微生物如何爬行（1/2）

Recently the New York Times reported the following:

How Microbes Got Their Crawl (1/2)

In the oceans and on land, scientists are discovering rare, transitional organisms that bridge the gap between Earth’s simplest cells and today’s complex ones.

The NYT - By Carl Zimmer - Carl Zimmer covers news about science for The Times and writes the Origins column.

ORIGINS

Feb. 18, 2026

A flurry of new studies is shedding light on one of the biggest steps in the history of life: the evolution two billion years ago of complex cells from simpler ones. In the oceans and on land, scientists are discovering rare, transitional microbes that bridge the gap.

The differences between complex cells, including those in the human body, and simple microbes such as E. coli are stark. Complex cells are packed with compartments; one, known as the nucleus, stores DNA; others, called mitochondria, contain enzymes that generate the cell’s fuel supply. Complex cells are also supported internally by a mesh of filaments, that they use to crawl by breaking down parts of it and building new extensions.

E. coli has none of that: no skeleton, no mitochondria, no nucleus.

These differences, and many others, form one of the deepest divisions in the natural world. Species composed of complex cells are eukaryotes, a group that include animals, plants and fungi, along with protozoans. Simple microbes like E. coli are known as prokaryotes.

Prokaryotes arose more than four billion years ago. Eukaryotes emerged much later, somewhere between 2.5 and two billion years ago. How complex eukaryotes evolved from simpler prokaryotes has left scientists scratching their heads for decades.

In the 1990s, one important clue came from close studies of mitochondria, the fuel factories of the eukaryote cell. Researchers discovered a tiny set of genes inside mitochondria that was not at all like the DNA in the nucleus. Instead, mitochondria have a strong genetic link to bacteria that use oxygen to produce fuel.

That discovery suggested that the ancestors of eukaryotes swallowed oxygen-fueled bacteria and then used them to generate their own fuel. But that insight still left many questions about eukaryotes unanswered. For instance, what sort of organism was the original cell that engulfed mitochondria?

A major clue came in 2015. Scientists extracted fragments of DNA from sediment scooped up from the floor of the Arctic Ocean, and then pieced them together into entire genomes of sediment-dwelling microbes. One turned out to be unlike anything found before: a prokaryote with numerous genes previously found only in eukaryotes.

Among those eukaryote genes were some that were involved in building cellular skeletons. Others help build compartments in which eukaryote cells break down old proteins.

Scientists began looking for other members of this eukaryote-like lineage. The search at first was achingly slow, and most of the discoveries came to light in deep-sea sediments. Scientists named the lineage Asgard, after the home of the gods in Norse mythology.

Brett Baker, a microbial ecologist at the University of Texas at Austin, has spent the last few years speeding up the search. He and his colleagues have gone on Asgard-hunting expeditions to deep-sea sites off the coast of California and in shallow coastal waters in China. Back at their lab, the researchers used powerful new techniques to find DNA from rare microbes.

The search has paid off, as the scientists reported on Wednesday. They found 404 new species of Asgard on their expeditions. They also discovered that databases from previous surveys contained 30 more Asgard genomes that had gone overlooked. All told, in a single study, the scientists have nearly doubled the total diversity of known Asgards.

“We’ve exploded the diversity of Asgards, and there’s no end in sight,” said John Archibald, an evolutionary biologist at Dalhousie University in Canada who was not involved in the new study.

Many of the new Asgard microbes live in the deep sea, but others dwell in coastal waters. But others are land, in habitats ranging from permafrost tundras to lagoons. They may be rare, but they’re also widespread.

“If you can go in your backyard and sequence soil, you’ll get Asgard,” Dr. Baker said.

(to be continued)

Translation

微生物如何爬行（1/2）

在海洋和陸地上，科學家正在發現一些罕見的過渡生物，它們連接著地球上最簡單的細胞和如今複雜的細胞

一系列新的研究正在揭示生命史上最偉大的一步：20億年前，複雜細胞從簡單的細胞演化而來。在海洋和陸地上，科學家正在發現一些罕見的過渡微生物，它們連接著這個進化過程。

複雜細胞, 包括人體內的細胞，與大腸桿菌等簡單微生物之間的差異非常顯著。複雜細胞內部充滿了各種結構；其中一個被稱為細胞核，儲存著DNA；其他結構，例如粒線體(mitochondria)，則含有為細胞提供能量的酵素。複雜的細胞內部由絲狀網支撐，它們透過分解絲狀網的部分結構並建造新的延伸部分來爬行。

