他她话题:现代医学 微生物造就人类(上)

POLITICAL revolutionaries turn the world upside down. Scientific ones more often turn it inside out. And that, almost literally, is happening to the idea of what, biologically speaking, a human being is.

世界在政治革命家手中上下颠倒，在科技革命者手中却常常里外颠倒。在字面上来看，这句话恰巧从生物学角度解释了：人类到底是什么。

The traditional view is that a human body is a collection of 10 trillion cells which are themselves the products of 23,000 genes. If the revolutionaries are correct, these numbers radically underestimate the truth. For in the nooks and crannies of every human being, and especially in his or her guts, dwells the microbiome: 100 trillion bacteria of several hundred species bearing 3m non-human genes. The biological Robespierres believe these should count, too; that humans are not single organisms, but superorganisms made up of lots of smaller organisms working together.

传统观点认为，人体是十万亿个细胞的集合体，这些细胞又是23000个基因表达后的生成物。如果生物革命者的观点正确，那这些数字就远远的低估了实际情况。因为在人体的各个部位，尤其是内脏寄居着微生物群落：来自几百个类型的上百万亿个细胞携带着300万个非人类基因。生物学家罗伯斯比尔认为：这些数字是有价值的，因为人体不是单一的有机个体，而是由成千上万个微小的有机体共同作用构成的超级个体。

It might sound perverse to claim bacterial cells and genes as part of the body, but the revolutionary case is a good one. For the bugs are neither parasites nor passengers. They are, rather, fully paid-up members of a community of which the human "host" is but a single (if dominating) member. This view is increasingly popular: the world's leading scientific journals, Nature and Science, have both reviewed it extensively in recent months. It is also important: it will help the science and practice of medicine.

要说细菌、细胞和基因是人体的一部分，可能令人无法接受，但这一革命性的结论确是有益的。这些小东西既非寄生生物，也非人体系统的过客，而是人体独立这个宿主环境内的忠实成员。这个观点越来越普及，全球先进的科学报刊《自然》和《科学》，用大篇幅对该观点进行评论，它的重要性在于能够帮助医学理论和实践的发展。

All in this together

齐聚一堂

The microbiome does many jobs in exchange for the raw materials and shelter its host provides. One is to feed people more than 10% of their daily calories. These are derived from plant carbohydrates that human enzymes are unable to break down. And not just plant carbohydrates. Mother's milk contains carbohydrates called glycans which human enzymes cannot digest, but bacterial ones can.

微生物群落通过许多工作向人体换取生存原材料和环境。有一种微生物向人体提供每月所需热量的10%，这些热量产生自一种人体酶无法分解的植物碳水化合物，其实不仅是植物糖类，人类母乳中包含的多糖也无法被人体自身的酶消化，细菌酶却可以。

This alone shows how closely host and microbiome have co-evolved over the years. But digestion is not the only nutritional service provided. The microbiome also makes vitamins, notably B2, B12 and folic acid. It is, moreover, capable of adjusting its output to its host's needs and diet. The microbiomes of babies make more folic acid than do those of adults. And microbiomes in vitamin-hungry places like Malawi and rural Venezuela turn out more of these chemicals than do those in the guts of North Americans.

这个例子只能说明人体和微生物群落是如何在几十年内协同作用产生进化的。但消化只是微生物为人体提供的多种营养服务之一，它们还能产生维生素，特别是B2、B12和叶酸（维生素B），此外它还能根据人体需要和膳食情况调节产量。婴儿体内的微生物可以产生比成人多的维B，维生素缺乏地区，如马拉维和委内瑞拉的农村，这些地方的人们内脏产生的维生素就要多于北美地区。

The microbiome also maintains the host's health by keeping hostile interlopers at bay. An alien bug that causes diarrhoea, for instance, is as much an enemy of the microbiome as of the host. Both have an interest in zapping it. And both contribute to the task. Host and microbiome, then, are allies. But there is more to it than that. For the latest research shows their physiologies are linked in ways which make the idea of a human superorganism more than just a rhetorical flourish.

