Unexpectedly, their prey has rewritten the marine food chain
Our reporter Fu Lili
We all know that there is a classic food chain of "algae-protists-fish" in the ocean. For a long time, viruses seem to be outside the classic food chain. Recently, scientists have finally discovered that the protists feed on viruses, which allows the virus to enter the classic food chain. .
According to media reports, in the Gulf of Maine and the Mediterranean Sea, researchers collected 1,698 protist samples and performed DNA sequence analysis on these samples.
They used single-cell genome analysis, and their sequencing results can indicate the presence of microorganisms and viruses.
The results showed that in 51% of the protist samples from the Gulf of Maine and 35% of the samples from the Mediterranean, viral DNA was detected, and in the samples of the two types of protists, dermocysts and synechinoids, each An individual contains viral DNA.
This allows scientists to finally have evidence that virus-eating protists do exist.
The research results were published in "Frontiers in Microbiology".
This is known in the industry as the discovery of "rewriting the marine food chain".
So, what kind of organisms feed on viruses, how did scientists discover them, and why do viruses do no harm to them?
Biologists have been looking for organisms that eat viruses
For a long time, it seems that viruses only infect and lyse to kill organisms, and are not regarded as food by organisms, which seems unreasonable.
So biologists have been looking for organisms that eat viruses.
Liang Yantao, an associate professor of the School of Life Sciences, Ocean University of China, introduced in an interview with a reporter from the Science and Technology Daily that in 1993, the Canadian scientist Curtis Sattle's research group discovered that viruses and fluorescent particles of similar size can be preyed by protists. They will Viruses and pellets are labeled with fluorescence, and then protists are added to detect the speed at which the virus and fluorescent pellets are cleared in seawater to reflect the efficiency of predation by protists. It was found that large-particle viruses are more likely to be preyed and digested by protists.
And the virus may contribute 0.2%-9% of the carbon, 0.3%-14% of the nitrogen, and 0.6%-28% of the phosphorus in the protists’ food.
Subsequent studies have also found that certain protists can prey on viruses, and can simultaneously ingest the viruses in the bacteria and on the surface of the bacteria while preying on bacteria.
But the current research in this area is still very limited.
"At present, it has been found that viruses are mainly preyed by protists that eat relatively small'organs'. Generally speaking, the size of the virus is about 100 nanometers, and the size of the'organs' that can eat the virus is about 10 times the size of the virus. Liang Yantao said that previous studies by other scientists have found that the "organs" eaten by skin gallworms are very small, not large enough to eat bacteria, and it is more than enough to eat viruses.
Therefore, it is speculated that such protists may directly swallow and prey viruses.
In this report, researchers have detected viral DNA sequences in the single-cell genomes of many different types of protists. Especially in the two types of protists, synagogues and dermatocysts, the number of viral sequences is relatively high.
In addition, an interesting phenomenon is that these two types of protists contain a large number of viral DNA sequences, but bacterial DNA sequences are few.
This eliminates the possibility of "free-riding"-some protists may feed on bacteria, and viral phages will be parasitic in the bacteria, and the bacteria will be eaten by the protists.
Why did they eat the virus and were not killed by the virus?
"Previously, scientists believed that protists may ingest bacteria and other microbial particles into the body through phagocytosis, and ingest bacteria and microalgae while ingesting viruses on their cell surfaces and cells." Liang Yantao said, and this The results of this study speculate that the two types of protists, dermatoglyphids and synechinoids, may directly swallow and prey on viruses, which is another way for protists to prey on viruses, independent of the predation of viruses by protists with microorganisms.
At this point, some readers may ask, humans will get sick if they are infected with the virus, and these protists will eat the virus, wouldn't it cause harm to them?
To know the answer to this question, you need to understand the life habits of the virus.
Liang Yantao said that viruses are a type of life form that strictly relies on host cells to obligately parasitize. Each type of virus has a very strict host range, and very few viruses can infect different organisms across different species.
In the ocean, there are tens of millions of viruses per milliliter of seawater, and there may be hundreds of thousands of types of these viruses.
However, current research shows that most of these viruses only infect bacteria and microalgae, and the number of viruses that infect protists in the ocean may be far lower than those that infect bacteria and microalgae.
"Therefore, although these types of protists may eat a lot of virus particles, most of these viruses are not viruses that infect such protists, so they will not cause harm to these virus-eating protists." Liang Yantao said.
It's not just that the food chain is completed
This is an exciting discovery.
"Viruses are rich in phosphorus and nitrogen, which may add some important nutrients to the diet of dermatoglyphids and conglomerates." Julia Brown, a bioinformatician at Bigelow Marine Science Laboratory in the United States, pointed out that since viruses are more than just Destroying other creatures will also be destroyed by other creatures, so the missing node in the food chain can now be made up.
But is the significance of this discovery really just to complement the food chain?
Liang Yantao believes that the discovery of the phenomenon of predation of viruses and protists that can prey on viruses has enabled people to have a new understanding of viruses re-entering relatively high-trophic protists and even the classic "algae-protista-fish food chain". A new study named the new pathway of predation of viruses by protozoa as viral link, which is different from the previous general understanding of the ecological role of viruses (Viral shunt).
Liang Yantao said that the role of viruses in the marine biogeochemical cycle was mainly through the lysis of bacteria and microalgae, releasing dissolved organic and inorganic substances into seawater, and these dissolved organic and inorganic substances can be reused by bacteria and algae to form A micro-food loop, thereby reducing the transmission of organic nutrients to the classic food chain.
And this new understanding of Viral link can not only enhance people’s understanding of the complex interactions of microorganisms and micro-food loops in the ocean, but also enable people to have a new understanding of the cycle of carbon, nitrogen, phosphorus, sulfur and other elements in the ocean. .
Microorganisms in the ocean significantly affect the ocean's carbon, nitrogen, phosphorus, sulfur and other elements and energy cycles, which are not only important for maintaining the health of the ecosystem, but also have an impact on global climate change through the role of ocean carbon sinks.
As the research team said, this new result is not the end.
Knowing that there are protists that can feed on viruses can provide people with "a new direction for thinking."
However, this is only a starting point for new research directions. To clarify the role of viruses in marine ecology still requires a lot of research by scientists.
But what is certain is that even viruses that “infect everything” will become a dinner for small single-celled organisms. In the dynamic balance of nature, no one can become a fish that slips through the net.