of one (class III) or two (class I) disulfide bridges that further stabilize the structure [6]. They exhibit a variety of biological activities, involving enzyme inhibition, receptor antagonism, antimicrobial or anti-HIV activities (see Table 1 for class II lasso peptides) [5,[7][8][9][10][11][12]. Their compact structure confers to lasso peptides a great resistance to denaturing conditions and certain proteases.…”

The iron–siderophore transporter FhuA is the receptor for the antimicrobial peptide microcin J25: role of the microcin Val11–Pro16 β-hairpin region in the recognition mechanism

“…Therefore they are considered to play a major role in the regulation of microbial competition within the intestinal flora. MccJ25 (microcin J25) is naturally secreted by the faecal Escherichia coli AY25 strain [1]. The 21-residue mature MccJ25 (2.1 kDa) was isolated from culture supernatants [2].…”