ICEA of M ycoplasma agalactiae : a new family of self‐transmissible integrative elements that confers conjugative properties to the recipient strain

Summary Horizontal gene transfer ( HGT ) is a major force of microbial evolution but was long thought to be marginal in mycoplasmas. In silico detection of exchanged regions and of loci encoding putative Integrative Conjugative Elements ( ICE ) in several mycoplasma genomes challenged this view, raising the prospect of these simple bacteria being able to conjugate. Using the model pathogen M ycoplasma agalactiae , we demonstrated for the first time that one of these elements, ICEA , is indeed self‐transmissible. As a hallmark of conjugative processes, ICEA transfers were DNase resistant and required viable cells. ICEA acquisition conferred ICE ‐negative strains with the new ability to conjugate, allowing the spread of ICEA . Analysis of transfer‐deficient mutants indicated that this process requires an ICEA ‐encoded lipoprotein of unknown function, CDS 14. Formation of a circular extrachromosomal intermediate and the subsequent chromosomal integration of ICEA involved CDS 22, an ICEA ‐encoded product distantly related to the ISLre 2 transposase family. Remarkably, ICEA has no specific or no preferential integration site, often resulting in gene disruptions. Occurrence of functional mycoplasma ICE offers these bacteria with a means for HGT , a phenomenon with far‐reaching implications given their minute‐size genome and the number of species that are pathogenic for a broad host‐range.