Department of Molecular Cell and Developmental Biology, University of California, Santa Cruz, Santa Cruz, CA 95060; USA.
FEMS Microbiol Lett. 2019 Feb 1;366(3). doi: 10.1093/femsle/fnz013.
Symbiotic associations between bacteria and eukaryotes exhibit a range of transmission strategies. The rates and distributions of transmission modes have not been thoroughly investigated across associations, despite their consequences on symbiont and host evolution. To address this empirically, I compiled data from the literature on bacteria-multicellular eukaryote associations for which transmission mode data was available. Of the total 528 analyzed symbioses, 21.2% were strictly horizontally transmitted, 36.0% exhibited some form of mixed mode transmission and 42.8% were strictly vertically transmitted. Controlling for phylogenetically independent symbiosis events revealed modes were approximately equally distributed among the 113 independent associations, at 32.1%+/-0.57% horizontal, 37.8%+/-1.4% mixed mode and 31.1%+/-1.3% vertical transmission. Binning symbioses by environment revealed an abundance of vertical transmission on land and a lack of it in aquatic environments. The naturally occurring uneven distribution of taxa among environments prevented controlling for host/symbiont phylogeny. However, the results were robust over a large number of independently evolved associations, suggesting that many vertically transmitted bacteria are capable of mixed mode transmission and barriers exist that reduce the rate of horizontal transmission events. Thus, both the environment type and host/symbiont taxa influence symbiont transmission mode evolution.
细菌和真核生物之间的共生关系表现出一系列的传播策略。尽管它们对共生体和宿主进化有影响，但这些传播模式的速率和分布在不同的共生关系中并没有被彻底研究过。为了从经验上解决这个问题，我从文献中收集了有关细菌-多细胞真核生物共生关系的数据，这些数据中提供了传播模式的数据。在所分析的 528 个共生关系中，21.2%是严格水平传播的，36.0%表现出某种形式的混合模式传播，42.8%是严格垂直传播的。控制了系统发育独立的共生事件后，发现模式在 113 个独立的共生关系中大致均匀分布，水平传播模式占 32.1%+/-0.57%，混合模式传播模式占 37.8%+/-1.4%，垂直传播模式占 31.1%+/-1.3%。根据环境对共生关系进行分类，发现陆地环境中有大量的垂直传播，而水生环境中则缺乏垂直传播。由于自然环境中生物类群的分布不均，无法控制宿主/共生体的系统发育。然而，这些结果在大量独立进化的关联中是稳健的，这表明许多垂直传播的细菌能够进行混合模式传播，并且存在减少水平传播事件的速率的障碍。因此，环境类型和宿主/共生体的生物类群都会影响共生体传播模式的进化。
