January 18, 2021

444: Strange Sequence Stops Cell Subjugation

10 minutes

This episode: An interesting bacterial genetic element protects against viruses in a unique way!

Download Episode (7.1 MB, 10.3 minutes) Show notes: Microbe of the episode: Mongoose associated gemykibivirus 1

News item Takeaways Even single-celled, microscopic organisms such as bacteria have to deal with deadly viruses infecting them. And while they don't have an immune system with antibodies and macrophages like we do, they still have defenses against infection, mostly based on sensing and destroying viral genomes. Restriction enzymes cut viral genomes at specific places, and CRISPR/Cas targets and destroys specific viral sequences. Knowing this, when microbiologists contemplate a strange genetic element of unknown function in bacteria, it's worth considering that it may be relevant to defense against phages. The strange element in this case is retrons: a special reverse transcriptase enzyme takes a short non-coding RNA transcript and transcribes it into DNA, then links the RNA and DNA sequences together. These retrons are found in a variety of forms in a variety of microbes, and their function has been unknown up till now. In this study, one specific retron was found to defend bacteria against a number of phages. By comparing viruses, they discovered that this retron functions by sensing viruses' attempts to defeat another bacterial defense, a sort of second level of defenses. How common such a system is, what variants may exist, and how we may be able to use it for research or biotech purposes remain to be determined. Journal Paper: >Millman A, Bernheim A, Stokar-Avihail A, Fedorenko T, Voichek M, Leavitt A, Oppenheimer-Shaanan Y, Sorek R. 2020. Bacterial Retrons Function In Anti-Phage Defense. Cell 183:1551-1561.e12.