Natures wonders: virus that eat bacteria (Introduction)

by David Turell @, Wednesday, February 12, 2020, 21:19 (10 days ago) @ David Turell

Normally bacteriophages just infect bacteria. this giant group eats them as if they were fully alive:

"These phages—short for bacteriophages, so-called because they "eat" bacteria—are of a size and complexity considered typical of life, carry numerous genes normally found in bacteria and use these genes against their bacterial hosts.


"Among these is the largest bacteriophage discovered to date: Its genome, 735,000 base-pairs long, is nearly 15 times larger than the average phage. This largest known phage genome is much larger than the genomes of many bacteria.


"'These huge phages bridge the gap between non-living bacteriophages, on the one hand, and bacteria and Archaea. There definitely seem to be successful strategies of existence that are hybrids between what we think of as traditional viruses and traditional living organisms."

"Ironically, within the DNA that these huge phages lug around are parts of the CRISPR system that bacteria use to fight viruses. It's likely that once these phages inject their DNA into bacteria, the viral CRISPR system augments the CRISPR system of the host bacteria, probably mostly to target other viruses.


"The team identified 351 phage genomes that were more than 200 kilobases long, four times the average phage genome length of 50 kilobytes (kb). They were able to establish the exact length of 175 phage genomes; the others could be much larger than 200 kb. One of the complete genomes, 735,000 base-pairs long, is now the largest known phage genome.

"While most of the genes in these huge phages code for unknown proteins, the researchers were able to identify genes that code for proteins critical to the machinery, called the ribosome, that translates messenger RNA into protein. Such genes are not typically found in viruses, only in bacteria or archaea.

"The researchers found many genes for transfer RNAs, which carry amino acids to the ribosome to be incorporated into new proteins; genes for proteins that load and regulate tRNAs; genes for proteins that turn on translation and even pieces of the ribosome itself.

"Typically, what separates life from non-life is to have ribosomes and the ability to do translation; that is one of the major defining features that separate viruses and bacteria, non-life and life," Sachdeva said. "Some large phages have a lot of this translational machinery, so they are blurring the line a bit."

"Huge phages likely use these genes to redirect the ribosomes to make more copies of their own proteins at the expense of bacterial proteins. Some huge phages also have alternative genetic codes, the nucleic acid triplets that code for a specific amino acid, which could confuse the bacterial ribosome that decodes RNA.


"'The high-level conclusion is that phages with large genomes are , they are quite prominent across Earth's ecosystemsnot a peculiarity of one ecosystem," Banfield said. "And phages which have large genomes are related, which means that these are established lineages with a long history of large genome size. Having large genomes is one successful strategy for existence, and a strategy we know very little about.'"

Comment: Another strange part of the bush of life . It is found in many ecosystems as the bold notes, so it must be assumed they play a required role.

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