Marine archaea

Approaching the archaea

  Life on Earth is colorful. In the past, people mainly divided life into eukaryotes (consisting of eukaryotic cells, with a nucleus) and prokaryotes (consisting of prokaryotic cells, without a nucleus, but with a nucleus). We humans, animals and plants are all eukaryotic organisms; while bacteria are prokaryotes because they do not have a nucleus.
  In recent years, scientists have discovered that there is still a group of magical microorganisms living on the earth. They have both a cell structure and metabolism similar to those of bacteria, and a genetic transcription system similar to that of eukaryotes. In 1977, American scientist Carl Woese first defined this type of microorganism as archaea, different from bacteria and eukaryotes; in 1990, Carl Woese further divided life on earth into three forms, namely archaea. , bacteria and eukaryotes.
  Archaea were originally thought to live only in extreme environments, such as submarine hydrothermal vents, terrestrial hydrothermal vents, and saline lakes. With the deepening of research, scientists have found that many archaea also live in other natural environments, such as the ocean, soil, and even non-extreme environments such as the intestines of humans and animals. Among them, the ocean accounts for about 71% of the earth’s area and is one of the largest ecosystems in the world. Archaea are widely distributed in various marine environments, especially in the dark water and sediment environments of the deep sea, and are the main members of marine microorganisms. one.

  According to the “identity card” carried by the archaea, the 16SrRNA gene, scientists have divided the marine archaea into three main categories: the phylum Mycoarcha (Marine Archaea-I, MG-I), Marine Archaea-II ( MG-II) and Marine Archaea-III (MG-III). Currently, more than 20 different archaea have been detected in the marine environment, with wide distribution and high abundance.
  ”I’m born to be useful.” There are a large number of archaea in the ocean. What role do they play in nature? What can humans learn from archaea?
  The study found that some marine archaea are good at oxidizing ammonia to produce nitrite, some can metabolize methane to affect the global climate, and some have been found to be closely related to the origin of eukaryotes. Therefore, the study of marine archaea can lay a solid foundation for us to learn more about the mechanism of the earth’s element cycling, respond to global climate change, and reveal the origin of eukaryotes.

Ammonia-oxidizing archaea and nitrogen elements

  Ammonia Oxidizing Archaea (AOA) generally lives in mild and extreme environments, and is highly abundant in seawater, belonging to the phylum Oxidizing Archaea.
  When it comes to the effect on the nitrogen cycle of the earth, ammonia-oxidizing archaea definitely have a place. Ammonia-oxidizing archaea and ammonia-oxidizing bacteria (AOB, AmmoniaOxidizingBacteria) have similar functions, and can oxidize ammonia (NH3) to nitrite (NO2?), a process called ammonia oxidation, which is the first step of nitrification. Other microorganisms can further oxidize nitrite to nitrate (NO3?), completing the second step of nitrification. In addition, there are some microorganisms that can reduce nitrate or nitrite to form nitric oxide (NO), nitrous oxide (N2O) or nitrogen gas (N2), that is, denitrification.
  Ammonia-oxidizing archaea not only live in the ocean, but are also widely distributed in soil, sewage treatment plants and even our daily garbage permeate. Recent studies have found that some ammonia-oxidizing archaea can continue ammonia oxidation by producing their own oxygen in an oxygen-deficient environment.
  Through nitrification and denitrification, nitrogen can flow “healthily” between ecological environments at all levels, and ultimately maintain a good ecological cycle. Ammonia-oxidizing archaea is one of the most important converters, silently giving away in corners we don’t know or pay attention to.

Methanogenic archaea influencing global climate

  The species of archaea in marine sediments are very diverse, including the phylum Proteobacteria, the phylum Ussarchaea, and the phylum Broadarchaea. One of the main ways in which archaea participate in the carbon cycle is methane metabolism.
  Methane is the most important greenhouse gas, and its increase will cause global warming and cause a series of environmental problems. Therefore, the normal flow of methane is particularly important, and this process is controlled by some microorganisms, including methane-metabolizing archaea.
  Methane-metabolizing archaea mainly belong to the phylum Broadarchaea, which can be divided into methanogenic archaea and methane-oxidizing archaea according to different functions. Methanogenic archaea can form methane in an anaerobic environment. The substrates (substances involved in biochemical reactions) of methanogenic archaea include: hydrogen (H2), carbon dioxide (CO2), acetate and methyl compounds.
  Recently, Chinese scientists discovered for the first time a methanogenic archaea that can “eat oil”, that is, the archaea can directly degrade petroleum hydrocarbons to produce methane, which is expected to “revive” some old oil fields. Methane-oxidizing archaea oxidize methane to carbon dioxide (CO2) as their own carbon source and energy supply.
  It is thought that Urus archaea may have a symbiotic relationship with methanogenic archaea, and the compounds such as hydrogen and acetic acid produced by its fermentation will maintain the growth of methanogenic archaea. In return, the Urus archaea would get some of the amino acids and other compounds produced by the methanogenic archaea. It is the various types of archaea in marine sediments that cooperate and “give” to each other that make them play an integral role in the carbon cycle.

Asgard archaea – in search of the origin of eukaryotes

  The origin of mankind has always been a scientific mystery that haunts us. To understand this question, we first need to understand how eukaryotic cells evolved and what were their ancestors?
  In recent years, Asgard archaea, found in deep-sea hydrothermal vents and mangrove wetland sediments, are considered to be the closest prokaryotes to eukaryotes. Scientists believe that they are most likely ancestors of eukaryotes, which means that eukaryotes may have originated from Asgard archaea.
  The reason is that Asgard archaea not only have the biological characteristics of prokaryotes, such as archaea do not have a nucleus, so they belong to prokaryotes; but interestingly, Asgard archaea also has many transition from prokaryotic to eukaryotic. Biological characteristics, such as: Asgard archaea are rich in many protein-coding genes that are only found in eukaryotes.
  In addition, archaea are also similar to eukaryotes in the transmission of genetic information such as genome replication, transcription and translation, and these evidences gradually make “an archaeal host cell and an α-proteobacteria (mitochondria) endosymbionts fused together, resulting in a The first eukaryotic cell”, the “endosymbiotic hypothesis” of the origin of eukaryotes is becoming more and more convincing.
  The newly discovered Wukong archaea (named after the Chinese mythical character Sun Wukong) by the team of Professor Li Meng of Shenzhen University has given a new understanding of the origin of eukaryotes. They speculate that the Wukong-Heimdall archaea may be the ancestor of eukaryotes . But where did we come from? This question may only be answered in future research.
  As the main components of marine microorganisms, marine archaea play a key role in the global cycle of nitrogen, carbon, and sulfur, and their relationship with eukaryotes is also amazing. However, due to the limitations of the living environment of some marine archaea and the limitations of current isolation and culture techniques, the archaea that have been discovered are only the tip of the iceberg, and the archaea that have been successfully isolated and cultured are even rarer.
  The influence of marine archaea on the global ecosystem inspires people to protect the marine environment, make full use of the diversity of marine microorganisms, regulate atmospheric climate, and combine other disciplines to reveal other element cycles involved in marine archaea. Studying some marine archaea living in extreme environments will also help to understand the ancient environment and evolution of the earth, and get a better explanation of the origin of eukaryotes.

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