Public Health Laboratories Toronto, Public Health Ontario, Toronto, Ontario, Canada.
PLoS One. 2013;8(3):e59237. doi: 10.1371/journal.pone.0059237. Epub 2013 Mar 22.
Analysis of the population genetic structure of microbial species is of fundamental importance to many scientific disciplines because it can identify cryptic species, reveal reproductive mode, and elucidate processes that contribute to pathogen evolution. Here, we examined the population genetic structure and geographic differentiation of the sexual, dimorphic fungus Blastomyces dermatitidis, the causative agent of blastomycosis.
METHODOLOGY/PRINCIPAL FINDINGS: Criteria for Genealogical Concordance Phylogenetic Species Recognition (GCPSR) applied to seven nuclear loci (arf6, chs2, drk1, fads, pyrF, tub1, and its-2) from 78 clinical and environmental isolates identified two previously unrecognized phylogenetic species. Four of seven single gene phylogenies examined (chs2, drk1, pyrF, and its-2) supported the separation of Phylogenetic Species 1 (PS1) and Phylogenetic Species 2 (PS2) which were also well differentiated in the concatenated chs2-drk1-fads-pyrF-tub1-arf6-its2 genealogy with all isolates falling into one of two evolutionarily independent lineages. Phylogenetic species were genetically distinct with interspecific divergence 4-fold greater than intraspecific divergence and a high Fst value (0.772, P<0.001) indicative of restricted gene flow between PS1 and PS2. Whereas panmixia expected of a single freely recombining population was not observed, recombination was detected when PS1 and PS2 were assessed separately, suggesting reproductive isolation. Random mating among PS1 isolates, which were distributed across North America, was only detected after partitioning isolates into six geographic regions. The PS2 population, found predominantly in the hyper-endemic regions of northwestern Ontario, Wisconsin, and Minnesota, contained a substantial clonal component with random mating detected only among unique genotypes in the population.
CONCLUSIONS/SIGNIFICANCE: These analyses provide evidence for a genetically divergent clade within Blastomyces dermatitidis, which we use to describe a novel species, Blastomyces gilchristii sp. nov. In addition, we discuss the value of population genetic and phylogenetic analyses as a foundation for disease surveillance, understanding pathogen evolution, and discerning phenotypic differences between phylogenetic species.
分析微生物种的种群遗传结构对许多科学学科都至关重要，因为它可以识别隐种，揭示繁殖方式，并阐明有助于病原体进化的过程。在这里，我们检查了有性二态真菌皮炎芽生菌（Blastomyces dermatitidis）的种群遗传结构和地理分化，皮炎芽生菌是芽生菌病的病原体。
方法/主要发现：应用于从 78 株临床和环境分离株中获得的 7 个核基因座（arf6、chs2、drk1、fads、pyrF、tub1 和 its-2）的系统发育一致种系发生物种识别（GCPSR）标准，鉴定出两个以前未被识别的系统发育种。在所检查的七个单基因系统发育树中的四个（chs2、drk1、pyrF 和 its-2）中，支持将种 1（PS1）和种 2（PS2）分开，这两种在 chs2-drk1-fads-pyrF-tub1-arf6-its2 基因序列的联合系统发育树中也得到了很好的分化，所有分离株都属于两个进化独立的谱系之一。种系发生种在遗传上是不同的，种间分歧是种内分歧的四倍，Fst 值很高（0.772，P<0.001），表明 PS1 和 PS2 之间的基因流动受到限制。虽然没有观察到预期的单一自由重组种群的随机交配，但当分别评估 PS1 和 PS2 时，检测到了重组，表明存在生殖隔离。在北美各地分布的 PS1 分离株中，随机交配仅在将分离株划分为六个地理区域后才被检测到。PS2 种群主要存在于安大略省西北部、威斯康星州和明尼苏达州的高度流行地区，其中包含大量克隆成分，仅在种群中的独特基因型中检测到随机交配。
结论/意义：这些分析为皮炎芽生菌中的一个遗传上有差异的分支提供了证据，我们用它来描述一个新的种，即 Blastomyces gilchristii sp. nov.。此外，我们还讨论了种群遗传和系统发育分析作为疾病监测、了解病原体进化以及辨别种系发生种之间表型差异的基础的价值。
