Bacterial DNA uptake and the evolution of sex

有性生殖对进化生物学家来说是一个严重的问题。 它的主要后果是打乱基因组合，但我们不知道为什么这是有益的。 与细菌的比较可以戏剧性地澄清选择如果细菌没有与性等价的东西，那么性为真核生物解决的任何问题都必须是细菌不面临的问题。细菌确实有一些过程，有时会通过将DNA从一个细胞转移到另一个细胞来创造新的基因组合，但这些过程可能还有其他更重要的功能。 特别是，我的研究表明，细菌将DNA片段带入细胞中用作食物，而不是作为新基因的来源。** 为了进一步验证这一假设，我建议研究不同细菌的DNA摄取。 尽管大多数细菌会吸收它们遇到的任何DNA片段（如果DNA被用作食物，这是预期的），但有一些细菌更有鉴别力，更喜欢具有自己物种典型序列模式的DNA。一些研究人员认为，它反驳了食物假说，因为这种特异性增加了重组的可能性，但我们怀疑它只是DNA摄取蛋白如何与DNA结合的副产品。 博士生和本科生将一起测试七种不同的细菌，测量细胞是否对来自自己物种的DNA有任何偏好，以及它们的DNA摄取蛋白是否比其他人更好地与某些DNA序列结合。这项工作将在分子和进化生物学、微生物学、基因组学和生物信息学方面提供不同寻常的广泛培训。 发现共同的摄取偏差没有偏好同种DNA将加强我们的假设，显示摄取偏差通常不是配偶识别信号，表明重组不是直接选择在这些细菌。 发现摄取偏差总是伴随着自我特异性会削弱我们的假设。 无论哪种结果，都将是一个重大的进步，加强加拿大科学家对性别进化问题的重大贡献。

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.********