Stolen genes
Scientists have found common DNA in killer viruses and black widow
Geneticists unexpectedly discovered common features between bacteriophage viruses that kill microbes and black widow spiders, which indicates an unusual relationship between killer viruses, their "colleagues"-spiders and invertebrate parasites, according to an article published in the journal Nature Communications (Bordenstein & Bordenstein, Eukaryotic association module in phage WO genomes from Wolbachia).
Diseases and infections are not something that only humans and other multicellular creatures suffer from - there has been a continuous war for survival between bacteria and viruses for several hundred million years. Traces of this war can be found everywhere – for example, every milliliter of seawater contains up to a billion "combat viruses" – bacteriophages, and about 70% of marine microorganisms are infected with them.
Over billions of years of evolution, viruses have learned to bypass the attention of microbial defense systems, and the latter have acquired a kind of genetic "antivirus", the CRISPR–Cas9 system, which finds traces of viral DNA in the genome of a microbe and forces it to commit suicide to protect neighboring bacteria. In addition, bacteria have learned to hide inside the cells of other living beings, where viruses are not so easy to get into.
Sarah and Seth Bordenstein from Vanderbilt University in Nashville (USA) have uncovered an extremely unusual turn of this biological "nanowar" and have so far discovered the first example of a violation of the main law of life of viruses by studying the genomes of two "combatants" of this conflict – the parasite bacteria wolbachia, infecting the cells of spiders and insects, and its main enemy, bacteriophage WO.
Having studied the genomes of four strains of this bacteriophage, geneticists noticed something amazing – their genetic code, consisting of about 65 thousand "letters"-nucleotides, contained a fairly large piece, which in its structure was similar not to the DNA or RNA of viruses or microbes, but to the genes of multicellular creatures. The length of this section was so large that its addition to the genome of the virus actually doubled its size.
After studying their structure, scientists were surprised to find that these genes are almost complete copies of fragments of DNA of spiders and insects. They contained instructions for the assembly of latrotoxin, black widow venom, other arthropod toxins, ant genes associated with the transport of proteins through cell membranes, as well as DNA sections that help to avoid the attention of the immune system. This is the first time scientists have encountered such behavior of viruses, since it was previously believed that bacteriophages and other viruses were "aimed" at infecting only one kingdom of living beings.
Where could these genes have come from in the virus? Scientists believe that the bacteriophage "borrowed" from the organisms of those insects and arachnids into whose cells the wolbachia learned to penetrate during its evolution. The genes of spiders and ants, according to scientists, help the virus to freely enter their cells, find bacteria there, infect and destroy them. This helps the virus to multiply, and their "accomplices"-invertebrates – to get rid of the parasite.
Such "stealing" of genes is not unusual for the natural world. Scientists call this phenomenon horizontal gene transfer. Previously, it was believed that interspecific gene exchange or horizontal transfer occurs mainly among bacteria and other unicellular organisms. However, later the genes of parasitic bacteria and even plants were found in the DNA of some insects and invertebrates.
In particular, in February 2015, biologists found out that sea slugs Elysia chlorotica stole a number of genes from algae that help them steal chloroplasts from the cells of plants they eat and use them for photosynthesis. Such a "theft" is very unusual, since previously scientists did not even think that plant genes could work inside animal cells. Now they include viruses that have learned to steal genes from invertebrates.
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12.10.2016