The Hidden Universe Within: An Introduction to the Gut Microbiome 隐秘宇宙：肠道微生物组导论

The Hidden Universe Within: An Introduction to the Gut Microbiome

隐秘宇宙：肠道微生物组导论

---

Chapter at a Glance | 本章概览

Every human being carries within their body a vast and teeming population of microscopic organisms—so numerous, so diverse, and so influential that scientists now regard them not as passive passengers but as an integral part of what it means to be human. This chapter answers the foundational questions: What is the gut microbiome? What is it made of? How did we come to understand it? And why does it matter for your health, your weight, your mood, and perhaps even your sense of self?

本章将回答以下基础问题：何为肠道微生物组？它由什么构成？我们如何逐步认知到它的存在？以及为什么它对你的健康、体重、情绪乃至自我认知都至关重要？

---

The Superorganism Concept: You Are Not Alone

超级有机体：你并非独行

When you look in a mirror, you see a single human being—a body, a face, a person. But from the perspective of biology, what stares back is something far more complex and far less singular. You are, in fact, a superorganism: a vast ecosystem inhabited by an extraordinary abundance of microscopic life.

当你照镜子时，你看到的是一个独立的人——一个躯体、一张面孔、一个生命个体。但从生物学的角度来看，你所看到的远不止这些。你其实是一个超级有机体：一个承载着海量微生物生命的复杂生态系统。

Consider the numbers. The human body is composed of approximately 37.2 trillion human cells, give or take a few trillion depending on which study you consult. For decades, this figure served as a biological constant, a reference point for medical textbooks. But then scientists began asking a different question: how many microbial cells inhabit the same body? The answer, once the counting methods became precise enough to yield reliable estimates, was startling. The human gut alone harbors approximately 38 trillion microbial cells. When you include the microorganisms residing on the skin, in the mouth, in the respiratory tract, and in the urogenital system, the total microbial population of a single individual comfortably exceeds the number of human cells in that same body.

让我们看看具体数据。人体大约由37.2万亿个人体细胞组成（不同研究略有差异）。几十年来，这个数字一直是生物学的基准参考。但当科学家们开始提出另一个问题时，答案令人震惊：一个人体内居住着多少微生物细胞？仅仅肠道本身就容纳了约38万亿个微生物细胞。如果将栖息于皮肤、口腔、呼吸系统和泌尿生殖系统中的微生物也计算在内，那么一个人的微生物总数将轻松超过其人体细胞的数量。

This was a profound shift in biological thinking. For most of the 20th century, the prevailing model of human biology treated the body as a closed system—a fortress defended by the immune system against invading pathogens. Microbes were either enemies to be eliminated or neutral entities too insignificant to warrant serious attention in the study of health and disease. The discovery that microbial cells outnumber human cells fundamentally challenged this paradigm. We are not fortified castles holding the line against microbial hordes. We are, instead, the biological equivalent of entire cities—complete with ecological niches, resource networks, competitive relationships, and cooperative alliances—populated by residents both microscopic and macroscopic, all sharing the same geography.

这是一个深刻的生物学思想转变。在20世纪的大部分时间里，人类生物学的主流模型将人体视为一个封闭系统——一座由免疫系统防守的堡垒，抵御入侵的病原体。微生物要么是需要被消灭的敌人，要么是无足轻重的中立存在，在健康与疾病研究中不配享有重要席位。但微生物细胞数量超过人体细胞这一发现从根本上颠覆了这一范式。我们不是固守防线对抗微生物大军的中世纪城堡；相反，我们更像是整座城市——拥有生态位、资源网络、竞争关系和协作联盟，栖居着微观的和宏观的居民，共同生活在同一片领地上。

The implications of this conceptual shift extend far beyond counting methodology. If we accept that the human body is a superorganism—a collaborative creation of human and microbial genomes—then the very definition of "human health" must be renegotiated. Health is no longer simply a matter of keeping human cells functioning correctly. It becomes a question of ecological balance, of maintaining the right relationships between host and symbiont, of ensuring that the microbial communities residing in and on our bodies are behaving in ways that support—or at least do not undermine—our wellbeing.

这一概念转变的意义远超计数方法本身。如果我们接受人体是超级有机体——人类基因组与微生物基因组协作创造的产物——那么"人体健康"的定义就必须重新审视。健康不再仅仅是维持人体细胞正常运作的问题，而成为生态平衡的问题：宿主与共生体之间需要维持恰当的关系，确保栖息于我们体内外的微生物群落以支持健康而非损害健康的方式运作。

The gut, in particular, functions as the capital city of this internal ecosystem. It houses the densest, most diverse, and most metabolically active microbial community in the human body. While the skin hosts roughly one million microorganisms per square centimeter, and the mouth contains hundreds of bacterial species, the colon—the final section of the large intestine—contains microbial densities that can exceed 100 billion organisms per gram of content. This extraordinary concentration of microbial life transforms the gut from a simple digestive tube into a biochemical factory of staggering complexity, capable of performing metabolic feats that the human genome alone could never accomplish.

