内容来源：https://www.quantamagazine.org/a-new-way-that-a-cows-inner-world-shapes-earths-atmosphere-20260727/

内容总结：

《细胞内部新发现：奶牛瘤胃原生动物中的“氢体”或成气候治理关键》

据《科学》杂志最新研究，科学家在奶牛肠道微生物中发现了一种此前未知的细胞器——被命名为“氢体”（hydrogenobody）。这一发现为理解畜牧业甲烷排放机制提供了全新视角，或将为减缓全球变暖开辟新路径。

每头牛的瘤胃都是一个庞大的发酵系统，其中生活着数以千万计的微生物，包括细菌、真菌和纤毛虫。其中，纤毛虫作为顶级捕食者，在分解饲料过程中产生氢气，而这些氢气随后被产甲烷菌转化为强效温室气体——甲烷。据估算，反刍动物（牛、山羊、绵羊等）通过打嗝排放的甲烷占大气甲烷总量的约三分之一，在过去150年间贡献了约30%的全球升温效应。

研究团队对450种瘤胃纤毛虫进行了基因组测序，发现其细胞膜边缘存在一种特殊的单层膜结构，内部含有氢化酶。这种名为“氢体”的细胞器专门负责产生氢气，并为纤毛的运动提供能量。电子显微镜图像显示，不同种类的纤毛虫“氢体”数量差异显著：体型较大的等毛类纤毛虫（Isotrichs）表面密布“氢体”，而内毛类纤毛虫（Entodinomorphs）仅在特定区域分布。

通过“头箱”气体测量装置对100头奶牛的实际监测证实：瘤胃中等毛类纤毛虫较多的奶牛，其甲烷排放量显著高于内毛类纤毛虫占优的个体。这一结果从分子机制层面证实了科学界长期以来的推测——纤毛虫与甲烷排放密切相关。

研究指出，传统观点认为只需抑制产甲烷菌即可控制甲烷排放，但新发现提示，产甲烷菌实际上是通过在纤毛虫表面聚集，优先获取“氢体”释放的氢气。这意味着，未来可更精准地靶向特定纤毛虫种类（如等毛类）或其“氢体”，从而在不过度影响消化功能的前提下遏制甲烷生成。

该研究还为评估现有减排方案提供了新思路。以常见饲料添加剂Bovaer为例，其作用机理是干扰产甲烷酶活性，但实际效果因奶牛个体、饲料类型和环境而异。研究人员表示，通过厘清甲烷生成的完整生物链条，可优化益生菌或添加剂的使用条件，提升减排效率。

不过，专家也指出，该研究在纤毛虫种类与甲烷排放的具体关联、实验奶牛日粮控制等方面仍存在空白。未来，科学家需进一步解析瘤胃微生物群落的协同机制，从种间氢转移等微观层面入手，将基础生物化学发现转化为可落地的气候治理方案。

