Bacterial DNA uptake and the evolution of sex

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Sexual reproduction poses a serious problem for evolutionary biologists. Its main consequence is to shuffle combinations of genes, but we do not know why this is beneficial. Comparison with bacteria can clarify the options dramatically-if bacteria have no equivalent to sex, then whatever problem sex solves for eukaryotes must be one that bacteria don't face. Bacteria do have processes that sometimes create new combinations of genes by moving DNA from one cell to another, but these processes likely have other, more important, functions. In particular, my research suggests that bacteria bring DNA fragments into their cells to use as food rather than as sources of new genes. To further test this hypothesis I propose to study DNA uptake by diverse bacteria. Although most bacteria will take up any DNA fragments they encounter (as expected if DNA is used as food), a few are more discriminating, preferring DNAs with sequence patterns typical of their own species. Some researchers argue that it disproves the food hypothesis because this specificity increases the likelihood of recombination, but we suspect that it is merely a byproduct of how the DNA-uptake proteins bind to DNA. PhD and undergraduate students will together test seven diverse species of bacteria, measuring whether the cells have any preference for DNA from their own species and whether their DNA uptake proteins bind to some DNA sequences better than others. This work will provide unusually broad training in molecular and evolutionary biology, microbiology, genomics and bioinformatics. Finding common uptake bias without preference for conspecific DNA would strengthen our hypothesis by showing that uptake bias is not usually a mate recognition signal, indicating that recombination is not directly selected in these bacteria. Finding that uptake biases are always accompanied by self-specificity would weaken our hypothesis. Either outcome would be a significant advance, strengthening the already major contributions of Canadian scientists to the problem of the evolution of sex.