大腸桿菌則完全沒有這些結構：沒有骨骼，沒有粒線體，也沒有細胞核。

這些差異以及其他許多差異，構成了自然界最深刻的分類之一。由複雜細胞組成的物種是真核生物 (eukaryotes)，這一類群包括動物、植物、真菌以及原生動物。像大腸桿菌這樣的簡單微生物稱為原核生物 (prokaryotes)。

原核生物出現在40多億年前。真核生物出現得晚得多，大約在25億到20億年前。複雜的真核生物是如何從單純的原核生物演化而來的，幾十年來一直困擾著科學家。

在1990年代，對真核細胞能量工廠, 即粒線體的深入研究帶來了一個重要的線索。研究人員在細胞粒線體內發現了一組與細胞核DNA截然不同的微小基因。相反，粒線體與利用氧氣產生能量的細菌有著密切的遺傳關聯。

這項發現表明，真核生物的祖先可能吞噬了以氧氣為燃料的細菌，並利用它們來產生自己的能量。但這項見解仍留下了許多關於真核生物的未解之謎。例如，最初吞噬粒線體的細胞究竟是什麼樣的生物？

2015年，一項重要的線索出現了。科學家從北冰洋海底採集的沉積物中提取出一些DNA的碎段，並將它們拼接成沉積物中微生物的完整基因組。其中一種微生物與以往發現的任何微生物都截然不同：它是一種原核生物，卻擁有許多先前只在真核生物中發現的基因。

在這些真核生物基因中，有些參與建構細胞骨架，有些則有助於建構隔間以供真核細胞分解舊蛋白質。

科學家開始尋找這種類似真核生物譜系的其他成員。起初，搜尋工作進展極為緩慢，大部分發現都來自深海沉積物。科學家將這一譜系命名為阿斯嘉德（Asgard），取自北歐神話中眾神的居所。

德州大學奧斯汀分校的微生物生態學家Brett Baker在過去幾年裡一直致力於加速搜尋工作。他和他的同事曾多次前往加州海岸的深海區域以及中國沿海的淺海海域進行阿斯嘉德物種的搜尋考察。回到實驗室後，研究人員利用強大的新技術從稀有微生物中尋找DNA。

正如科學家們週三公佈的那樣，搜尋工作取得了豐碩成果。他們在考察中發現了404個新的阿斯嘉德物種。他們也發現，先前調查的資料庫中還包含30個被遺漏的阿斯嘉德基因組。總而言之，僅一項研究就使已知阿斯嘉德物種的多樣性幾乎倍翻了。

並未參與這項新研究的加拿大達爾豪斯大學的進化生物學家John Archibald說道:「我們已經極大地擴大了阿斯加德微生物的多樣性，而且這種探索似乎永無盡頭」。

許多新發現的阿斯嘉德微生物是生活在深海，但也有一些棲息於近海。還有一些生活在陸地上，棲息地涵蓋由永久凍土苔原到潟湖等各種區域。它們或許數量稀少，但分佈範圍卻很廣。

Baker 博士說: 「如果你能在自家後院採集土壤樣本，就能找到阿斯嘉德微生物」。

（待續）

Note:

1. The eukaryotes (真核生物) are the domain of Eukaryota or Eukarya, organisms whose cells have a membrane-bound nucleus. All animals, plants, fungi, seaweeds, and many unicellular organisms are eukaryotes. They constitute a major group of life forms alongside the two groups of prokaryotes(原核生物): the Bacteria and the Archaea. Eukaryotes represent a small minority of the number of organisms, but given their generally much larger size, their collective global biomass is much larger than that of prokaryotes. (Wikipedia)

2. Asgard (阿斯嘉德) is a location associated with the gods in Nordic mythology. It appears in several Old Norse sagas and mythological texts, including the Eddas. (Wikipedia)

3. The Asgard archaea (阿斯嘉德古菌) are a group of microorganisms thought to be closely related to the origin of eukaryotes. When people talk about “members” of this lineage, they usually mean the different phyla (groups) within Asgard archaea that have been discovered so far. Here are some of the main recognized members: Thorarchaeota -Found in marine sediments; has genes linked to protein degradation and metabolism. Odinarchaeota - Less well understood, but part of the early branching Asgard lineages. Heimdallarchaeota - Often considered the closest known relatives to eukaryotes based on genetic data. Helarchaeota -Associated with hydrocarbon metabolism in deep-sea environments. (ChatGPT)