欢迎来到微观世界 / Welcome to the Microbial World

想象一下，此刻你正悠闲地坐在窗边，阳光透过玻璃洒在手上，感受着温暖与惬意。你或许会想到这束阳光要花八分钟才能从太阳抵达地球，想到光年之外的星辰，想到宇宙的浩瀚无垠。但你是否曾想过，就在这同一时刻，在你看不见的皮肤表面，在你呼吸的每一口空气里，在你肠道蜿蜒数米的深处，正有无数微小得超乎想象的生命在忙碌着、繁殖着、老去着？它们比你已知的任何动植物都要古老，比人类文明存在的时间要漫长万亿倍。它们就是微生物——这个星球上最早的居民，也是最容易被我们忽视的存在。

Imagine for a moment that you're sitting leisurely by a window, sunlight streaming through the glass onto your hands, feeling its warmth. You might think about how this sunlight took eight minutes to travel from the sun to Earth, about the stars beyond the light-years, about the vastness of the universe. But have you ever considered that at this very moment, on the invisible surface of your skin, in every breath of air you inhale, deep within the winding meters of your intestines, countless life forms so tiny they defy imagination are busy working, reproducing, growing old, and passing away? They are older than any known plants or animals, more ancient than human civilization by trillions of years. They are microorganisms—the earliest residents of this planet and the existence we most easily overlook.

你可能会说：这和我有什么关系？微生物不是会让人生病的罪魁祸首吗？感冒、流感、肺炎、食物中毒……这些词汇背后，似乎都站着那些看不见的细菌和病毒。这个想法如此根深蒂固，以至于我们从小就被教导要"讲卫生"——洗手、消毒、远离脏东西。超市货架上摆满了抗菌肥皂、消毒湿巾、杀菌喷雾，我们似乎生活在一个与微生物势不两立的世界里。

You might say: What does this have to do with me? Aren't microorganisms the culprits that make us sick? Colds, flu, pneumonia, food poisoning... behind these words, it seems that invisible bacteria and viruses are standing guard. This idea is so deeply rooted that we were taught from childhood to be "hygienic"—wash hands, disinfect, stay away from dirty things. Supermarket shelves are filled with antibacterial soaps, disinfectant wipes, and sterilization sprays. We seem to live in a world at war with microorganisms.

然而，当你读完这本书之后，你可能会对这个"常识"产生深深的怀疑。因为事实的真相，远比我们以为的要复杂得多、有趣得多。

However, after you finish this book, you may have deep doubts about this "common sense." Because the truth is far more complex and interesting than we ever imagined.

重新认识微生物：比你想象的更神奇

Rediscovering Microorganisms: More Miraculous Than You Think

让我们先来回答一个最基本的问题：什么是微生物？"Microbe"这个词来自希腊语，"mikros"意为"小"，"bios"意为"生命"。顾名思义，微生物就是"微小的生命"，但这个"小"字，却是如此极端地小，以至于我们的大脑很难真正理解它的含义。

Let's start by answering the most fundamental question: What are microorganisms? The word "microbe" comes from Greek, "mikros" meaning "small" and "bios" meaning "life." As the name suggests, microorganisms are "tiny life forms," but this "tiny" is so extremely small that our brains can hardly truly grasp its meaning.

如果把一个典型的细菌放在数字"1"旁边，它大概只相当于印刷字体中句号的千分之一。这意味着，一滴普通自来水中含有的细菌数量，可能比整个撒哈拉沙漠里的沙粒还要多。想象一下那个画面：一滴水的容量里，藏着一个"沙漠"的生机。

If we place a typical bacterium next to the number "1," it would be about one-thousandth the size of a period in printed text. This means the number of bacteria in a single drop of ordinary tap water might exceed the total number of sand grains in the entire Sahara Desert. Just imagine that scene: within a droplet of water, an entire "desert" of life is hidden.

微生物的世界是一个超级微观的世界，其尺寸以微米（μm）为单位计算。一微米等于千分之一毫米。而人体的细胞通常在10到100微米之间，最大的细胞——卵细胞——直径可达100微米以上。至于细菌，大多数宽度在0.5到5微米之间，长度在1到10微米之间。病毒则更为渺小，大多数病毒的直径仅有20到300纳米，一纳米等于千分之一微米。

The microbial world is a super-microscopic world, measured in micrometers (μm). One micrometer equals one-thousandth of a millimeter. Human cells typically range from 10 to 100 micrometers, with the largest cell—the egg cell—reaching over 100 micrometers in diameter. As for bacteria, most are between 0.5 and 5 micrometers wide and 1 to 10 micrometers long. Viruses are even smaller, most having diameters of only 20 to 300 nanometers, with one nanometer equaling one-thousandth of a micrometer.