中文翻译：

牛的内心世界塑造地球大气层的新方式
沈泽君/《Quanta Magazine》
每头牛的体内都存在着一个繁盛的生态系统。在其肠道深处，有一个被称为瘤胃的巨大发酵室，这里栖息着强大的微生物群落，每天能够消耗多达100磅的饲料。在这个胃肠囊内，数以千万计的细菌搜寻着纤维、淀粉和其他营养物质的残渣，分解纤维素和蛋白质。微生物真菌助其一臂之力，其酶能摧毁坚硬的细胞壁，而这一切的统治者是纤毛虫：体型庞大、以细菌为食的掠食性微生物。
这个复杂的食物网将大量化合物转化为能量，为牛的代谢提供动力。几乎没有浪费：即便是发酵的副产品——氢气和二氧化碳，也被这个黑暗、温暖、无氧世界中的机会主义者所利用。这些机会主义者是被称为产甲烷菌的瘤胃微生物，它们的代谢废物是甲烷，一种臭名昭著的强效温室气体。
就这样，牛的内心世界具有了全球意义。包括牛、山羊和绵羊在内的反刍动物，通过打嗝排出了大气中约三分之一的甲烷。总体而言，当甲烷与来自垃圾填埋场和化石燃料的更多甲烷结合时，它约占过去150年全球气温上升原因的30%。但它有一个弱点：它比二氧化碳分解得更快。这就是为什么牛的气体排放引起了全球研究人员的兴趣。他们正在研究家畜特化的胃，以识别产生甲烷的生物学机制，这些机制可能成为在我们有生之年减缓全球变暖的靶标。
最近发表在《科学》杂志上的一项研究揭示了一个藏在膜中的线索。在对450种纤毛虫（瘤胃中的顶级捕食者）的新基因组序列进行分析时，研究人员循着一条线索发现了一种对科学界来说全新的细胞器，这种细胞器对于将原子重新构建成导致地球变暖的化合物的生化过程至关重要。他们将其命名为“氢化体”，因为它产生氢气，而产甲烷菌随后将氢气转化为甲烷。
这些发现为管理这种普遍的变暖源提供了新思路，胡安·特里卡里科（Juan Tricarico）说。他在乳业管理公司（Dairy Management Inc.，一家为奶牛养殖户服务的非营利性行业协会）研究肠道甲烷，并未参与最近这项研究。“仅仅针对产甲烷菌可能还不够。”
他补充说，要理解微生物如何导致行星尺度的变化，需要进一步厘清瘤胃中的微生物食物网以及它们产生甲烷的具体机制。“我们想了解这些微生物繁衍生息的环境。”
甲烷是如何产生的
尽管纤毛虫已被研究了一个多世纪，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一直被忽视。微生物学家知道它们是瘤胃中最大的单细胞生物。在显微镜下，它们毛发状的纤毛像轻柔的扫帚一样扫过细胞外的区域，将细菌拉入口中并推动它们。为所有这些纤毛提供动力需要大量能量，而制造这种能量会释放氢气，然后被细菌和古菌（包括产甲烷菌）消耗。
“整个瘤胃系统高度进化、高度协同、高度共生，并且已经演化到消耗所有氢气的程度，”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。“而它们（产甲烷古菌）通过将这些氢气转向主要产甲烷途径来做到这一点。”
为了更好地理解瘤胃纤毛虫在甲烷排放中的具体作用，微生物学家转向了基因组学。2021年，俄亥俄州立大学的瘤胃微生物学家于忠堂对第一种瘤胃纤毛虫——尾状内毛虫（Entodinium caudatum）的基因组进行了测序；其属类约占家畜瘤胃中所有纤毛虫的90%。几年后，于忠堂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——这是一个良好的开端，但远不足以代表牛微生物组中纤毛虫的多样性。
因此，当2026年发表在《科学》杂志上的研究报告了450个新的纤毛虫基因组序列时，瘤胃微生物学界一片哗然。（该研究的作者大多来自中国科学院或南京农业大学，他们未回应《Quanta Magazine》的采访请求。）这些基因组已添加到一个数据库中，任何研究人员都可以访问和研究这些纤毛虫的序列。
该论文的作者们领先一步，在基因组中搜索了产生甲烷的酶（包括催化氢气形成的氢化酶）的基因序列。他们发现，一些纤毛虫的氢化酶与已知存在于所有生命形式中的酶的所有版本都不同。定位这些不寻常酶的实验发现，它们也位于一个不寻常的地方：就在细胞膜的边缘。
几种主要纤毛虫的电子显微镜图像揭示了原因。在外层细胞膜内衬上，纤毛的基部，是一些简单的结构，每个结构都由单层膜包围。内部是氢化酶。这些纤毛虫似乎拥有细胞器，即新描述的氢化体，它们被专门放置在为纤毛提供能量的位置。
