This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Iron is one of the most abundant metals on Earth's surface, yet how such massive iron ore deposits formed throughout geological history has long remained a mystery. The prevailing theory has been that ancient photosynthetic bacteria oxidized iron, causing it to precipitate and accumulate in the oceans.
Now, a team of Korean researchers has discovered iron-oxidizing microorganisms and key genes in marine sediments beneath the Antarctic Larsen C Ice Shelf, an environment isolated from light and oxygen. Their experiments confirmed that a key protein encoded by these microbes can oxidize iron, offering new clues to how massive iron formations developed on ancient Earth. The team included Professor Jihyun F.
Min-Jung Kwak from Yonsei University; Professor Hwan Su Yoon from Sungkyunkwan University; Dr. Kyu-Cheul Yoo from the Korea Polar Research Institute; Professor Chung Yeon Hwang from Seoul National University; and Professor Soon-Kyeong Kwon from Gyeongsang National University. They analyzed environmental DNA preserved in marine sediments beneath the ice shelf.
Through metagenomic analysis, they identified a new clade of chemolithotrophic bacteria capable of oxidizing iron(II) in environments where light and oxygen are restricted. They also experimentally demonstrated that the bacterium's Cyc2 protein—a porin-cytochrome fusion protein located in the bacterial outer membrane—acts as a biocatalyst, converting iron(II) to iron(III). This discovery is particularly significant because iron and oxygen are critical elements for understanding Earth's history and the evolution of life.
In particular, massive banded iron formations (BIFs), composed of alternating layers of iron and silica, have long been thought to have formed through the activity of photosynthetic bacteria. However, BIFs from the Cryogenian "Snowball Earth" period of the Neoproterozoic Era, when the planet is believed to have been covered by ice hundreds of meters thick, posed a major challenge to this hypothesis. The research team found crucial clues beneath Antarctic ice shelves.
In 2013, the icebreaking research vessel Araon collected a 2.4-meter-long (7.9-foot-long) Holocene sediment core (GC16B) from the seafloor at a depth of 324 meters (1,063 feet) near the Larsen C Ice Shelf, on the front line of climate change. The research team analyzed the genetic information of the microbiota contained in the environmental DNA from this core. This sedimentary layer preserves records of the marine environment that shifted as the ice shelf changed over a span of about 12,000 years, from the last glacial period of the Quaternary Period in the Cenozoic Era to the present.
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