科学者たちは、数十億年前の岩石の中に私たちの初期の祖先の「失われた世界」を発見した

多国籍研究チームが岩石から古代の原始ステロイドを発見し、複雑な生命が16億年前から存在していたことを示した。 これらの分子は、複雑な生命の進化に関する新たな洞察を提供し、従来の化石記録と脂質化石記録の間の矛盾を調整します。

新たに発見されたいわゆる原始ステロイドの記録は、地球の中世を通じて驚くほど豊富であったことが判明した。 原始的な分子は真核生物の複雑さの初期段階で生成され、化石ステロールの現在の記録は 8 億年前、さらには 16 億年前にまで延長されました。 真核生物は、すべての動物、植物、藻類を含む生命界を指す用語であり、核を含む複雑な細胞構造と、より複雑な分子機構を持つことで細菌から区別されます。

「この発見のハイライトは、真核生物の現在の分子記録の単純な延長ではありません」と、ポツダムのドイツ地球科学研究センター（GFZ）の共同科学者の一人、クリスチャン・ホルマン氏は言う。 「私たち人間を含むすべての現生真核生物の最後の共通祖先が、『通常の』現生ステロールを生成できた可能性が高いことを考えると、これらの希少な特徴を担う真核生物は系統樹の幹に属している可能性が高いです。」

この研究の筆頭著者の一人であるベンジャミン・ネッターシャイム氏は、MARUMの地質分子イメージング研究所で分析された16億4000万年前の岩石サンプルの超解像度元素および分子マップを調べている。 クレジット: MARUM – ブレーメン大学海洋生態学センター。 デスキャンプで

この「切り株」は、真核生物のすべての現存する枝の前駆体である共通の祖先系統を表しています。 その代表的な生物は長い間絶滅していますが、その性質の詳細は、複雑な生命の進化を取り巻く状況にさらに光を当てる可能性があります。 原始ステロイドの何パーセントが希少な細菌源を持っている可能性があるかを評価するにはさらなる研究が必要ですが、これらの新しい分子の発見は、従来の化石の地質学的記録と化石脂肪分子の地質学的記録を一致させるだけでなく、稀で前例のない世界を垣間見ることができます。 . これまでの生活から失われた。 約8億年前の現生化石間質の最初の出現を特徴とする幹群真核生物の競争上の終焉は、ますます複雑化する生命の進化における最も永続的な出来事の1つを反映している可能性がある。

ブレーメン大学マロムのベンジャミン・ニッタースハイム氏は、ブレーメン大学のヨッヘン・ブルックス氏と共同でこの研究を共同執筆したと付け加えた。[{” attribute=””>Australian National University (ANU) – “due to potentially adverse health effects of elevated cholesterol levels in humans, cholesterol doesn’t have the best reputation from a medical perspective. However, these lipid molecules are integral parts of eukaryotic cell membranes where they aid in a variety of physiological functions. By searching for fossilized steroids in ancient rocks, we can trace the evolution of increasingly complex life.”

Dr. Nettersheim inserts a thin section and rock slices of 1.64 billion-years old rocks into the 7T solariX XR FT-ICR-MS equipped with a MALDI source at the Geobiomolecular Imaging Laboratory at MARUM. As part of ongoing research into mid-Proterozoic biomarker signatures at MARUM, GFZ and the Australian National University, Dr. Nettersheim aims to zoom into the cradle of eukaryotic life in unprecedented resolution. Credit: MARUM – Center for Marine Environmental Sciences, University of Bremen; V. Diekamp

Nobel laureate Konrad Bloch had already speculated about such a biomarker in an essay almost 30 years ago. Bloch suggested that short-lived intermediates in the modern biosynthesis of steroids may not always have been intermediates. He believed that lipid biosynthesis evolved in parallel with changing environmental conditions throughout Earth history. In contrast to Bloch, who did not believe that these ancient intermediates could ever be found, Nettersheim started searching for protosteroids in ancient rocks that were deposited at a time when those intermediates could actually have been the final product.

But how to find such molecules in ancient rocks? “We employed a combination of techniques to first convert various modern steroids to their fossilized equivalent; otherwise, we wouldn’t have even known what to look for,” says Jochen Brocks. Scientists had overlooked these molecules for decades because they do not conform to typical molecular search images. “Once we knew our target, we discovered that dozens of other rocks, taken from billion-year-old waterways across the world, were oozing with similar fossil molecules.”

The oldest samples with the biomarker are from the Barney Creek Formation in Australia and are 1.64 billion years old. The rock record of the next 800 million years only yields fossil molecules of primordial eukaryotes before molecular signatures of modern eukaryotes first appear in the Tonian period. According to Nettersheim “the Tonian Transformation emerges as one of the most profound ecological turning points in our planet´s history“. Hallmann adds that “both primordial stem groups and modern eukaryotic representatives such as red algae may have lived side by side for many hundreds of millions of years”. During this time, however, the Earth’s atmosphere became increasingly enriched with oxygen – a metabolic product of cyanobacteria and of the first eukaryotic algae – that would have been toxic to many other organisms. Later, global “Snowball Earth” glaciations occurred and the protosterol communities largely died out. The last common ancestor of all living eukaryotes may have lived 1.2 to 1.8 billion years ago. Its descendants were likely better able to survive heat and cold as well as UV radiation and displaced their primordial relatives.

“Earth was a microbial world for much of its history and left few traces,” Nettersheim concludes. Research at ANU, MARUM and GFZ continues to pursue tracing the roots of our existence – the discovery of protosterols now brings us one step closer to understanding how our earliest ancestors lived and evolved. Shooting at the ancient rocks with a laser coupled to an ultra-high resolution mass spectrometer in MARUM’s globally unique Geobiomolecular Imaging Laboratory, Dr. Nettersheim and his international collaborators aim at zooming into the cradle of eukaryotic life in unprecedented resolution to further improve our understanding of our early ancestors in the future.

Reference: “Lost world of complex life and the late rise of the eukaryotic crown” by Jochen J. Brocks, Benjamin J. Nettersheim, Pierre Adam, Philippe Schaeffer, Amber J. M. Jarrett, Nur Güneli, Tharika Liyanage, Lennart M. van Maldegem, Christian Hallmann and Janet M. Hope, 7 June 2023, Nature.
DOI: 10.1038/s41586-023-06170-w

Participating Institutions:

• Research School of Earth Sciences, The Australian National University, Canberra, Australia
• MARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
• Faculty of Geosciences, University of Bremen, Bremen, Germany
• Université de Strasbourg, CNRS, Institut de Chimie de Strasbourg, Strasbourg, France
• Northern Territory Geological Survey, Darwin, Australia
• German Research Center for Geosciences (GFZ), Potsdam, Germany

MARUM produces fundamental scientific knowledge about the role of the ocean and the ocean floor in the total Earth system. The dynamics of the ocean and the ocean floor significantly impact the entire Earth system through the interaction of geological, physical, biological and chemical processes. These influence both the climate and the global carbon cycle, and create unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society and the marine environment, and in accordance with the Sustainable Development Goals of the United Nations. It publishes its quality-assured scientific data and makes it publicly available. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM cooperates with commercial and industrial partners in accordance with its goal of protecting the marine environment.