Abstract：
SUMMARYEvery human being is presumed to be infected by the fungus Pneumocystis jirovecii at least once in his or her lifetime. This fungus belongs to a large group of species that appear to exclusively infect mammals, with P. jirovecii being the only one known to cause disease in humans. The mystery of P. jirovecii origin and speciation is just beginning to unravel. Here, we provide a review of the major steps of P. jirovecii evolution. The Pneumocystis genus likely originated from soil or plant-associated organisms during the period of Cretaceous ~165 million years ago and successfully shifted to mammals. The transition coincided with a substantial loss of genes, many of which are related to the synthesis of nutrients that can be scavenged from hosts or cell wall components that could be targeted by the mammalian immune system. Following the transition, the Pneumocystis genus cospeciated with mammals. Each species specialized at infecting its own host. Host specialization is presumably built at least partially upon surface glycoproteins, whose protogene was acquired prior to the genus formation. P. jirovecii appeared at ~65 million years ago, overlapping with the emergence of the first primates. P. jirovecii and its sister species P. macacae, which infects macaques nowadays, may have had overlapping host ranges in the distant past. Clues from molecular clocks suggest that P. jirovecii did not cospeciate with humans. Molecular evidence suggests that Pneumocystis speciation involved chromosomal rearrangements and the mounting of genetic barriers that inhibit gene flow among species.
摘要：
总结假定每个人一生中至少有一次被真菌肺孢子虫感染。这种真菌属于一大群似乎只感染哺乳动物的物种，吉罗韦西是唯一已知会导致人类疾病的人。P.jirovecii起源和物种形成之谜刚刚开始揭开。这里,我们对吉罗韦西氏菌进化的主要步骤进行了综述。肺孢子虫属可能起源于白垩纪〜1.65亿年前的土壤或植物相关生物，并成功转移到哺乳动物。这个转变恰逢基因大量丧失,其中许多与营养素的合成有关，这些营养素可以从宿主或细胞壁成分中清除，而这些成分可以被哺乳动物的免疫系统所靶向。过渡后,与哺乳动物共种的肺孢子虫属。每个物种都专门感染自己的宿主。宿主特化可能至少部分建立在表面糖蛋白上，其原始基因是在属形成之前获得的。P.jirovecii出现在6500万年前，与第一批灵长类动物的出现重叠。P.jirovecii和它的姐妹物种P.macacae，现在感染猕猴，在遥远的过去，可能有重叠的宿主范围。来自分子钟的线索表明，P.jirovecii不与人类共种。分子证据表明，肺孢子虫物种形成涉及染色体重排和抑制物种间基因流动的遗传障碍的建立。
