A drop of seawater contains several million microorganisms, most of which can hardly be called alive, but it is they that can affect the change in the earth's climate. RIA Novosti understands why marine viruses are dangerous and whether it is worth fighting them.
Microorganisms the size of 60 galaxies
In 1989, scientists from the University of Bergen decided to look through a transmission electron microscope at the material precipitated from seawater. The result was stunning: it turned out that about 250 million viruses live in one milliliter of the sample - a hundred times more than was previously thought when virus particles were studied on artificially cultivated bacterial lawns.
“Further work gave even more amazing results. Viruses turned out to be the most numerous organisms living in the oceans - their number goes to quintillions (1030). If we put all the marine viral particles in a chain, it will stretch over 60 galaxies,”says Elena Likhoshvai, Doctor of Biological Sciences, professor, head of the cell ultrastructure department at the Limnological Institute of the Siberian Branch of the Russian Academy of Sciences.
Modern methods of decoding DNA have even more changed the idea of the number and variety of viruses living on the planet. In 2016, scientists from the Joint Genome Institute in California and the National Laboratory. Lawrence at Berkeley analyzed a huge amount of data obtained after metagenomic sequencing of samples from three thousand geographical locations - these were marine, freshwater and terrestrial ecosystems. Researchers have found over 125,000 sections of viral DNA, which has increased the number of known viral genes by 16 times.
Unpretentious and very tenacious
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There are much more microorganisms in the oceans than fish and marine mammals. According to some reports, they account for up to 98 percent of all oceanic biomass. And the most numerous are viruses. They infect 1023 trillions of marine life every second and thus consume up to 20 percent of ocean biomass every day.
At the same time, viruses are distinguished by extreme vitality and unpretentiousness. They can exist over a wide temperature range and under the most unfavorable conditions. For example, the marine diatom virus (Chaetoceros debilis CdebDNAV) continues to infect even at minus 196 degrees Celsius. Cyanophages survive in sediments for up to a hundred years, and the 30,000-year-old giant amoeba Pithovirus sibericum, recently discovered in permafrost, was still capable of infecting microorganisms.
In addition, for a long time it was believed that each virus hunts only a narrow group within the microbial community - bacteria of one kind or another. However, American scientists have shown that marine viruses are not so picky about food and can infect microorganisms of different genera.
No one escapes infection
These numbers and facts do not mean that a vacation at sea borders on suicide. Only one sixtieth of all viral particles found in water are dangerous to humans. Fishes and marine mammals suffer from some, but their main prey is microbes, which play an important role in the formation of the earth's climate.
“It is known that after a virus attack, CRISPR sequences remain in the bacterial genome - small repeating segments of the genome, separated by nontranscribed DNA fragments borrowed from foreign genetic elements. They provide “immunity” to re-infection, and by their presence in the genome of the bacterium, one can conclude that it has already been infected with a certain phage. CRISPR is found in 40 percent of bacteria and 90 percent of archaea,”says Elena Likhoshvay.
Diagram of the life cycle of a marine virus (bacteriophage) / Illustration by RIA Novosti. Alina Polyanina, Depositphotos / logos2012.
According to some reports, cyanobacteria, thanks to which oxygen once appeared on Earth, and other microscopic marine photosynthetics today consume about half of all carbon dioxide released into the atmosphere. Therefore, bacteriophage viruses that attack and destroy them can play a significant role in global warming. However, so far in the scientific world there is no consensus about whether this influence is a plus or minus sign.
Orderlies of the sea
As researchers from the University of Warwick found out, viral infection really affects the photosynthetic abilities of cyanobacteria - the fixation of carbon dioxide (that is, its conversion into carbon compounds) in the bacterial culture slows down almost five times after the attack of bacteriophages. According to rough estimates, as a result of infection of microorganisms in the atmosphere, up to five billion tons of carbon remain unabsorbed annually - this is ten percent of all carbon fixed by the oceans.
However, some scientists point out that after the destruction of bacteria by viruses, the remains of microorganisms are submerged to a depth where the processes leading to the release of carbon dioxide are greatly slowed down. There they secrete iron, phosphorus and some other elements necessary for phytoplankton nutrition. Phytoplankton grows and absorbs more carbon dioxide.
“According to the new scheme of the global circulation of organic matter and biogenic elements of aquatic ecosystems, virioplankton (the totality of all viruses living in the oceans) affects many biogeochemical and ecological processes, including the cycle of nutrition, respiration and distribution of substances in various parts of the ecosystem. In assessing the carbon and nitrogen cycle, it is necessary to take into account the role of viruses, since they are an important part of food webs that regulate global biogeochemical cycles,”sums up Elena Likhoshvai.
Cyanobacteria and other microscopic marine photosynthetics today consume about half of all carbon dioxide released into the atmosphere / Photo: David Savage, Bruno Afonso, Pamela Silver.
Alfiya Enikeeva