The concept of deep sea usually refers to the ocean below 1000 meters, accounting for 3/4 of the total ocean area, and deep-sea sediments cover more than 50% of the earth's surface. The survival of microorganisms in the deep sea and deep-sea sediments is faced with several extreme environments, such as high pressure, low temperature or high temperature, darkness and low nutritional level, and has long been regarded as a "barren desert". In the mid-20th century, deep-sea survey technology found that there are also high mountains on the deep seabed, and 80,000 kilometers of ridges in the world's oceans are winding. The discovery of mid-ocean ridges makes people realize the unity of marine environment and land environment. 1977, the American submersible Alvin first discovered an independent life system completely independent of photosynthesis in the deep-sea hydrothermal area 2500 meters near the Galapagos Islands in the Pacific Ocean. Located at the bottom of the pyramid of life system are microorganisms, which can directly use low-molecular-weight compounds such as sulfide, nitride and methane ejected from deep-sea craters as food and energy to synthesize various biomacromolecules such as protein and sugar. Located at the top of the pyramid are some large creatures, including worms, worms, clams and mussels, and special biological communities, such as crabs, jellyfish and barnacles. Some people call this colorful and vibrant underwater biological world an "oasis of life" on the seabed. At present, dozens of deep-sea hydrothermal biological systems have been studied. The discovery of the "dark food chain", which relies on the support of the earth's endogenous energy and produces organic matter through chemical combination in the dark and high-temperature environment in the deep sea, has enabled human beings to have a further understanding of the deep sea environment and biosphere. In various extreme environments that have been discovered at present, there are abundant biological resources in the deep sea, the most important of which is deep-sea microorganisms, but most of these microorganisms are still unknown. The study of extreme microorganisms in deep-sea environment is not only one of the most advanced fields of life science at present, but also an important part of the study of deep-sea seabed biosphere and submarine fluid activities. This research will answer the important questions of life science, such as the origin of life, biological evolution and the exploration of life in outer space, and promote the significant development of other disciplines, including earth science, in 2 1 century. In 200 1 year, the National Science Foundation (NSF) published a report entitled "Marine Science in the New Era".

Millenium ",the study of submarine fluid activity is listed as one of the most important frontier research directions of marine science in the next decade, and life science, submarine geophysics and geochemistry will occupy an important position in the above research. The Integrated Ocean Drilling Program (IODP) started from June 5, 2003 to 10, and listed the deep-sea biosphere, seabed and seabed as one of the three major scientific themes of the program. The discovery of deep-sea biosphere is a further understanding of the wide range of biosphere. Although it has been nearly 80 years since the collection of sedimentary columnar samples from the seabed, large-scale systematic research began with the 1968 deep-sea drilling plan. Deep-sea research trilogy such as DSDP, 1968 ~ 1983, ocean drilling (ODP, 1985 ~ 2003) and ocean comprehensive drilling (IODP, 2003 ~ present) are the most important in international geoscience. ODP, an ocean drilling project, shows us another life world from a unique perspective ―― biosphere buried in seabed sediments and crust. There is a huge biota composed of tiny prokaryotes in the deep seabed thousands of meters, and some people estimate that its biomass is equivalent to110 of the global surface biomass. Different from autotrophic microorganisms in hydrothermal vents, prokaryotes in the deep biosphere rely on organic matter in the stratum for heterotrophy. The discovery of the deep-sea biosphere makes people realize that the real foundation of the earth's ecosystem lies in prokaryotes. It is the metabolic processes of these prokaryotes that produce various biogeochemical effects, and on this basis, the earth ecosystem is established. It seems to be a basic law that microorganisms always appear in all physical, chemical and geological environments that can survive. Those microorganisms that grow in extreme environment and usually need to grow normally in this extreme environment are collectively called extreme microorganisms. Extreme environment includes physical extreme environment (such as temperature, radiation, pressure, magnetic field, space, time, etc. ), chemical extreme environment (such as dryness, salinity, pH value, heavy metal concentration, redox potential, etc. ) and biological extreme environment (such as nutrition, population density, biological chain factors, etc. ), and the seabed is considered to be the extreme in the above extreme environment. There are acidophilic (below pH3), alkalophilic (above pH 10), halophilic (above 25mol/L), psychrophilic (below 0℃), thermophilic (above 120℃) and positive pressure (above 500 atmospheres) microorganisms in the deep-sea environment. The study of extreme biological characteristics of deep-sea environment also provides good biological materials for the study of life limit, and constantly provides new clues and basis for exploring life in outer space. Scientists imagine that since microorganisms can survive well in such a harsh and extreme environment, there will also be life on Mars. The establishment of deep-sea microbiology dates back to 1970s. Professor Yayanos of Scripps Institute of Oceanography in the United States designed and improved a high-pressure culture tank, and isolated deep-sea barotropic bacteria at 1979. 1989, Bartlett first isolated the pressure-regulated outer membrane protein (OmpH). 1990, Mitsubishi heavy industries and sanyo company of Japan began to develop a high-temperature and high-pressure culture system for deep-sea microorganisms for Japan marine science and technology center, which was completed in 1994 and cost 750 million yen. The construction of this system and the construction of deep diving sampling system have greatly promoted the research progress of deep-sea biosphere. 1995 Kato et al. analyzed a pressure regulating gene cluster. 1999 Nogi et al. isolated and identified an extremely barotropic bacterium Moritella Yayanosii [1 ~ 3] from Mariana trench. In 2003, Japan, the United States and Italy successively introduced deep-sea barotropic bacteria DSS 12 and photobacter.

