北京时间11月13日消息，科学家已经知道我们肚脐里最常见的细菌种类，但不同人的肚脐里细菌种类是否相同？是什么在影响细菌种类的变化？这些都是北卡罗来纳州立大学的罗布•邓恩博士想要解决的问题。作为“肚脐生物多样性”项目的负责人，以下就是他最近的研究成果。
你想过这里居住着什么生物吗？
研究发现的大部分微生物种类都属于微球菌属（Micrococcus），为放线菌的种类。
研究者用棉签从66位参与者的肚脐上擦拭取下样品，然后通过高通量基因测序确定每个样品里的微生物种类(或称种系型，phylotype)，以及这些微生物的出现频率。此项研究中，只要16s rDNA(脱氧核糖核酸重组体)序列与其他种类的差异在3%以上，就可以确定为新的生物体。从这个意义上说，16s rDNA就像是微生物的基因指纹。
研究者发现了成千上万的微生物，但只有一小部分是在人群里常见，绝大多数种类都只出现了一两次。具体来说，研究中一共发现了2368种微生物，包括首次发现的3种古菌。然而，只有8种细菌在70%以上的实验者身上都有发现。这8种细菌也是数量最丰富的种类，几乎占了样品细菌总量的一半。
“最常见，而且数量最大的种类来自于一个相对少数的进化路线，表明它们已经进化出了适应在人类皮肤上生活的特征，”邓恩说，“然而，我们依旧不知道这些种类是否会在特定的人身上出现。我们分析了性别、年龄、种族以及其他许多因素，但都不能预测出某个人身上会出现什么细菌。”
研究者们之所以提出“肚脐生物多样性”项目，很大一部分原因是，近几年来对人体体表微生物的研究已经发现，这些微生物是人体对抗疾病的第一道防线。“我们知道，没有了这些微生物，我们的免疫系统就不能正常工作，”邓恩说，“事实上，这些微生物应该具有特定的种类组成，即形成某种微生物生态系统，以利于人体免疫系统正常运作。这项工作将有助于我们了解哪些种类在这些生态系统中最为重要。”
至于为什么选择从肚脐采样，研究者给出了两个答案。首先，这是人身体上一个受外界影响很小的代表部位；其次，研究者希望能够让公众参与到科学研究中来。“研究肚脐一听起来就很搞笑，”邓恩说，“这会抓住人们的眼球。”
研究人员发现，实验者的肚脐中平均有67种不同的细菌，而且其中很多细菌的发现相当意外，有些基本上只在海洋环境和外国土地上才能发现。有关这一研究的论文在线发表在《PLOS-ONE》上。
A Jungle in There: Bacteria in Belly Buttons are Highly Diverse, but Predictable
Jiri Hulcr, Andrew M. Latimer, Jessica B. Henley, Nina R. Rountree, Noah Fierer, Andrea Lucky, Margaret D. Lowman, Robert R. Dunn
The belly button is one of the habitats closest to us, and yet it remains relatively unexplored. We analyzed bacteria and arachaea from the belly buttons of humans from two different populations sampled within a nation-wide citizen science project. We examined bacterial and archaeal phylotypes present and their diversity using multiplex pyrosequencing of 16S rDNA libraries. We then tested the oligarchy hypothesis borrowed from tropical macroecology, namely that the frequency of phylotypes in one sample of humans predicts its frequency in another independent sample. We also tested the predictions that frequent phylotypes (the oligarchs) tend to be common when present, and tend to be more phylogenetically clustered than rare phylotypes. Once rarefied to four hundred reads per sample, bacterial communities from belly buttons proved to be at least as diverse as communities known from other skin studies (on average 67 bacterial phylotypes per belly button). However, the belly button communities were strongly dominated by a few taxa: only 6 phylotypes occurred on >80% humans. While these frequent bacterial phylotypes (the archaea were all rare) are a tiny part of the total diversity of bacteria in human navels (<0.3% of phylotypes), they constitute a major portion of individual reads (~1/3), and are predictable among independent samples of humans, in terms of both the occurrence and evolutionary relatedness (more closely related than randomly drawn equal sets of phylotypes). Thus, the hypothesis that “oligarchs” dominate diverse assemblages appears to be supported by human-associated bacteria. Although it remains difficult to predict which species of bacteria might be found on a particular human, predicting which species are most frequent (or rare) seems more straightforward, at least for those species living in belly buttons.
文献链接：A Jungle in There: Bacteria in Belly Buttons are Highly Diverse, but Predictable
