A Unique Type V CRISPR-Cas System Encoded by a Group of Thermus Viruses
CRISPR-Cas are widespread adaptive immune systems that protect bacteria and archaea from mobile genetic elements such as bacteriophages. Metagenomic sequencing identified CRISPR-Cas systems in phage genomes; however, their functions remain largely unknown. Here, we present Cas12r-CRISPR, a novel type V CRISPR-Cas system encoded by Lalka phages infecting thermophilic Thermus bacteria. We determined Cas12r-CRISPR PAM consensus sequence and crRNA structure and showed, that when provided with appropriate spacers and expressed in Thermus thermophilus, Cas12r-CRISPR efficiently interferes with plasmid transformation as well as infection by diverse Thermus phages. In the course of Lalka phage infection, the Cas12r-CRISPR locus is expressed with middle phage genes and its transcripts are among the most abundant phage RNAs. Notably, most Cas12r-CRISPR spacers target integrative mobile elements widespread in Thermus genomes. Both Lalka phages and targeted integrative mobile elements use host tRNA genes as attachment sites. We therefore propose that Cas12r-CRISPR participates in an inter-MGEs conflict. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=81 SRC="FIGDIR/small/719267v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@f90c35org.highwire.dtl.DTLVardef@90a063org.highwire.dtl.DTLVardef@111f936org.highwire.dtl.DTLVardef@1008132_HPS_FORMAT_FIGEXP M_FIG C_FIG