Researchers have discovered that hundreds of relatively larger bacteriophages possess proteins that are used to direct their bacterial hosts. The proteins can affect the ribosomal production of proteins as well as the CRISPR bacterial immune system.
The research team (from University of California, Berkeley) has described the bacteriophages as a type of hybrid between living microbes and viral machines. This is in contrast to most conceptions of viruses, where a virus is not considered to be ‘living’ in the conventional sense. A little like a seed, a virus is closer to an object with the potential for life, only capable of replication inside the cell of a living creature, where they effectively make copies of themselves.
Bacteriophages are formed of proteins that encapsulate a DNA or RNA genome. Phages replicate within a bacterium following the injection of their genome into its cytoplasm. Bacteriophages have long been researched as alternatives to antimicrobials, based on their bacterial killing function and because bacteria cannot develop resistance to the viruses.
With the new research, the focus was on ‘large’ phages, defined as viruses with genomes four or more times bigger than the average genomes of viruses that target single-celled bacteria. In all, some 351 of these large bacteriophages have been identified.
The samples from taken from around thirty different environments, including such diverse locales as a Tibetan hot spring, oceans, hospital rooms, and pregnant women.
The biggest bacteriophage isolated, and identified through an assessment of metagenomic sequences, was found to have a genome some 735,000 base-pairs long. This makes the virus around 15 times bigger than the typical phage.
The researchers put forward the possibility that such large phages are hybrids, presenting the divide between non-living bacteriophages and living bacteria.
Aside from being of general interest, the discovery of the super-large bacteriophages holds the potential for discovering alternative tools for genome engineering. In addition, it is thought that phages are one mechanism from the spread of antimicrobial resistant genes between bacteria; that is, phages may have an indirect role in boosting antimicrobial resistance and thereby helping to facilitate human disease.
The research has been published in the journal Nature. The research paper is titled “Clades of huge phages from across Earth’s ecosystems.”
