经济学人下载:微生物组学 病毒防护

Science and technology
科学技术

Microbiomics
微生物组学

A virus shield
病毒防护

Viruses help keep people disease-free
病毒能够帮助人类免遭疾病

THE story of the microbiome—the community of tiny organisms that coexist symbiotically with people and other animals—gets weirder every day.
微生物组指的就是能与人类和其他动物互依共存的微有机体群，关于生物体组的传言一天比一天古怪。

Until now that story, which has emerged over the past few years, has seemed one of friendly collaboration.
自其前些年出现至今，已经看作成一种友好互利的合作。

In exchange for a place to live, bacteria aid digestion and help regulate their host's metabolism.
只要它们寄住在寄主体内，细菌可以帮助寄主消化也可以调节寄主的新陈代谢。

The story's latest chapter, though, describes a different deal: between the animal host and viruses.
但是，关于生物体组的最新研究提出了一种不同的理论：在动物宿主和病毒的关系链之间还有细菌，

And in this deal, bacteria are the targets.
细菌是需要被消灭的。

Jeremy Barr of San Diego State University and his colleagues, who have just published their results in the Proceedings of the National Academy of Sciences, were intrigued by the high concentrations of viruses called bacteriophages in the mucus secreted by soft-tissue membranes ranging from the outer layers of sea anemones via the skins of fish to the mouths of people.
来自圣地亚哥分学的Barr及其同事，对叫噬菌体的一类病毒产生了浓厚的兴趣，它广泛存在于软组织膜分泌的粘液中，不管是海葵的外表面、鱼表面还是人类的口腔，他们将这一发现发表在《美国科学院院刊》上。

Such membranes are prime targets for pathogens, which is why so many people suffer from throat and lung infections, and upset guts.
这些软组织膜就是病原体的主要存在区域，这就是为什么许多人会嗓子发炎、肺部感染和得肠炎。

Bacteriophages parasitise bacteria, a process pictured schematically above.
噬菌体寄生在细菌内，寄生过程难以用一两句话说清楚。

Dr Barr wondered if they were actively working with their hosts to keep down the level of pathogenic bugs that might otherwise set up shop in the hosts' mucus membranes.
Barr博士觉得噬菌体或许可以帮助寄主降低致病菌的数量，防止病菌将在寄主的粘膜液中大量繁殖。

Regardless of which type of membrane they looked at, Dr Barr and his colleagues found about four times more phages per bacterium in the mucus than were in its immediate surroundings.
Barr博士和他的同事发现，无论在何种类型粘液中，每一个病菌对应噬菌体的数量要比粘液附近其他组织里的多四倍。

This suggested that phages are sticking specifically to mucus, and in an elegant series of experiments they found that this was true and that the thing on a phage which is doing the sticking is a “hypervariable” protein called Hoc.
这暗示噬菌体特定存在于粘液中，在一系列巧妙的实验之后，他们发现确实是这样并且发现噬菌体上存在一种称为Hoc的高变蛋白，正是由于这种蛋白质才会使噬菌体特定存在粘液中。

Hypervariable proteins come in thousands of slightly different versions.
细分的话，高变蛋白有好几千种。

The best studied is the mammalian antibody protein, immunoglobulin.
对这类蛋白研究最深入的要属哺乳动物抗体蛋白—免疫球蛋白。

Each of the versions of this protein that exist in every individual is capable of locking onto and neutralising a different invading pathogen, by interacting with different molecules on the pathogen's surface.
人体内有各种高变蛋白的噬菌体，噬菌体通过识别不同细菌的表面分子，做到一种噬菌体只侵噬一种入侵细菌。

In phages, Dr Barr discovered, the various versions of Hoc stick to the varied branched sugar molecules characteristic of mucus.
Barr博士发现不同的HOC蛋白与不同的粘液特征性多糖分子的支链相结合。

That helps the phages, because their bacterial prey also accumulate in mucus, which is thus a rich hunting ground.
因为细菌的侵染过程也是发生在粘液中，这就为噬菌体提供了大量的寄生宿主。

And it helps the animal host, be that host sea anemone, fish or human being, by stopping any particular bacterial species running out of control—for if a species does start to multiply, which is a normal precursor to infection, there will be more phages around to attack it and multiply in their turn, bringing the uppity bug rapidly under control.
这也帮助诸如海葵、鱼、人类一样的动物寄主防止某种细菌大量繁殖，因为细菌要感染宿主就必须先大量繁殖，这样周围会聚集更多的噬菌体来侵噬它们，并且噬菌体开始繁殖，迅速控制住这繁殖快速的细菌的数量。

The phages are thus acting as a backup immune system for their hosts, and one whose mode of operation has a surprising parallel with that of the more familiar antibody-based system.
对于寄主来说，噬菌体属于免疫系统的一部分，并且噬菌体的这种免疫系统与与它很相似的抗体免疫系统不相伯仲。