Profundum SS9 whole genome sequencing [4,5]; In March, 2005, Science [6,7] published the whole genome sequence and preliminary analysis of SS9 of Fusarium profundum. Deep-sea microorganism research has great economic and social value besides scientific research value, and has been widely concerned. Deep sea creatures are in a unique physical, chemical and ecological environment. Surrounded by high hydrostatic pressure, severe temperature gradient, extremely weak light conditions and high concentration of toxic substances, they form a very special biological structure and metabolic mechanism system. Due to this extreme environment, all kinds of active substances in deep-sea organisms, especially enzymes, have the characteristics of high temperature resistance, acid and alkali resistance, salt resistance and strong anti-toxicity. These special bioactive substances are the most valuable parts of deep-sea biological resources. In addition to developing and improving the isolation and culture methods of marine microorganisms to obtain new marine microorganisms and screen active substances, it is an inevitable and effective choice to explore marine microbial resources, especially deep-sea microbial resources, and to develop new marine drugs, which is also a hot spot in the development of deep-sea microbial resources. To sum up, deep-sea creatures have potential application value in the following aspects:

1 industrial application

Industrial production often requires some special reaction temperature, pH value and adding some organic solvents. Under this condition, ordinary enzymes can't keep their activity. Therefore, industries that rely on enzymes must spend a lot of money and adopt special processes to keep the activities of these enzymes, which greatly increases the cost. Extreme enzyme can still maintain high activity under the condition of inactivation of common enzyme, so it has broad application prospects in industry. At present, several extreme enzymes, such as high-temperature polymerase, sugar enzyme, amylase and protease, have started industrial production and created billions of dollars in economic benefits.

2 Medical application

It has a long history to develop drugs from organisms to treat various human diseases. Because more and more pathogenic bacteria or viruses are resistant to the current drugs, new diseases are constantly emerging. Therefore, screening new biological drugs from the ocean has become the direction of marine drug research and development. Due to the uniqueness of the environment, deep-sea creatures have become the source of new special drugs such as anti-tumor, anti-virus, blood pressure lowering and blood lipid lowering. At present, there are not many reports on deep-sea drug screening in the world, but it can be predicted that its prospects will be very broad.

3 Environmental protection

At the bottom of the sea, due to the accumulation of animal carcasses and volcanic eruptions, the concentration of toxic substances, sulfides and other substances harmful to terrestrial organisms is very high, and microorganisms living here can decompose these substances and use them as energy to thrive. Therefore, these organisms have important application value in removing heavy metals, oil and other pollutants on the earth's surface. At present, Japanese scientists have screened strains with high oil decomposition ability from deep sea and conducted application research. Since the late 20th century, with the improvement of deep-sea technology, more and more countries have devoted themselves to the frontier field of deep-sea research. At present, the diving depth of deep-sea manned submersible reaches 6500m, and the diving depth of unmanned cable-controlled submersible ROV can reach11000m. Deep-sea sediment samples are obtained in the deepest Mariana Trench. It was found that the microbial content reached 103 ~ 104/g. The laboratory simulation of deep-sea environment also made a breakthrough, and extreme microorganisms such as barophilic, alkalophilic, acidophilic, halophilic, psychrophilic and thermophilic were isolated and identified. At present, the countries that carry out deep-sea microbial research in the world are mainly distributed in Europe, America and Asia, among which the United States, Japan, Germany and France are the main forces in deep-sea microbial research. At present, some progress has been made in the isolation and culture of deep-sea microorganisms, diversity investigation, functional gene research and adaptive mechanism research (such as halophilic mechanism of deep-sea halophilic bacteria). Various extreme microorganisms have also made breakthroughs in the development and application of industrial enzymes, tool enzymes, environmental remediation and bioactive substances, which has made people see the great potential and broad application prospects of deep-sea microbial development. Deep-sea biological resources, especially microbial resources, have been paid more and more attention by human beings. With the development of science, the improvement and perfection of underwater engineering technology and detection technology, human beings have greater space and possibility for the research and development of deep-sea microorganisms. The systematic research of deep-sea biological genes in China started late, and it has been mainly funded by the Ministry of Science and Technology and China Ocean Engineering since this century. Based on the Third Institute of Oceanography of the State Oceanic Administration, China Oceanographic Association established the China Ocean Biogene Research and Development Base, and developed and equipped a number of special equipment for deep-sea microbial culture in ocean and laboratory. With the support of deep-sea equipment, real deep-sea microbial research can be carried out. Up to now, the basic research mainly focuses on the role of deep-sea microorganisms in the material cycle; Isolation and culture of extremophiles; Genetic metabolism of microorganisms, adaptation mechanism of microorganisms in extreme environment of deep sea. Various halophilic, thermophilic, psychrophilic, halophilic, alkalophilic and acidophilic microorganisms in the deep sea were successfully isolated and identified, and many new species were discovered. On this basis, China's first deep-sea microbial strain resource bank is under construction. A variety of deep-sea extreme enzyme genes were cloned, expressed and analyzed. Screening antibacterial and antitumor active substances from deep-sea microorganisms has also been carried out. The deep-sea pressure-resistant strain comra WP3 has basically completed the whole genome sequencing, and post-genome research is under way. The metagenomic library of deep-sea sediments was constructed, and the cosmid gene library of deep-sea sediments with a depth of 5000 meters was successfully constructed. Through the analysis of the clones, it was found that the microbial sources in the library were mainly some uncultured new microbial species, and the sequencing of some clones found that most of the genes in the clones were new genes. At present, several clones expressing bioactive substances have been screened and their sequences are being determined. In a word, deep-sea biological research is a high-input project relying on engineering technology, and the rapid development of deep-sea biological gene resources development and utilization research in China needs more funds and talents.