Inspired by the 1944 Avery, McLeod and McCarty demonstration that that DNA is the material responsible for bacterial transformation, medical student Joshua Lederberg began to investigate his hypothesis that, contrary to prevailing opinion, bacteria did not simply pass down exact copies of genetic information, making all cells in a lineage essentially clones. After making little progress at Columbia, Lederberg wrote to geneticist Edward Tatum, his post-doctoral mentor, proposing a collaboration. In 1946 Lederberg took a leave of absence to study under Tatum at Yale University. Later that year Lederberg and Tatum showed that the bacterium Escherichia coli entered a sexual phase during which it could share genetic information through bacterial conjugation. In their very brief paper (less than one page) the authors reported the discovery of sexual processes in the reproduction of bacteria: "Gene Recombination in Escherichia coli," Nature 158 (1946) 558. In 1947 they expanded this report in a much longer paper: Tatum & Lederberg, "Gene Recominbation in the Bacterium Escherichia coli," J. Bacteriol. (1947) 53, 673-684.
Lederberg and Tatum's one-page paper published in Nature in 1946 remains under copyright, but the very brief text may be read online in its reprint in Peters, Classic Papers in Genetics (1959) 192-194.