在微生物的王国里，存在着多种多样的成员。其中最著名的几大门派包括：

Within the kingdom of microorganisms, there are various diverse members. The most famous factions include:

细菌（Bacteria）：最常见的微生物类型，它们是单细胞生物，没有细胞核，属于原核生物。细菌的形状多种多样——有的像小球（球菌），有的像小棒（杆菌），有的像螺旋（螺旋菌），还有的像弯弯的月牙（弧菌）。你的口腔里、肠道里、皮肤上，到处都有细菌的身影。

Bacteria (Bacteria): The most common type of microorganism, they are single-celled organisms without a cell nucleus, classified as prokaryotes. Bacteria come in many shapes—some like tiny balls (cocci), some like small rods (bacilli), some like spirals (spirilla), and some like curved crescents (vibrios). Bacteria are found everywhere—on your mouth, intestines, and skin.

古细菌（Archaea）：曾经长期被误认为和细菌是一类，直到20世纪70年代才被确认为一个独立的生命分支。它们同样没有细胞核，但基因和生化特性与细菌截然不同。古细菌常常生活在极端环境中——滚烫的温泉、强酸性的湖泊、高盐度的死海——因此被称为"极端微生物"。不过，最新的研究也发现，古细菌在人体内也有分布。

Archaea (Archaea): Once long mistaken as being of the same type as bacteria, they were only recognized as an independent branch of life in the 1970s. They also lack a cell nucleus, but their genetic and biochemical characteristics are completely different from bacteria. Archaea often live in extreme environments—boiling hot springs, highly acidic lakes, and highly saline bodies of water like the Dead Sea—earning them the nickname "extremophiles." However, the latest research has also found Archaea present within the human body.

真菌（Fungi）：与细菌和古细菌不同，真菌是真核生物，拥有完整的细胞核和细胞器。厨房里发霉的面包、酿酒的酵母、致幻的蘑菇，都是真菌家族的一员。我们体内的真菌群落规模比细菌小得多，但同样扮演着重要角色。

Fungi (Fungi): Unlike bacteria and archaea, fungi are eukaryotes with complete cell nuclei and organelles. Moldy bread in the kitchen, yeast used in winemaking, and hallucinogenic mushrooms are all members of the fungi family. The fungal community in our bodies is much smaller than bacteria, but equally important.

病毒（Viruses）：这是一个特殊的存在。严格来说，病毒并不被认为是"活的"，因为它们没有细胞结构，不能独立进行新陈代谢，必须入侵活细胞才能复制自己。病毒由DNA或RNA遗传物质和蛋白质外壳组成，尺寸比细菌小得多。感冒病毒、流感病毒、新冠病毒，都是这个家族的"名人"。但别急着给病毒贴上"坏蛋"的标签，后面的内容会告诉你，事情远比这复杂。

Viruses (Viruses): This is a special existence. Strictly speaking, viruses are not considered "alive" because they have no cellular structure, cannot independently carry out metabolism, and must invade living cells to replicate themselves. Viruses consist of DNA or RNA genetic material and a protein shell, and are much smaller than bacteria. Cold viruses, flu viruses, and COVID-19 viruses are all "celebrities" of this family. But don't rush to label viruses as "bad guys"—the following content will show you that things are far more complex than this.

原生动物（Protists）：这是一类单细胞真核生物，包括阿米巴原虫、疟原虫等。有些原生动物是人体内的寄生虫，可能导致疾病；但也有些是肠道中的有益居民。

Protists (Protists): These are single-celled eukaryotes, including amoebas and malaria parasites. Some protists are human parasites that can cause disease; but others are beneficial residents in the intestines.

还有一群容易被忽视的微小居民：微型真核生物（microeukaryotes），包括某些藻类、原生动物和真菌。它们在人体内的角色正在被逐渐揭示，虽然目前了解还不多，但可以确定的是，它们同样是这个复杂生态系统的重要组成部分。

There's also a group of easily overlooked tiny residents: microeukaryotes, including certain algae, protozoa, and fungi. Their role in the human body is being gradually revealed. Although our understanding is still limited, we can be certain they are equally important components of this complex ecosystem.

说了这么多，你可能会想：好吧，我承认微生物很小、很多、很复杂。但它们真的对我有那么重要吗？答案是：是的，而且比你想象的重要得多。

After all this, you might think: Okay, I admit microorganisms are small, numerous, and complex. But are they really that important to me? The answer is: Yes, and more than you could ever imagine.

你不只是"你"：人体微生物组的发现之旅

You're Not Just "You": The Journey of Discovering the Human Microbiome

2003年，人类基因组计划宣告完成。科学家们耗时十三年、耗费数十亿美元，终于绘制出了人类基因组的完整图谱。这本"人类生命说明书"包含了大约两万到两万五千个基因，负责编码人体的各种蛋白质和调控生命活动。这是一个了不起的成就，理所当然地成为了全球头条新闻。

In 2003, the Human Genome Project was declared complete. Scientists spent thirteen years and billions of dollars finally drawing the complete map of the human genome. This "instruction manual for human life" contains approximately 20,000 to 25,000 genes responsible for encoding various proteins in the human body and regulating life activities. This was a remarkable achievement and naturally became global headline news.

然而，就在这个历史性时刻，一个不起眼的念头在少数科学家的脑海中萌芽：如果我们把注意力从人类基因转向人体内那些共生微生物的基因，会发现什么呢？

However, at this historic moment, an inconspicuous idea sprouted in the minds of a few scientists: What if we shifted our attention from human genes to