Independent and dependent life (Introduction)

by David Turell @, Sunday, August 23, 2020, 15:23 (468 days ago)

Parasites and viruses are not independent life, but some macrophages among the bacteriophages blur the lines:

"Bacterial viruses, called bacteriophages, are simple genetic machines, relying on their bacterial hosts to replicate and spread. But scientists have found hundreds of huge phages that carry a slew of bacterial proteins that the phages evidently use to more efficiently manipulate their microbial hosts. These proteins include those involved with ribosomal production of proteins and the CRISPR bacterial immune system, as if the phages are a hybrid between living microbes and viral machines.


"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.


"Altogether they identified 351 different huge phages, all with genomes four or more times larger than the average genomes of viruses that prey on single-celled bacteria.

"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.

"'It is fascinating how these phages have repurposed this system we thought of as bacterial or archaeal to use for their own benefit against their competition, to fuel warfare between these viruses,"


"'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."

Comment: Amazing. These phage have stolen a bacterial defense mechanism CRISPR from bacteria. Every type of life has its own pathogens, even bacteria that attack us. More proof of the diversity of the living and the partially living.

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