微生物还通过抵御外界有毒物质入侵，帮助人体的健康。例如引起腹泻的细菌，是人体和体内微生物共同的敌人，两者都希望消灭它，这就需要"宿主"与微生物群联合才能完成任务。除此以外，近期研究还表明，人体与微生物在生理机能上也存在一定的联系，这让人体是超级个体的说法脱离了繁冗修辞的嫌疑。

These links are most visible when they go wrong. A disrupted microbiome has been associated with a lengthening list of problems: obesity and its opposite, malnutrition; diabetes (both type-1 and type-2); atherosclerosis and heart disease; multiple sclerosis; asthma and eczema; liver disease; numerous diseases of the intestines, including bowel cancer; and autism. The details are often obscure, but in some cases it looks as if bugs are making molecules that help regulate the activities of human cells. If these signals go wrong, disease is the consequence. This matters because it suggests doctors have been looking in the wrong place for explanations of these diseases. It also suggests a whole new avenue for treatment. If an upset microbiome causes illness, settling it down might effect a cure.

生理机能上的联系在它出现问题时体现得更加突出，微生物功能将产生许多问题：过度肥胖或消瘦；营养不良；1型和2型糖尿病；动脉硬化和心脏病；多发性硬化症；哮喘和湿疹；肝病；肠道内的多种疾病，包括肠道癌；孤独症。这些问题的细节不甚明了，但在一些病例中反应出，似乎微生物制造的分子可以帮助调节人体细胞功能。这一点很重要，因为它反映出医生在分析这些疾病时错误的切入点。同时也提出了出全新的治疗方法，如果是微生物功能紊乱引起疾病，那只需要解决这个问题就可能治愈。

Yogurt companies and health-food fanatics have been banging this drum for years. And in the case of at least one malady, irritable-bowel syndrome, they are right. So-called probiotics, a mixture of about half a dozen bacterial species found in yogurt, do act to calm this condition. But there is little evidence that consuming probiotics has the tonic effect on healthy people that certain adverts suggest.

酸奶制造商和营养品热衷者多年前就鼓吹这种说法。但至少在过敏性肠道综合症这个病症上，他们说对了，所谓的益生菌，主要存在于酸奶中，混合了大约六个菌种，可以缓解这一病症。但有些广告说益生菌对人体有滋补作用，目前暂无证据可以证实。

A handful of doctors are taking a more fundamental approach to another microbiome-related disease, infection with Clostridium difficile. This bacterium, which causes life-threatening distension of the gut in some people who have been treated with antibiotics and thus had their microbiomes disrupted, is a bane of hospitals. It kills 14,000 people a year in America alone. But recent experiments have shown it can be eliminated by introducing, as an enema, the faeces of a healthy individual. "Stool transplants" are a pretty crude approach, to be sure, but the crucial point is that microbes are much easier to manipulate than human cells. For all the talk of superorganisms (and despite the yuck factor of what is being moved from one body to another), transplanting a microbiome is far easier than transplanting a heart or a kidney.

一小部分医生采取更为基本的方式治疗另外一与微生物有关的疾病：梭状芽胞杆菌感染。一些病患曾接受抗生素治疗。导致体内微生物群落紊乱。梭状芽胞杆菌可以引起致命的肠道扩张，这种病向来是让医院极其苦恼的，仅在美国，每年死于该疾病的就有14000人。但近期有实验结果表明，可将一个健康人体的粪便，用灌肠剂的方法引入体内消除这类芽胞杆菌。粪便移植的确是种残忍的手段，不可否认，但关键在于处理微生物要比人体细胞简便得多。尽管关于超级有机体众说纷纭，尽管在人体间转移的东西很恶心，移植微生物的简易性远不是心脏或肾脏移植可比。