A New Way That a Cow’s Inner World Shapes Earth’s Atmosphere
Ada Zejun Shen/ Quanta Magazine
沉泽君/广达杂志
W ithin every cow is a thriving ecosystem.
每头牛体内都有一个欣欣向荣的生态系统。
Churning deep in its intestines, a massive fermentation chamber known as the rumen hosts a robust microbiome that can consume up to 100 pounds of feed daily.
在它的肠道深处，有一个被称为瘤胃的巨大发酵室，里面有一个强大的微生物群，每天可以消耗多达 100 磅的饲料。
Inside this gut pouch, tens of millions of bacteria scavenge for scraps of fiber, starch, and other nutrients, and break down cellulose and proteins.
在这个肠袋内，数以千万计的细菌清除纤维、淀粉和其他营养物质的碎片，并分解纤维素和蛋白质。
They get a hand from microbial fungi, whose enzymes demolish stiff cell walls, and all are ruled by ciliates: large, predatory microbes that gorge themselves on bacteria.
它们得到了微生物真菌的帮助，微生物真菌的酶可以破坏坚硬的细胞壁，并且所有这些都由纤毛虫统治：纤毛虫是一种以细菌为食的大型掠食性微生物。
This complex food web transforms a bounty of compounds to fuel the cow’s metabolism.
这种复杂的食物网转化了大量的化合物来促进奶牛的新陈代谢。
Little goes to waste: Even hydrogen gas and carbon dioxide, the byproducts of fermentation, are scavenged by opportunists in this dark, warm, oxygen-free world.
几乎没有浪费：在这个黑暗、温暖、无氧的世界里，甚至发酵副产品氢气和二氧化碳也会被机会主义者清除。
Those opportunists are rumen microbes called methanogens, and their waste product is methane, a notoriously powerful heat-trapping greenhouse gas .
这些机会主义者是被称为产甲烷菌的瘤胃微生物，它们的废物是甲烷，这是一种众所周知的强大的吸热温室气体。
In this way, the inner world of a cow has global significance.
这样，牛的内心世界就具有了全球意义。
Ruminant livestock, including cows, goats, and sheep, have burped out about a third of all methane gas in the atmosphere.
包括牛、山羊和绵羊在内的反刍牲畜打嗝排出的甲烷气体占大气中约三分之一。
All told, when combined with more methane from landfills and fossil fuels, the gas is responsible for around 30% of the rise in global temperatures over the past 150 years.
总而言之，与垃圾填埋场和化石燃料产生的更多甲烷相结合，过去 150 年全球气温上升的 30% 左右是由这些气体造成的。
But it has a weak spot: It decays more quickly than carbon dioxide.
但它有一个弱点：它比二氧化碳分解得更快。
That’s why cow gas has attracted interest from researchers across the globe.
这就是为什么牛气引起了全球研究人员的兴趣。
They are looking into livestock’s specialized stomachs to identify the biological mechanisms that produce methane, which could be targeted to slow global warming within our lifetimes.
他们正在研究牲畜的特殊胃，以确定产生甲烷的生物机制，这可能是在我们有生之年减缓全球变暖的目标。
A recent study published in Science has revealed a clue wrapped in a membrane.
最近发表在《科学》杂志上的一项研究揭示了一条包裹在薄膜中的线索。
Amid new genome sequences for 450 ciliates — the rumen’s apex predators — researchers followed a trail that led them to an organelle, new to science, that is essential to the biochemical process of rebuilding atoms into compounds that are heating the planet.
在 450 种纤毛虫（瘤胃顶端捕食者）的新基因组序列中，研究人员追踪了一条线索，发现了一种新的科学细胞器，它对于将原子重建为加热地球的化合物的生化过程至关重要。
They named it the “hydrogenobody” because it produces hydrogen gas, which methanogens then turn into methane.