马克·贝兰/《Quanta Magazine》
从最基础的角度来说，细胞器是一种具有特化功能的膜结合结构，“被认为拥有与细胞内任何其他物质不同的分子特征”，未参与这项研究的芝加哥大学细胞生物学名誉教授亚伦·特克维茨（Aaron Turkewitz）说。与细胞核和线粒体一样，氢化体符合这一描述。“发现一种新的细胞器非常令人兴奋，”他说。
当该研究的作者进一步观察时，他们注意到一些纤毛虫比其他纤毛虫拥有更多的氢化体。其中一种突出的类型——等毛虫（Isotrichs），“体型巨大”，特里卡里科说，至少按微生物标准来看是这样。它们覆盖着类似皮毛的纤毛，并且细胞膜上有更多的氢化体来为这些纤毛提供能量。另一方面，内毛虫（Entodinomorphs）体型较小，纤毛和氢化体仅存在于某些区域。每种类型的纤毛虫在瘤胃中占据不同的生态位，就像狮子与猎豹在热带草原上扮演不同的捕食者角色一样，特里卡里科说。
在这种细胞器内部，氢化酶不仅因其在氢气生产中的作用而备受关注；它还消耗氧气。这一作用也有助于产甲烷菌，因为它们会受到氧气的抑制。因此，氢化体不仅为产甲烷菌提供原料，还有助于保持瘤胃这个黑暗洞穴的无氧环境，使产甲烷菌得以繁衍生息。
这些产生氢气的细胞器似乎是甲烷拼图的一部分，这听起来很合理，但为了确定这一点，研究人员需要知道它们是否会对甲烷产量产生显著影响。为了验证这一点，他们使用一种名为“头箱”的气体测量设备，测量了100头奶牛的甲烷排放量——这个设备正如其名：一个围住奶牛头部的箱子，用于测量其打嗝排放的甲烷。然后他们分析了奶牛瘤胃中等毛虫和内毛虫的组成。他们发现，等毛虫（因此也是氢化体）数量更多的奶牛，其甲烷读数远高于那些微生物组以内毛虫为主的奶牛。
科学家们早就怀疑纤毛虫与甲烷排放有关，于忠堂说。这项新研究从机制层面证实了这一怀疑，并为如何从内部解决家畜的甲烷排放问题提出了新思路。
从细胞器到大气层
在瘤胃微生物组中，细菌对牛的消化至关重要，但纤毛虫可能并非必需。如果科学家和农民能够在不严重干扰消化的情况下从瘤胃中去除或减少纤毛虫，他们就可以抑制牛的打嗝，从而减少甲烷。
这个基本想法可以追溯到几十年前，特里卡里科说，当时瘤胃微生物学家提议从家畜瘤胃中移除所有原生动物（包括纤毛虫在内的单细胞原生生物的群体），作为潜在的甲烷减排策略。但就像在珊瑚礁或热带草原上一样，消除捕食者会使整个生态系统失衡。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甲烷，麦基说。这项新研究有助于确定哪些特定的原生动物（例如等毛虫）比其他原生动物问题更大——产生更多氢气——从而提供了更精确的目标，他说。
另一种可能的方法是将多余的氢气从产甲烷菌那里转移走。事实上，瘤胃中的其他微生物消耗氢气而不产生甲烷，但产甲烷菌竞争激烈。通过聚集在纤毛虫的表面，紧挨着氢化体，它们可以确保优先获得从这些细胞器中释放出的任何氢气。既然这项新研究已经阐明了这一过程，“科学家实际上可以开始研究这些氢化体”本身作为额外的靶标，特里卡里科说。
以Bovaer为例，这是一种流行的饲料添加剂，可减少奶牛的甲烷排放——或者换句话说，最大限度地减少它们打嗝中的甲烷。这种合成化合物3-硝基氧丙醇会干扰产生甲烷的酶，但并非对所有奶牛、日粮和环境都同样有效。“这项研究实际上可以告诉我们，为什么它在其他情况下效果不佳，”特里卡里科说。通过详细说明甲烷产生的机制，“你可以创造出使益生菌（或像Bovaer这样的饲料添加剂）更成功发挥作用的条件。”
尽管这项研究是瘤胃微生物学的一个飞跃，但仍存在一些注意事项。“这篇论文虽然重要，但在将其与甲烷产生联系起来方面，仍存在巨大空白，”麦基说。虽然头箱实验有帮助，但它并未最终确定不同种类的纤毛虫或氢化体本身如何对甲烷排放做出贡献。他指出，重要的是，作者没有说明奶牛的日粮——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。
这项研究已经激发了麦基探索新的研究问题。他不再关注不同种类细菌和产甲烷菌之间的氢气转移，“我认为现在我应该关注跨界的氢气转移，”他说，即细菌、古菌、真菌和原生动物之间的转移。
通过研究支撑这些过程的基础生物化学，科学家们可以完善我们控制甲烷的方式——从一个微观的细胞器，途经一个生机勃勃的生态系统，最终进入大气层。

