Nature等两篇文章发表细菌新知

　　

生物通报道：细菌是指一大类细胞核无核膜包裹，只存在称作拟核区(或拟核)的裸露DNA的原始单细胞生物，包括真细菌（eubacteria）和古生菌（archaea）两大类群。这种生物是自然界分布最广、个体数量最多的有机体，人类身体就是无数细菌的居所。近期两个不同的研究团队获得了这方面的重要研究进展，分别发表在Nature和Science杂志上。

第一篇文章是由来自新西兰梅西大学的研究人员完成，是Nature的封面文章，在这篇文章中，研究人员通过探讨一个“荧光假单孢菌”菌种的菌落在动态环境中的变化，从而发现细菌能形成了在不同菌落类型之间随机切换的能力。

在自然界，表现型之间的随机切换是生物在变幻无常的环境中求生存的常见现象。研究人员通过对暴露于一个与脊椎动物免疫系统等环境有相似性的波动体系中的“荧光假单孢菌”所做的一项研究，实时显示了这种行为何以能够发生。

Nature封面所示为一个“荧光假单孢菌”菌种的菌落，这个菌种已形成了在不同菌落类型之间随机切换的能力。这种策略使它们能够在一个不断变化、以对不同菌落有利的人工环境中存活。随机切换在实验室中的形成以及其中所涉及突变的识别，反映了动态环境是怎样推动这种随机切换行为之形成的。

另外一篇文章中，来自科罗拉多大学博尔德分校的研究人员对人的整个身体进行了多元微生物群落分析，绘制出人体细菌群落分布图，这将有利于揭示这些群落的变化将如何引起（或防止）疾病的发生。

研究人员研究人员对9名健康志愿者身上27个部位的细菌群落进行了长达3个月的深入观察分析。这些部位包括其中包括肠道、口腔、耳 朵、鼻子以及多达18 个区域的皮肤表面。在3个月内，研究人员分别对每名志愿者做了4次细菌采样。采样工作一般在志愿者洗澡1至2小时后进行。然后运用最新电脑技术及基因序列，研究人员绘制出了人体不同部位细菌分布的概况和轮廓。结果显示，不仅人与人之间菌群分布有别，同一个体不同部位菌群分布也不相同。此外，人体同一部位在不同时间菌群分布也有变化。

身体的部位对居留在那里的细菌群落的组成具有最大的影响，其影响远远大于时间的推移或个体之间的差异，研究人员发现，某些皮肤部位，如食指或膝盖的背侧常常比肠道或口腔能容留更为多元的微生物。他们的数据显示，我们身体的个体化的微生物随着时间的推移仍然保持着相对的稳定，而且它们展现了在我们身体各个位置生长的可预测的模式。

之后研究人员进行了进一步的实验，他们将身体某一部位的细菌群落移植到身体的另外一个部位，或从某人身上移植到另外一个人身上。结果发现，环境因素在油脂分泌多的皮肤部位比在皮肤干燥的部位对塑造微生物群落的影响力要更强。 例如，前臂的微生物在前额上的生长就不甚好，但前额的微生物在前臂上的生长则依然很好。

约有100万亿个细菌分布在人体内外。其中部分菌类在人体生理机能中作用突出，能够有效协助人体保持健康状态。例如有些菌类可以帮助人体构筑免疫系统；有些对促进食物消化不可或缺；还有的可以防止病原体引发潜在病变。理解人体菌群的分布变化差异对未来临床医学研究意义重大。

（生物通：万纹）

原文摘要：

Bacterial Community Variation in Human Body Habitats Across Space and Time

Elucidating the biogeography of bacterial communities on the human body is critical for establishing healthy baselines from which to detect differences associated with diseases. To obtain an integrated view of the spatial and temporal distribution of the human microbiota, we surveyed bacteria from up to 27 sites in 7 to 9 healthy adults on four occasions. We found that community composition was determined primarily by body habitat. Within habitats, interpersonal variability was high, while individuals exhibited minimal temporal variability. Several skin locations harbored more diverse communities than the gut and mouth, and skin locations differed in their community assembly patterns. These results indicate that our microbiota, although personalized, varies systematically across body habitats and time: Such trends may ultimately reveal how microbiome changes cause or prevent disease.
 

Experimental evolution of bet hedging

Bet hedging—stochastic switching between phenotypic states1, 2, 3—is a canonical example of an evolutionary adaptation that facilitates persistence in the face of fluctuating environmental conditions. Although bet hedging is found in organisms ranging from bacteria to humans4, 5, 6, 7, 8, 9, 10, direct evidence for an adaptive origin of this behaviour is lacking11. Here we report the de novo evolution of bet hedging in experimental bacterial populations. Bacteria were subjected to an environment that continually favoured new phenotypic states. Initially, our regime drove the successive evolution of novel phenotypes by mutation and selection; however, in two (of 12) replicates this trend was broken by the evolution of bet-hedging genotypes that persisted because of rapid stochastic phenotype switching. Genome re-sequencing of one of these switching types revealed nine mutations that distinguished it from the ancestor. The final mutation was both necessary and sufficient for rapid phenotype switching; nonetheless, the evolution of bet hedging was contingent upon earlier mutations that altered the relative fitness effect of the final mutation. These findings capture the adaptive evolution of bet hedging in the simplest of organisms, and suggest that risk-spreading strategies may have been among the earliest evolutionary solutions to life in fluctuating environments.