Genome-Wide Survey of Donor Chromosomal Genes Involved in Trans-Kingdom Conjugation via the RP4-T4SS Machinery

Trans-kingdom conjugation (TKC)/inter-domain conjugation is a horizontal gene transfer phenomenon that transfers DNA from eubacteria to eukaryotes and archaebacteria via a type IV secretion system encoded in IncP1-type broad-host-range plasmids. Although TKC is considered a potential gene introduction tool, donor chromosomal genes that influence TKC efficiency have rarely been analyzed, hindering targeted donor breeding. To identify potential TKC-related genes on a donor chromosome, a genome-wide screening of TKC-deficient mutants was performed using a comprehensive collection of <i>Escherichia coli</i> gene knockout mutants (Keio collection) as donors and a <i>Saccharomyces cerevisiae</i> strain as a recipient. Out of 3884 mutants, two mutants (∆<i>aceE</i>, ∆<i>priA</i>) showed a severe decrease in TKC efficiency by more than two orders of magnitude but not in bacterial conjugation. The effect on TKC efficiency by the two mutants was partly recovered by a preculture with a fresh culture medium before the TKC reaction, regardless of the presence of antibiotics. These results suggest that no single chromosomal target gene is solely responsible for universally blocking IncP1-type conjugation by impeding its function. The results also suggest the existence of an unidentified recognition or transfer mechanism distinct from bacterial conjugation, highlighting the novel roles of <i>aceE</i> and <i>priA</i>.