英文来源：

A New Way That a Cow’s Inner World Shapes Earth’s Atmosphere
Ada Zejun Shen/Quanta Magazine
Within every cow is a thriving ecosystem. 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. Inside this gut pouch, tens of millions of bacteria scavenge for scraps of fiber, starch, and other nutrients, and break down cellulose and proteins. 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.
This complex food web transforms a bounty of compounds to fuel the cow’s metabolism. 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. Those opportunists are rumen microbes called methanogens, and their waste product is methane, a notoriously powerful heat-trapping greenhouse gas.
In this way, the inner world of a cow has global significance. Ruminant livestock, including cows, goats, and sheep, have burped out about a third of all methane gas in the atmosphere. 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. But it has a weak spot: It decays more quickly than carbon dioxide. That’s why cow gas has attracted interest from researchers across the globe. 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.
A recent study published in Science has revealed a clue wrapped in a membrane. 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. They named it the “hydrogenobody” because it produces hydrogen gas, which methanogens then turn into methane.
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. “Just targeting the methanogens is probably not enough.”
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. “We want to understand the environment under which these microbes thrive.”
How the Methane Gets Made
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. Microbiologists know they are the largest single-celled organisms in the rumen. Under a microscope, their hairlike cilia sweep the area outside the cell like wispy brooms, pulling bacteria into their mouths and pushing them around. 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.
“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. “And they [methanogenic archaea] do it by shunting that into mainly methanogenesis.”
To better understand the specific roles of rumen ciliates in methane emissions, microbiologists have turned to genomics. 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. 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.
So when the 2026 study in Science reported 450 new ciliate genome sequences, jaws dropped across the rumen microbiome community. (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.
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. They found that some of the ciliates’ hydrogenases were different from all known versions of the enzymes found across life. Experiments to locate these unusual enzymes found them in an unusual place, too: right at the edge of the cell membrane.
Electron microscope images of several prominent ciliate species revealed why. Lining the outer cell membrane, at the base of the cilia, were simple structures, each encircled by a single membrane. Inside was hydrogenase. The ciliates seemed to have organelles, the newly described hydrogenobodies, specially placed to provide energy to cilia.
Mark Belan/Quanta Magazine
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. The hydrogenobody, like the nucleus and mitochondria, fits this description. “Finding a new organelle is pretty exciting,” he said.
When the study’s authors looked closer, they noticed that some ciliates had more hydrogenobodies than others. Isotrichs, one prominent type, are “huge,” Tricarico said, at least by microbial standards. They are covered in cilia that resemble fur and have far more hydrogenobodies on their cell membrane to fuel those cilia. Entodinomorphs, on the other hand, are smaller, with cilia and hydrogenobodies only in certain areas. 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.
Within the organelle, the hydrogenase enzyme isn’t just interesting for its role in hydrogen production; it also uses up oxygen. This action supports methanogens, too, since they are inhibited by oxygen. 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.
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. 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. Then they analyzed the composition of isotrich and entodinomorph ciliates within the cows’ rumens. They found that cows with more isotrichs — and therefore more hydrogenobodies — had much higher methane readings than those whose microbiomes were dominated by entodinomorphs.
Scientists have long suspected that ciliates are associated with methane emissions, Yu said. 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.
From Organelle to Atmosphere
In the rumen microbiome, bacteria are essential to cow digestion, but ciliates may not be. 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.
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. But just like on a coral reef or savanna, eliminating predators threw the entire ecosystem out of whack. In experiments, wiping out protozoans allowed bacteria to grow exponentially, which generated more hydrogen and more methane, Mackie said. 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.
Another possibility is to redirect the excess hydrogen away from methanogens. Indeed, other microbes in the rumen consume hydrogen without making methane, but methanogens put up stiff competition. 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. Now that the new study has clarified the process, “scientists could actually start looking at these hydrogenobodies” themselves as additional targets, Tricarico said.
Take Bovaer, a popular feed additive that reduces cows’ methane emissions — or, in other words, minimizes the methane in their burps. The synthetic compound, 3-Nitrooxypropanol, interferes with enzymes that produce methane, but it doesn’t work consistently for all cows, diets, and environments. “This study could actually tell us why it’s not so effective in those other circumstances,” Tricarico said. By detailing the methane-making mechanisms, “you could create circumstances that allow probiotics [or feed additives such as Bovaer] to be more successful.”
While the study has been a leap forward for rumen microbiology, there are a few caveats. “This paper, important as it is, still has huge gaps connecting it to methane production,” Mackie said. 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. 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.
Already, the study has inspired Mackie to explore new research questions. 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.
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.