他们将其命名为“氢体”，因为它产生氢气，然后产甲烷菌将其转化为甲烷。
The findings offer new ideas for managing this pervasive source of warming, said Juan Tricarico , who researches enteric, or intestinal, methane at Dairy Management Inc ., a nonprofit trade association for dairy farmers, and was not involved in the recent study.
胡安·特里卡里科（Juan Tricarico）表示，这些发现为管理这种普遍的变暖源提供了新思路。他在乳业管理公司（一家面向奶农的非营利性贸易协会）研究肠道甲烷，并没有参与最近的这项研究。
“Just targeting the methanogens is probably not enough.”
“仅仅针对产甲烷菌可能还不够。”
Understanding how microscopic organisms lead to changes at a planetary scale will require further disentangling of the rumen’s microbial food web and the specific mechanisms by which they produce methane, he added.
他补充说，了解微生物如何导致全球范围内的变化需要进一步解开瘤胃微生物食物网及其产生甲烷的具体机制。
“We want to understand the environment under which these microbes thrive.”
“我们想了解这些微生物繁衍生息的环境。”
Even though ciliates have been studied for over a century, their role in the cow-gut ecosystem has been neglected compared to the far more numerous bacteria.
尽管纤毛虫的研究已经有一个多世纪了，但与数量多得多的细菌相比，它们在牛肠道生态系统中的作用却被忽视了。
Microbiologists know they are the largest single-celled organisms in the rumen.
微生物学家知道它们是瘤胃中最大的单细胞生物。
Under a microscope, their hairlike cilia sweep the area outside the cell like wispy brooms, pulling bacteria into their mouths and pushing them around.
在显微镜下，它们的毛发状纤毛像纤细的扫帚一样扫过细胞外的区域，将细菌拉进嘴里并推动它们四处移动。
Powering all those cilia takes a lot of energy, and making that energy releases hydrogen gas, which is then consumed by bacteria and archaea, including methanogens.
为所有这些纤毛提供动力需要大量能量，而这些能量会释放氢气，然后被细菌和古细菌（包括产甲烷菌）消耗。
“The whole rumen system is highly evolved, it’s highly synergistic, it’s highly symbiotic, and it’s evolved to consume all of that hydrogen,” said Rod Mackie , a rumen microbiologist at University of Illinois, Urbana-Champaign, who was not involved in the new study.
“整个瘤胃系统是高度进化的，它是高度协同的，它是高度共生的，它的进化是为了消耗所有的氢，”伊利诺伊大学厄巴纳-香槟分校的瘤胃微生物学家罗德·麦基（Rod Mackie）说，他没有参与这项新研究。
“And they [methanogenic archaea] do it by shunting that into mainly methanogenesis.”
“他们[产甲烷古菌]通过将其分流到主要产甲烷作用来做到这一点。”
To better understand the specific roles of rumen ciliates in methane emissions, microbiologists have turned to genomics.
为了更好地了解瘤胃纤毛虫在甲烷排放中的具体作用，微生物学家转向基因组学。
In 2021, Zhongtang Yu, a rumen microbiologist at Ohio State University, sequenced the very first rumen ciliate genome from a species called Entodinium caudatum ; its genus includes roughly 90% of all ciliates in livestock rumens.
2021年，俄亥俄州立大学瘤胃微生物学家Zhongtang Yu对一种名为Entodinium caudatum的物种的第一个瘤胃纤毛虫基因组进行了测序；该属包括家畜瘤胃中大约 90% 的纤毛虫。
A few years later, Yu assisted another team in sequencing the genomes of 52 additional rumen ciliates — a good start, but far from representative of the cow microbiome’s ciliate diversity.
几年后，Yu 协助另一个团队对另外 52 种瘤胃纤毛虫的基因组进行了测序——这是一个良好的开始，但远不能代表牛微生物组纤毛虫的多样性。
So when the 2026 study in Science reported 450 new ciliate genome sequences, jaws dropped across the rumen microbiome community.