肠道作为这个内在生态系统的"首都城市"，承载着人体内最密集、最多样化、代谢最活跃的微生物群落。皮肤每平方厘米约栖息100万个微生物，口腔含有数百种细菌，而结肠——大肠的最后一段——每克内容物的微生物密度可超过1000亿个。这种惊人的微生物生命密度，将肠道从一根简单的消化管道转变为一个极其复杂的生物化学工厂，能够完成仅凭人类基因组永远无法实现的代谢壮举。

> Key Insight 关键洞察 > > The human body contains approximately 38 trillion microbial cells, primarily concentrated in the gut, compared to roughly 37.2 trillion human cells. This numerical parity—along with the discovery that microbial genes outnumber human genes by approximately 150-fold—has fundamentally reshaped our understanding of what it means to be human. > > 人体包含约38万亿个微生物细胞（主要集中于肠道），而人体细胞约37.2万亿个。这一数量级的接近——加之微生物基因约为人类基因150倍这一发现——从根本上重塑了我们对"何为人类"的认知。

---

Microbial Census: Who Lives in Your Gut?

微生物普查：谁栖息在你的肠道？

Understanding the gut microbiome begins with understanding its residents. The term "gut microbiome" itself requires careful unpacking, because scientists typically distinguish between two related but distinct concepts. The microbiota refers to the actual community of living microorganisms inhabiting the gut—bacteria, viruses, fungi, archaea, and other less-studied entities. The microbiome refers to the collective genetic material of these organisms: the sum total of all their genes. When scientists talk about the "gut microbiome," they are often referring to both the microbial community and its collective genetic repertoire, and this distinction matters because it captures both who is there and what they are capable of doing.

理解肠道微生物组，首先要从了解其"居民"开始。"肠道微生物组"这个词本身需要仔细拆解，因为科学家通常区分两个相关但不同的概念。微生物群（microbiota）指的是栖息于肠道中的活体微生物群落——包括细菌、病毒、真菌、古菌以及其他研究较少的生命形式。微生物组（microbiome）则指的是这些生物的集体遗传物质：即所有微生物基因的总和。当科学家谈论"肠道微生物组"时，他们通常同时指代微生物群落本身及其集体基因库。这种区分之所以重要，是因为它同时涵盖了"谁在那里"以及"它们能做什么"。

Bacteria: The Dominant Inhabitants

细菌：主导居民

Bacteria are, by any measure, the most abundant and well-studied inhabitants of the gut. The adult human gut is estimated to contain between 1,000 and 1,500 distinct bacterial species, though an individual's personal microbiome typically numbers somewhere between 200 and 1,000 species. This variation reflects the remarkable individuality of the microbiome: no two people—not even identical twins raised in the same household—harbor exactly the same microbial community.

无论从哪个角度衡量，细菌都是肠道中数量最多、研究最深入的原住民。成年人肠道中估计有1,000至1,500种不同的细菌，但每个人的肠道微生物组通常只包含200至1,000种物种。这种差异反映了微生物组惊人的个体独特性：没有任何两个人——即使是同卵双胞胎在同一屋檐下长大——拥有完全相同的微生物群落。

The bacterial inhabitants of the gut belong to several major phyla, the broadest classification categories in bacterial taxonomy. The two dominant phyla in most healthy adults are Firmicutes and Bacteroidetes, which together typically account for 80 to 90 percent of all gut bacteria. Firmicutes is an extraordinarily diverse phylum that includes the genus *Lactobacillus*—familiar to many as the bacteria responsible for fermenting yogurt and sauerkraut—and *Clostridium*, a genus that contains both harmless commensals and dangerous pathogens. Bacteroidetes, as the name suggests, is dominated by the genus *Bacteroides*, highly efficient carbohydrate metabolizers that play a central role in extracting energy from dietary fiber.

肠道的细菌居民分属几个主要门——这是细菌分类学中最广泛的分类层级。大多数健康成年人中，两个优势门是厚壁菌门（Firmicutes）和拟杆菌门（Bacteroidetes），它们通常占所有肠道细菌的80%至90%。厚壁菌门是一个极其多样化的门，包括乳杆菌属（Lactobacillus）——很多人熟悉它是因为它是酸奶和酸菜发酵背后的功臣——以及梭菌属（Clostridium），该属包含无害的共生菌和危险的病原体。顾名思义，拟杆菌门由拟杆菌属（Bacteroides）主导，它们是高效