Identification of a bacteriocin and its cognate immunity factor expressed by Moraxella catarrhalis.
BACKGROUND
Bacteriocins are antimicrobial proteins and peptides ribosomally synthesized by some bacteria which can effect both intraspecies and interspecies killing.


RESULTS
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.


CONCLUSIONS
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.
Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, TX, USA. ahmed.s.attia@gmail.com
Ahmed S
AS
Attia
Jennifer L
JL
Sedillo
Todd C
TC
Hoopman
Wei
W
Liu
Lixia
L
Liu
Chad A
CA
Brautigam
Eric J
EJ
Hansen
D000595:Amino Acid Sequence; D000898:Antibiosis; D001430:Bacteriocins / Q000235:genetics* / Q000276:immunology; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D001936:Moraxella catarrhalis / Q000235:genetics* / Q000276:immunology; D005810:Multigene Family; D016366:Open Reading Frames; D010957:Plasmids; D017384:Sequence Deletion
D001430:Bacteriocins; D004269:DNA, Bacterial