Identification of a bacteriocin and its cognate immunity factor expressed by Moraxella catarrhalis

Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, TX, USA.
BMC Microbiology (Impact Factor: 2.73). 09/2009; 9(1). DOI: 10.1186/1471-2180-9-207
Source: PubMed Central


Bacteriocins are antimicrobial proteins and peptides ribosomally synthesized by some bacteria which can effect both intraspecies and interspecies killing.

Moraxella catarrhalis strain E22 containing plasmid pLQ510 was shown to inhibit the growth of M. catarrhalis strain O35E. Two genes (mcbA and mcbB) in pLQ510 encoded proteins predicted to be involved in the secretion of a bacteriocin. Immediately downstream from these two genes, a very short ORF (mcbC) encoded a protein which had some homology to double-glycine bacteriocins produced by other bacteria. A second very short ORF (mcbI) immediately downstream from mcbC encoded a protein which had no significant similarity to other proteins in the databases. Cloning and expression of the mcbI gene in M. catarrhalis O35E indicated that this gene encoded the cognate immunity factor. Reverse transcriptase-PCR was used to show that the mcbA, mcbB, mcbC, and mcbI ORFs were transcriptionally linked. This four-gene cluster was subsequently shown to be present in the chromosome of several M. catarrhalis strains including O12E. Inactivation of the mcbA, mcbB, or mcbC ORFs in M. catarrhalis O12E eliminated the ability of this strain to inhibit the growth of M. catarrhalis O35E. In co-culture experiments involving a M. catarrhalis strain containing the mcbABCI locus and one which lacked this locus, the former strain became the predominant member of the culture after overnight growth in broth.

This is the first description of a bacteriocin and its cognate immunity factor produced by M. catarrhalis. The killing activity of the McbC protein raises the possibility that it might serve to lyse other M. catarrhalis strains that lack the mcbABCI locus, thereby making their DNA available for lateral gene transfer.

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    • "A study by Upton et al. (2001) described intra- and interspecies signaling between Streptococcus salivarius and S. pyogenes, mediated by SalA [46]. A single bacteriocin (McbC) has been described in M. catarrhalis, though the effect of this bacteriocin on GAS growth and virulence is not yet known [47]. "
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    • "Interestingly, the BC7 plasmid-associated contig sequence possesses homologs of the bacteriocin/immunity factor complex first described in the M. catarrhalis plasmid, pLQ510 [24,26]; however, annotation records for this region also identify an incomplete VirB-family type four secretion system (T4SS), multiple transposases and a resolvase not reported in pLQ510, suggesting that this sequence may represent either an extra-chromosomally maintained conjugative plasmid or an integrative and conjugative element (ICE; recently reviewed in [27]). Phage-associated annotations varied between strains, but comprised only 0.2% to 2.5% of all identified ORFs per genome, while transposon-associated annotations accounted for only 0.15% to 0.44% of all ORFs per genome. "
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