Division Biological Sciences, University of Montana, Missoula, Montana, USA.
School of Biology, Georgia Institute of Technology, Atlanta, Georgia, USA.
Appl Environ Microbiol. 2020 Apr 1;86(8). doi: 10.1128/AEM.00051-20.
The productivity of a biological community often correlates with its diversity. In the microbial world this phenomenon can sometimes be explained by positive, density-dependent interactions such as cross-feeding and syntrophy. These metabolic interactions help account for the astonishing variety of microbial life and drive many of the biogeochemical cycles without which life as we know it could not exist. While it is difficult to recapitulate experimentally how these interactions evolved among multiple taxa, we can explore in the laboratory how they arise within one. These experiments provide insight into how different bacterial ecotypes evolve and from these, possibly new "species." We have previously shown that in a simple, constant environment a single clone of can give rise to a consortium of genetically and phenotypically differentiated strains, in effect, a set of ecotypes, that coexist by cross-feeding. We marked these different ecotypes and their shared ancestor by integrating fluorescent protein into their genomes and then used flow cytometry to show that each evolved strain is more fit than the shared ancestor, that pairs of evolved strains are fitter still, and that the entire consortium is the fittest of all. We further demonstrate that the rank order of fitness values agrees with estimates of yield, indicating that an experimentally evolved consortium more efficiently converts primary and secondary resources to offspring than its ancestor or any member acting in isolation. Polymicrobial consortia occur in both environmental and clinical settings. In many cases, diversity and productivity correlate in these consortia, especially when sustained by positive, density-dependent interactions. However, the evolutionary history of such entities is typically obscure, making it difficult to establish the relative fitness of consortium partners and to use those data to illuminate the diversity-productivity relationship. Here, we dissect an consortium that evolved under continuous glucose limitation in the laboratory from a single common ancestor. We show that a partnership consisting of cross-feeding ecotypes is better able to secure primary and secondary resources and to convert those resources to offspring than the ancestral clone. Such interactions may be a prelude to a special form of syntrophy and are likely determinants of microbial community structure in nature, including those having clinical significance such as chronic infections.
生物群落的生产力通常与其多样性相关。在微生物世界中，这种现象有时可以通过正密度依赖相互作用来解释，例如交叉喂养和共生。这些代谢相互作用有助于解释微生物生命的惊人多样性，并驱动许多生物地球化学循环，如果没有这些循环，我们所知的生命就不可能存在。虽然很难在实验中重现这些相互作用在多个分类群中是如何进化的，但我们可以在实验室中探索它们在一个分类群中是如何产生的。这些实验为我们提供了深入了解不同细菌生态型如何进化的视角，并从中可能产生新的“物种”。我们之前已经表明，在一个简单、恒定的环境中，单个 的克隆可以产生一组遗传和表型上分化的菌株，实际上是一组生态型，通过交叉喂养而共存。我们通过将荧光蛋白整合到它们的基因组中来标记这些不同的生态型及其共享祖先，然后使用流式细胞术表明，每个进化的菌株都比共享祖先更适应，进化的菌株对更适应，整个联合体是所有中最适应的。我们进一步证明，适应度值的秩与产量估计值一致，表明实验进化的联合体比其祖先或任何单独作用的成员更有效地将初级和次级资源转化为后代。多微生物联合体存在于环境和临床环境中。在许多情况下，这些联合体中的多样性和生产力相关，尤其是在受到正密度依赖相互作用的支持时。然而，这些实体的进化历史通常是模糊的，使得难以确定联合体伙伴的相对适应度，并利用这些数据阐明多样性-生产力关系。在这里，我们从一个单一的共同祖先中分离出一个在实验室中连续葡萄糖限制下进化的 联合体。我们表明，由交叉喂养生态型组成的伙伴关系能够更好地获取初级和次级资源，并将这些资源转化为后代，而不是祖先克隆。这种相互作用可能是一种特殊形式的共生的前奏，并且很可能是自然微生物群落结构的决定因素，包括那些具有临床意义的，如慢性感染。
