Harnessing natural transformation in Actinobacillus pleuropneumoniae: a simple method for allelic replacements.

We have investigated the use of a natural transformation protocol to introduce mutations into Actinobacillus pleuropneumoniae serotypes 1 and 5b. For both strains tested, we recovered 1 in 10(8) transformants during culture in rich medium, a result that was independent of the growth phase. This low frequency of transformation of A. pleuropneumoniae did not increase when bacteria were grown under conditions known to be optimal for induction of competence in Haemophilus influenzae. Using linearised plasmid DNA containing a kanamycin cassette inserted into the sodC gene of A. pleuropneumoniae serotype 1, we showed that natural transformation can be used as a simple method for introducing allele replacements into this bacterium, and can be used to transfer mutations from one serotype to another.