Huge viruses that kill bacteria hide in ecosystems around the world, from hot springs to lakes and freshwater rivers. Now, a team of researchers has discovered some of these so-called bacteriophages that are so large and so complex that they blur the line between living and not living, according to the new findings.
Bacteriophages, or “phages” for short, are virus that specifically infect bacteria. Phages and other viruses are not considered living organisms because they cannot perform biological processes without the help and cellular machines of another organism.
This does not mean that they are harmless: phages are the main drivers of ecosystem change because they prey on populations of bacteria, alter their metabolism, spread antibiotic resistance and transport compounds that cause disease in animals and humans, according to the researchers in a new study, published in the journal on February 12 Nature.
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To find out more about these sneaky invaders, the researchers searched in DNA a database they created from samples collected by them and their colleagues in nearly 30 different environments around the world, ranging from the bowels of Alaskan people and moose to a South African bioreactor and a Tibetan thermal spring, according to a statement.
From that DNA, they discovered 351 huge phages that had genomes four or more times larger than the average phage genome. Among them was the largest phage found to date with a genome of 735,000 base pairs – the nucleotide pairs that make up the rungs of the ladder structure of the DNA molecule – or nearly 15 times larger than the average phage. (The human genome contains around 3 billion base pairs.)
These phages are “hybrids between what we think of as traditional viruses and traditional living organisms”, such as bacteria and archaea, senior author Jill Banfield, University of California, Berkeley, professor of Earth and planetary sciences and environmental sciences, politics and management , stated in the statement. The genome of this huge phage is much larger than the genomes of many bacteria, according to the statement.
The authors found that many of the genes encoded proteins that are still unknown to us. They found that phages had a number of genes that are not typical of viruses but are typical of bacteria, according to the statement. Some of these genes are part of a system that bacteria use to fight viruses (and was later adapted by humans to modify genes, a technique called CRISPR-Cas9).
Scientists don’t know for sure, but they think that once these phages inject their DNA into bacteria, the phage’s CRISPR system strengthens the bacteria’s CRISPR system. In this way, the combined CRISPR system could help hit other phages (get rid of the competition).
In addition, they found that some of the phages had genes that encoded the proteins necessary for the functioning of the ribosomes – a cellular machine that translates genetic material into proteins (proteins are the molecules that carry out DNA instructions) . These proteins are not typically found in viruses, but are found in bacteria and archaea, according to the statement.
Some of these new phages may also use ribosomes in the bacterial host to make multiple copies of their proteins, according to the statement.
“Typically, what separates life from non-life is having ribosomes and the ability to do translation; this is one of the main distinguishing features that separate viruses and bacteria, non-life and life,” the co-host author Rohan Sachdeva, a researcher associated with UC Berkeley, said in the statement. “Some big phages have a lot of this translational machinery, so they’re blurring the line a little.”
Originally published on Live science.