Novozhilov Artem S, Karev Georgy P, Koonin Eugene V
National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Maryland, USA.
Mol Biol Evol. 2005 Aug;22(8):1721-32. doi: 10.1093/molbev/msi167. Epub 2005 May 18.
We describe a stochastic birth-and-death model of evolution of horizontally transferred genes in microbial populations. The model is a generalization of the stochastic model described by Berg and Kurland and includes five parameters: the rate of mutational inactivation, selection coefficient, invasion rate (i.e., rate of arrival of a novel sequence from outside of the recipient population), within-population horizontal transmission ("infection") rate, and population size. The model of Berg and Kurland included four parameters, namely, mutational inactivation, selection coefficient, population size, and "infection." However, the effect of "infection" was disregarded in the interpretation of the results, and the overall conclusion was that horizontally acquired sequences can be fixed in a population only when they confer a substantial selective advantage onto the recipient and therefore are subject to strong positive selection. Analysis of the present model in different domains of parameter values shows that, as long as the rate of within-population horizontal transmission is comparable to the mutational inactivation rate and there is even a low rate of invasion, horizontally acquired sequences can be fixed in the population or at least persist for a long time in a substantial fraction of individuals in the population even when they are neutral or slightly deleterious. The available biological data strongly suggest that intense within-population and even between-populations gene flows are realistic for at least some prokaryotic species and environments. Therefore, our modeling results are compatible with the notion of a pivotal role of horizontal gene transfer in the evolution of prokaryotes.
我们描述了一个微生物群体中水平转移基因进化的随机生死模型。该模型是对伯格和库兰德所描述的随机模型的推广，包含五个参数：突变失活率、选择系数、入侵率（即新序列从受体群体外部进入的速率）、群体内水平转移（“感染”）率以及群体大小。伯格和库兰德的模型包含四个参数，即突变失活、选择系数、群体大小和“感染”。然而，在结果解释中忽略了“感染”的影响，总体结论是水平获得的序列只有在赋予受体显著的选择优势并因此受到强烈正选择时才能在群体中固定下来。对本模型在不同参数值范围内的分析表明，只要群体内水平转移率与突变失活率相当，并且即使入侵率很低，水平获得的序列也能够在群体中固定下来，或者至少在群体中相当一部分个体中长期存在，即便它们是中性的或略有有害。现有的生物学数据有力地表明，至少对于某些原核生物物种和环境而言，群体内甚至群体间的强烈基因流动是现实存在的。因此，我们的建模结果与水平基因转移在原核生物进化中起关键作用这一观点相符。
