New York: Scientists have found the first compelling evidence that two groups of ecologically important marine microorganisms could be eating viruses -- catching their "prey" and engulfing them, an advance that may lead to a better understanding of the flow of organic matter in the oceans.
The findings, published in the journal Frontiers in Microbiology, go against the currently predominant views of the role of both viruses and these groups of single-celled organisms called protists in the marine food webs.
"Our data show that many protist cells contain DNA of a wide variety of non-infectious viruses but not bacteria, strong evidence that they are feeding on viruses rather than on bacteria," said study corresponding author Ramunas Stepanauskas, Director of the Single Cell Genomics Center at Bigelow Laboratory for Ocean Sciences in the US.
The scientists explained that the predominant model of the role of viruses in the marine ecosystem is that of the "viral shunt," where microbes infected with viruses lose a substantial fraction of their chemicals back to the pool of dissolved organic matter.
However, the current study noted that the viral shunt could be complemented by a link in the marine microbial food web which may constitute a "sink of viral particles in the ocean."
According to the researchers, this finding "has implications for the flow of carbon through the microbial food web."
In the study, Stepanauskas and his colleagues sampled surface seawater from the Northwestern Atlantic in the Gulf of Maine in the US in July 2009, and the Mediterranean off Catalonia, Spain in January and July 2016.
They used modern single-cell genomics tools to sequence the total DNA from 1,698 individual protists in the water, and found evidence of protists with or without associated DNA.
The researchers explained that the associated DNA could be from symbiotic organisms, ingested prey, or viruses or bacteria sticking to the protists' exterior.
While the technique is very sensitive, the scientists said it doesn't directly show the type of relationship between a protist and its associates.
The scientists found a range of protists including groups called alveolates, stramenopiles, chlorophytes, cercozoans, picozoans, and choanozoans.
They said 19 per cent of the genome from the single cell organisms taken from the Gulf of Maine and 48 per cent of those from the Mediterranean were associated with bacterial DNA, suggesting that these protists had eaten bacteria.
But they added that viral sequences were more common, making up 51 per cent of the protists' genome from the Gulf of Maine and 35 per cent of those from the Mediterranean, with a frequency of one to 52 virus types per protist.
According to the researchers, most of these were from viruses known to infect bacteria -- presumably representing parasites of the protists' bacterial prey.
But they said choanozoans and picozoans, which only occurred in the Gulf of Maine sample, were different since these groups, neither of which have chloroplasts, are poorly known.
The scientists noted that the choanozoans are of great evolutionary interest as the closest living relatives of animals and fungi.
The tiny single-celled organisms were first discovered twenty years ago, and until now, their food sources were a puzzle, as their feeding apparatus is too small for bacteria, but ample for viruses, the researchers said.
In the current research, they found that every single one of the choanozoan and picozoan genomes were associated with viral sequences from bacteria-eating viruses called phages, but mostly without any bacterial DNA.
The same genome sequences were found across a great diversity of species, the study noted.
"It is very unlikely that these viruses are capable of infecting all the protists in which they were found," said Julia Brown, a co-author of the study at the Bigelow Laboratory for Ocean Sciences.
Based on these findings, the scientists concluded that choanozoans and picozoans "probably routinely eat viruses."
"Viruses are rich in phosphorus and nitrogen, and could potentially be a good supplement to a carbon-rich diet that might include cellular prey or carbon-rich marine colloids," Brown said.
The scientists believe the removal of viruses from the water may reduce the number of viruses available to infect other organisms, while also shuttling the organic carbon within virus particles higher up the food chain.
"Future research might consider whether protists that consume viruses accumulate DNA sequences from their viral prey within their own genomes, or consider how they might protect themselves from infection," Brown said.
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Batumi (Georgia), Jul 26 (PTI): Young Indian International Master Divya Deshmukh held her nerves to hold stalwart Koneru Humpy to a draw in game 1 of the FIDE Women's World Cup final, with both players having their share of opportunities to take the lead here on Saturday.
The draw with black means Humpy, the two-time World Rapid champion, holds a slight edge going in the second and final game under the classical chess rules in the two-game mini-match, and should the deadlock continue, games of shorter duration will be played to determine the winner.
Humpy employed the Queen's gambit accepted as black and it turned out to be a pretty fascinating game right out of the opening as Divya, 19, came up with a piece sacrifice early to deny the black king the right to castle.
Humpy was the first to err and, according to computers, Divya had things under control on the 14th move. However in her bid to recover the extra material, the Nagpur girl, who has secured a place in the Candidates tournament with her sterling performance here, missed a promising continuation.
What followed the exchange of all minor pieces and the ensuing queen and rook endgame gave enough counter play to both players. The game was eventually drawn after Humpy sacrificed her rook to force perpetual checks.
"The game saw an extremely sharp battle with the game ending in a draw in 41 moves. On move 7, Divya made her aggressive intentions clear by offering another pawn,
which looked like home preparation. Humpy made a practical decision of refraining from taking the pawn and a balanced position was reached by move 10 by white," said Grandmaster Pravin Thipsay, an Arjuna awardee and the first Indian to get a chess Grandmaster norm.
"However, instead of developing the undeveloped Knight, Humpy retreated the centralised Knight on move 10, giving huge positional advantage to Divya. Divya could have gained huge positional advantage on the 12th move by moving a rook. However, she chose to play for King side attack by sacrificing a piece instead.
"Humpy, too, erred at this stage and instead of moving the King to Queen side, moved it to the King side. Divya, on move 14, could have obtained a crushing attack by threatening a mate by developing her Queen. Instead she chose to exchange a pair of Bishops first, which enabled Humpy to defend her King by returning the piece," said Thipsay.
"Players thus reached a balanced Queen and two Rooks ending. Divya continued to play ambitiously and tried to attack Humpy’s King but the latter defended accurately and the game was drawn in 41 moves by perpetual check," he added.
In the play-off for the third place, Chinese players Zhongyi Tan, the former women's world champion and top seed Lei Tingjie also decided to split points out of a Queen’s gambit declined game.
The opening raised visions of a close contest between the two but having been knocked out of title race in the previous round, none of them wanted to take any huge risk. It was still a middle game when the players shook hands.
With the top two positions sealed for the Indians, the berth to the next Candidates is also assigned, while the player finishing third will also get an entry to the premier event scheduled for 2026.
Results: Divya Deshmukh (Ind) drew with Koneru Humpy (Ind); Zhongyi Tan (Chn) drew with Tingjie Lei (Chn).