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    STUDIA BIOLOGIA - Issue no. 1 / 2019  
         
  Article:   CRISPR-CAS SYSTEMS IN HALOARCHAEA MORE THAN JUST ANTIVIRAL DEFENSE?.

Authors:  ISRAELA TURGEMAN-GROTT, URI NERI, MATTHEW OUELLETTE, R. THANE PAPKE, URI GOPHNA. 		 
       
         
  Abstract:  Many archaea possess spacers that match chromosomal genes of related species, including those encoding core housekeeping genes. By sequencing genomes of environmental archaea isolated from a single site, we demonstrate that inter-species spacers are common. We then showed experimentally, by mating Haloferax volcanii and Haloferax mediterranei, that spacers are indeed acquired chromosome-wide, although a preference for integrated mobile elements and nearby regions of the chromosome exists. Engineering the chromosome of one species to be targeted by the other’s CRISPR–Cas reduces gene exchange between them substantially. Thus, spacers acquired during inter-species mating could limit future gene transfer, resulting in a role for CRISPR–Cas systems in microbial speciation. More recently we have identified a virus that chronically infects one of our natural Haloferax isolates and can also integrate into its genome. Exposure to this virus elicited strong and specific spacer acquisition by the H. volcanii lab strain, that surprisingly Could not be stably infected by that virus. This raised the question why the virus'' original host that appears to have a functional CRISPR-Cas system did not acquire spacers from a virus that chronically infects it. We addressed this by an “active immunization” approach in which provirus-containing cells were exposed to mature virus particles.

Keywords: CRISPR-Cas, halophilic archaea, horizontal gene transfer, lateral gene transfer, viruses. 		 
         
     
         
         
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