Killing of M. catarrhalis O35E by M. catarrhalis E22 carrying pLQ510. Test strains and indicator strains were grown on BHI agar plates as described in Materials and Methods. Panels: A, O35E test strain on O35E indicator; B, O35E test strain on E22 indicator; C, E22 test strain on O35E indicator; D, E22 test strain on E22 indicator. The white arrow in panel C indicates the zone of killing of the indicator strain by the test strain. Panel E, schematic of pLQ510 indicating the four ORFs located in the mcb locus. The nucleotide sequence of pLQ510 is available at GenBank under accession no. AF129811. The positions of the restriction sites used to insert kanamycin resistance cassettes in the mcbB and mcbC genes are indicated.