因此，当《科学》杂志 2026 年的研究报道了 450 个新的纤毛虫基因组序列时，整个瘤胃微生物群落都惊呆了。
(The study’s authors, most of whom are based at the Chinese Academy of Sciences or Nanjing Agricultural University, did not respond to interview requests from Quanta Magazine .) The genomes have been added to a database where any researcher can access and study the ciliate sequences.
（该研究的作者大部分来自中国科学院或南京农业大学，他们没有回应广达杂志的采访请求。）基因组已添加到数据库中，任何研究人员都可以访问和研究纤毛虫序列。
The paper’s authors got a head start by searching the genomes for gene sequences of methane-making enzymes — including hydrogenases, the enzymes that catalyze the formation of hydrogen gas.
该论文的作者通过在基因组中搜索产生甲烷的酶（包括氢化酶，催化氢气形成的酶）的基因序列，取得了先机。
They found that some of the ciliates’ hydrogenases were different from all known versions of the enzymes found across life.
他们发现，一些纤毛虫的氢化酶与生命中发现的所有已知酶不同。
Experiments to locate these unusual enzymes found them in an unusual place, too: right at the edge of the cell membrane.
定位这些不寻常酶的实验也发现它们位于一个不寻常的地方：就在细胞膜的边缘。
Electron microscope images of several prominent ciliate species revealed why.
几种著名纤毛虫物种的电子显微镜图像揭示了原因。
Lining the outer cell membrane, at the base of the cilia, were simple structures, each encircled by a single membrane.
位于纤毛底部的外细胞膜上有简单的结构，每个结构都被单层膜包围。
Inside was hydrogenase.
里面是氢化酶。
The ciliates seemed to have organelles, the newly described hydrogenobodies, specially placed to provide energy to cilia.
纤毛虫似乎有细胞器，即新描述的氢体，专门为纤毛提供能量。
At its most basic, an organelle is a membrane-bound structure with a specialized function that is “recognized as having a different molecular signature than anything else in the cell,” said Aaron Turkewitz , a cell biologist and emeritus professor at the University of Chicago who was not involved in the research.
从最基本的角度来看，细胞器是一种具有特殊功能的膜结合结构，“被认为具有与细胞中其他任何东西不同的分子特征”，未参与这项研究的芝加哥大学细胞生物学家、名誉教授 Aaron Turkewitz 说。
The hydrogenobody, like the nucleus and mitochondria, fits this description.
氢体，如细胞核和线粒体，符合这一描述。
“Finding a new organelle is pretty exciting,” he said.
“找到新的细胞器非常令人兴奋，”他说。
When the study’s authors looked closer, they noticed that some ciliates had more hydrogenobodies than others.
当该研究的作者仔细观察时，他们注意到一些纤毛虫比其他纤毛虫具有更多的氢体。
Isotrichs, one prominent type, are “huge,” Tricarico said, at least by microbial standards.
特里卡里科说，等绒毛虫是一种重要的类型，至少从微生物标准来看是“巨大的”。
They are covered in cilia that resemble fur and have far more hydrogenobodies on their cell membrane to fuel those cilia.
它们覆盖着类似于毛皮的纤毛，并且细胞膜上有更多的氢体来为这些纤毛提供燃料。
Entodinomorphs, on the other hand, are smaller, with cilia and hydrogenobodies only in certain areas.
另一方面，内甲型动物较小，仅在某些区域具有纤毛和氢抗体。
Each type of ciliate occupies a different niche in the rumen, the same way that lions and cheetahs have different roles as predators on the savanna, Tricarico said.
特里卡里科说，每种纤毛虫在瘤胃中占据不同的生态位，就像狮子和猎豹作为稀树草原上的掠食者扮演不同的角色一样。
Within the organelle, the hydrogenase enzyme isn’t just interesting for its role in hydrogen production; it also uses up oxygen.
