Genomic Signatures of Distributive Conjugal Transfer among

Distributive conjugal transfer (DCT) is a newly described mechanism of lateral gene transfer (LGT) that results in a mosaic transconju-gant structure, similar to the products of meiosis. We have tested popular LGT detection methods on whole-genome sequence data fromexperimentalDCT transconjugantsandused thebestperformingmethods tocomparegenomic signaturesofDCTwith thoseof LGTthroughnatural transformation, conjugativeplasmids,andmobilegeneticelements (MGE).WefoundthatDCTresults in transfer of larger chromosomal segments, that these segments are distributed more broadly around the chromosome, and that a greater proportion of the chromosome is affected by DCT than by other mechanisms of LGT. We used the best performing methods to characterizeLGT inMycobacteriumcanettii, themycobacterial speciesmostclosely relatedtoMycobacteriumtuberculosis. Patternsof LGT among M. canettii were highly distinctive. Gene flow appeared unidirectional, from lineages with minimal evidence of LGT to isolates with a substantial proportion (6–13%) of sites identified as recombinant. Among M. canettii isolates with evidence of LGT, recombinant fragments were larger and more evenly distributed relative to bacteria that undergo LGT through natural transforma-tion, conjugative plasmids, and MGE. Spatial bias in M. canettii was also unusual in that patterns of recombinant fragment sharing mirroredoverallphylogenetic structure.Basedontheproportionof recombinant sites, thesizeof recombinant fragments, their spatial distribution and lack of association with MGE, as well as unidirectionality of DNA transfer, we conclude that DCT is the predominant mechanism of LGT among M. canettii. Key words: lateral gene transfer, mycobacteria, Mycobacterium canettii, evolution