科学家发现一种存在于全世界海洋中的耐恶劣环境的微生物拥有一种新颖的逃脱病毒攻击的策略:它在生命的不同阶段之间转换。
一种名为Emiliana huxleyi的单细胞浮游植物身披碳酸钙的盔甲,而且在海洋-大气二氧化碳系统中扮演着一个重要的角色,它拥有一种大起大落的生活史。E. huxleyi的暴发是如此的巨大,以至于从太空中可以看到海洋上的一片蓝绿色区域。它的衰落是由病毒感染造成的,而且几乎能消灭掉这种微生物。Miguel Frada及其同事报告说,这种微生物从它熟悉的“二倍体”生命阶段(拥有染色体的两份拷贝)转变到了一个让病毒无法攻击的“单倍体”阶段(类似于精细胞和卵细胞)。这种单倍体阶段让E. huxleyi袖手旁观病毒的攻击,直到病毒消退。
这组作者探索了实验室中单一和混合的二倍体和单倍体群落如何对病毒做出响应。单倍体阶段的生长没有受到注入病毒的影响;二倍体的E. huxleyi几乎被灭绝了。然而,一个新的单倍体细胞群落从残余的细胞中诞生,这组科学家怀疑,单倍体细胞和多倍体细胞外壳之间差异是免疫力的关键。(生物谷Bioon.com)
生物谷推荐原始出处:
PNAS published September 29, 2008, doi:10.1073/pnas.0807707105
The “Cheshire Cat” escape strategy of the coccolithophore Emiliania huxleyi in response to viral infection
Miguel Frada, Ian Probert, Michael J. Allen, William H. Wilson, and Colomban de Vargas
The coccolithophore Emiliania huxleyi is one of the most successful eukaryotes in modern oceans. The two phases in its haplodiploid life cycle exhibit radically different phenotypes. The diploid calcified phase forms extensive blooms, which profoundly impact global biogeochemical equilibria. By contrast, the ecological role of the noncalcified haploid phase has been completely overlooked. Giant phycodnaviruses (Emiliania huxleyi viruses, EhVs) have been shown to infect and lyse diploid-phase cells and to be heavily implicated in the regulation of populations and the termination of blooms. Here, we demonstrate that the haploid phase of E. huxleyi is unrecognizable and therefore resistant to EhVs that kill the diploid phase. We further show that exposure of diploid E. huxleyi to EhVs induces transition to the haploid phase. Thus we have clearly demonstrated a drastic difference in viral susceptibility between life cycle stages with different ploidy levels in a unicellular eukaryote. Resistance of the haploid phase of E. huxleyi provides an escape mechanism that involves separation of meiosis from sexual fusion in time, thus ensuring that genes of dominant diploid clones are passed on to the next generation in a virus-free environment. These “Cheshire Cat” ecological dynamics release host evolution from pathogen pressure and thus can be seen as an opposite force to a classic “Red Queen” coevolutionary arms race. In E. huxleyi, this phenomenon can account for the fact that the selective balance is tilted toward the boom-and-bust scenario of optimization of both growth rates of calcifying E. huxleyi cells and infectivity of EhVs.