在细胞器内，氢化酶不仅因其在氢气生产中的作用而令人感兴趣，而且还因其在氢气生产中的作用而令人感兴趣。它还消耗氧气。
This action supports methanogens, too, since they are inhibited by oxygen .
这种作用也支持产甲烷菌，因为它们受到氧气的抑制。
The hydrogenobodies therefore help keep the dark cave of the rumen oxygen-free enough for methanogens to thrive, in addition to providing them with a raw material.
因此，除了为产甲烷菌提供原材料外，氢体还有助于保持瘤胃黑暗洞穴的无氧状态，足以让产甲烷菌繁衍生息。
The whole rumen system is highly evolved, it’s highly synergistic, it’s highly symbiotic.
整个瘤胃系统高度进化，高度协同，高度共生。
Rod Mackie, University of Illinois, Urbana-Champaign
罗德·麦基，伊利诺伊大学厄巴纳-香槟分校
It seemed plausible that these hydrogen-producing organelles were part of the methane puzzle, but to be certain, the researchers needed to know whether they noticeably affected methane production.
这些产氢细胞器似乎是甲烷难题的一部分，但为了确定这一点，研究人员需要知道它们是否明显影响甲烷的产生。
To test this, they measured methane emissions from 100 dairy cows using a gas-measuring device called a head box, which is exactly what it sounds like: a box that surrounds a cow’s head to measure its methane burps.
为了测试这一点，他们使用一种称为头盒的气体测量装置测量了 100 头奶牛的甲烷排放量，顾名思义，这是一个围绕牛头的盒子，用于测量其甲烷打嗝情况。
Then they analyzed the composition of isotrich and entodinomorph ciliates within the cows’ rumens.
然后他们分析了牛瘤胃内等丝纤毛虫和内体纤毛虫的组成。
They found that cows with more isotrichs — and therefore more hydrogenobodies — had much higher methane readings than those whose microbiomes were dominated by entodinomorphs.
他们发现，拥有更多等丝菌的奶牛——因此也有更多的氢体——比那些微生物组以内体形态为主的奶牛的甲烷读数要高得多。
Scientists have long suspected that ciliates are associated with methane emissions, Yu said.
余说，科学家们长期以来一直怀疑纤毛虫与甲烷排放有关。
The new study confirms the suspicion at a mechanistic level, presenting new ideas for how to tackle livestock’s methane emissions from the inside out.
这项新研究从机械层面证实了这一怀疑，为如何从内到外解决牲畜甲烷排放问题提出了新思路。
In the rumen microbiome, bacteria are essential to cow digestion, but ciliates may not be.
在瘤胃微生物组中，细菌对于奶牛的消化至关重要，但纤毛虫可能不是。
If scientists and farmers could remove or reduce ciliates from the rumen without disrupting digestion too much, they can curb the burp, and with it, methane.
如果科学家和农民能够在不过度干扰消化的情况下去除或减少瘤胃中的纤毛虫，他们就可以抑制打嗝，从而抑制甲烷。
The basic idea goes back decades, Tricarico said, to when rumen microbiologists proposed removing all protozoans — the group of single-celled protists that includes ciliates — from livestock rumens as a potential methane mitigation strategy.
特里卡里科说，这个基本想法可以追溯到几十年前，当时瘤胃微生物学家提出从牲畜瘤胃中去除所有原生动物（包括纤毛虫在内的单细胞原生生物）作为潜在的甲烷减排策略。
But just like on a coral reef or savanna, eliminating predators threw the entire ecosystem out of whack.
但就像在珊瑚礁或稀树草原上一样，消灭捕食者会让整个生态系统陷入混乱。
In experiments, wiping out protozoans allowed bacteria to grow exponentially, which generated more hydrogen and more methane, Mackie said.
麦基说，在实验中，消灭原生动物使细菌呈指数级增长，从而产生更多的氢气和更多的甲烷。
The new study helps identify which specific protozoans, such as isotrichs, are more problematic — producing more hydrogen — than others, he said, offering a more precise target.
