Nielsen Kirsten, De Obaldia Anna L, Heitman Joseph
Department of Molecular Genetics and Microbiology, Research Drive, Duke University Medical Center, Durham, NC 27710, USA.
Eukaryot Cell. 2007 Jun;6(6):949-59. doi: 10.1128/EC.00097-07. Epub 2007 Apr 20.
The ecological niche that a species can occupy is determined by its resource requirements and the physical conditions necessary for survival. The niche to which an organism is most highly adapted is the realized niche, whereas the complete range of habitats that an organism can occupy represents the fundamental niche. The growth and development of Cryptococcus neoformans and Cryptococcus gattii on pigeon guano were examined to determine whether these two species occupy the same or different ecological niches. C. neoformans is a cosmopolitan pathogenic yeast that infects predominantly immunocompromised individuals, exists in two varieties (grubii [serotype A] and neoformans [serotype D]), and is commonly isolated from pigeon guano worldwide. By contrast, C. gattii often infects immunocompetent individuals and is associated with geographically restricted environments, most notably, eucalyptus trees. Pigeon guano supported the growth of both species, and a brown pigment related to melanin, a key virulence factor, was produced. C. neoformans exhibited prolific mating on pigeon guano, whereas C. gattii did not. The observations that C. neoformans completes the life cycle on pigeon guano but that C. gattii does not indicates that pigeon guano could represent the realized ecological niche for C. neoformans. Because C. gattii grows on pigeon guano but cannot sexually reproduce, pigeon guano represents a fundamental but not a realized niche for C. gattii. Based on these studies, we hypothesize that an ancestral Cryptococcus strain gained the ability to sexually reproduce in pigeon guano and then swept the globe.
一个物种能够占据的生态位是由其资源需求和生存所需的物理条件决定的。生物体最适应的生态位是实际生态位，而生物体能够占据的完整栖息地范围则代表基础生态位。研究了新型隐球菌和格特隐球菌在鸽粪上的生长和发育情况，以确定这两个物种占据的是相同还是不同的生态位。新型隐球菌是一种世界性致病酵母，主要感染免疫功能低下的个体，有两个变种（格鲁比变种[血清型A]和新型变种[血清型D]），在世界各地的鸽粪中普遍可分离到。相比之下，格特隐球菌常感染免疫功能正常的个体，且与地理上受限的环境有关，最显著的是桉树。鸽粪支持这两个物种的生长，并且产生了一种与黑色素有关的棕色色素，黑色素是一种关键的毒力因子。新型隐球菌在鸽粪上表现出大量交配，而格特隐球菌则没有。新型隐球菌能在鸽粪上完成生命周期而格特隐球菌不能这一观察结果表明，鸽粪可能代表新型隐球菌的实际生态位。由于格特隐球菌能在鸽粪上生长但不能进行有性繁殖，鸽粪对格特隐球菌来说代表一个基础但非实际的生态位。基于这些研究，我们推测一种祖先隐球菌菌株获得了在鸽粪中进行有性繁殖的能力，然后席卷全球。
