背景:微生物群的特征通常是共存的微生物物种和菌株的高度多样性,和微生物组组成通常在广泛的条件下保持稳定。然而,在固定条件下,微生物生态学符合排斥原则,在这种原则下,在同一生态位内竞争同一资源的两个种群不能共存,因为不太适合的种群不可避免地灭绝了。因此,微生物组多样性的长期持续存在需要一个解释。
结果:为了探索稳定微生物多样性的条件,我们开发了一个简单的数学模型,由两个竞争群体组成,可以通过水平基因转移(HGT)交换单个基因等位基因。我们发现,虽然在固定的环境中,有了公正的HGT,系统遵循排除原则,在一个振荡的环境中,在由繁殖率和HGT界定的相空间的大区域内,这两个群体共存。此外,根据参数组合,获得了所有三种主要的共生类型,即,纯粹的竞争,宿主-寄生虫关系,和互惠主义。在这些政权中,为协同提供的某些参数组合,也就是说,与固定环境中获胜种群的丰度相比,这两个种群的总丰度更高。
结论:这项建模研究的结果表明,在微生物群落中普遍存在的基本现象,即,环境变化和HGT,提供微生物多样性的稳定性和持久性,以及生态复杂性的出现。
BACKGROUND: Microbiomes are generally characterized by high diversity of coexisting microbial species and strains, and microbiome composition typically remains stable across a broad range of conditions. However, under fixed conditions, microbial ecology conforms with the exclusion principle under which two populations competing for the same resource within the same niche cannot coexist because the less fit population inevitably goes extinct. Therefore, the long-term persistence of microbiome diversity calls for an explanation.
RESULTS: To explore the conditions for stabilization of microbial diversity, we developed a simple mathematical model consisting of two competing populations that could exchange a single gene allele via horizontal gene transfer (HGT). We found that, although in a fixed environment, with unbiased HGT, the system obeyed the exclusion principle, in an oscillating environment, within large regions of the phase space bounded by the rates of reproduction and HGT, the two populations coexist. Moreover, depending on the parameter combination, all three major types of
symbiosis were obtained, namely, pure competition, host-parasite relationship, and mutualism. In each of these regimes, certain parameter combinations provided for synergy, that is, a greater total abundance of both populations compared to the abundance of the winning population in the fixed environment.
CONCLUSIONS: The results of this modeling study show that basic phenomena that are universal in microbial communities, namely, environmental variation and HGT, provide for stabilization and persistence of microbial diversity, and emergence of ecological complexity.