他说，这项新研究有助于确定哪些特定的原生动物，例如等丝虫，比其他原生动物更容易产生更多的氢气，从而提供更精确的目标。
Another possibility is to redirect the excess hydrogen away from methanogens.
另一种可能性是将多余的氢气从产甲烷菌中转移出去。
Indeed, other microbes in the rumen consume hydrogen without making methane, but methanogens put up stiff competition.
事实上，瘤胃中的其他微生物消耗氢气而不产生甲烷，但产甲烷菌却面临着激烈的竞争。
By congregating on the ciliates’ surface, right next to the hydrogenobodies, they position themselves to get first dibs on any hydrogen that comes out of the organelles.
通过聚集在纤毛虫的表面，紧邻氢体，它们能够首先获得从细胞器中产生的任何氢。
Now that the new study has clarified the process, “scientists could actually start looking at these hydrogenobodies” themselves as additional targets, Tricarico said.
特里卡里科说，既然新的研究已经阐明了这个过程，“科学家实际上可以开始将这些氢体”本身作为额外的目标。
Take Bovaer, a popular feed additive that reduces cows’ methane emissions — or, in other words, minimizes the methane in their burps.
以 Bovaer 为例，它是一种流行的饲料添加剂，可以减少奶牛的甲烷排放量，换句话说，可以最大限度地减少奶牛打嗝时的甲烷含量。
The synthetic compound, 3-Nitrooxypropanol, interferes with enzymes that produce methane, but it doesn’t work consistently for all cows, diets, and environments.
合成化合物 3-硝基氧基丙醇会干扰产生甲烷的酶，但它并不能对所有奶牛、饮食和环境始终有效。
“This study could actually tell us why it’s not so effective in those other circumstances,” Tricarico said.
“这项研究实际上可以告诉我们为什么它在其他情况下不那么有效，”特里卡里科说。
By detailing the methane-making mechanisms, “you could create circumstances that allow probiotics [or feed additives such as Bovaer] to be more successful.”
通过详细说明甲烷产生机制，“你可以创造让益生菌[或饲料添加剂，如博瓦尔]更加成功的环境。”
While the study has been a leap forward for rumen microbiology, there are a few caveats.
虽然这项研究是瘤胃微生物学的一次飞跃，但也有一些警告。
“This paper, important as it is, still has huge gaps connecting it to methane production,” Mackie said.
麦基说：“尽管这篇论文很重要，但它与甲烷生产之间仍然存在巨大差距。”
While the head-box experiment is helpful, it doesn’t close the case on how different ciliate species, or the hydrogenobodies themselves, contribute to methane emissions.
虽然流浆箱实验很有帮助，但它并没有解决不同纤毛虫物种或氢体本身如何导致甲烷排放的问题。
Importantly, he noted, the authors did not specify the cows’ diet — a primary factor in microbial methane-making, since different feed types result in different amounts of hydrogen gas.
他指出，重要的是，作者没有具体说明奶牛的饮食——这是微生物产生甲烷的主要因素，因为不同的饲料类型会产生不同数量的氢气。
Already, the study has inspired Mackie to explore new research questions.
这项研究已经激发了麦基探索新的研究问题。
Instead of looking at hydrogen transfer between different species of bacteria and methanogens, “I think that now I should be looking at interkingdom hydrogen transfer,” he said, between bacteria, archaea, fungi, and protozoans.
他说，“我认为现在我应该研究细菌、古细菌、真菌和原生动物之间的氢转移，而不是研究不同种类的细菌和产甲烷菌之间的氢转移。”
By looking at the basic biochemistry that underpins these processes, scientists can refine the ways we wrangle methane, from a microscopic organelle, through a teeming ecosystem, and up into the atmosphere.
通过研究支撑这些过程的基本生物化学，科学家们可以改进我们处理甲烷的方式，从微观细胞器到丰富的生态系统，直至进入大气。
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