CRISPR-Cas systems constitute adaptive immune systems for antiviral defense in bacteria. We investigated the occurrence and diversity of CRISPR-Cas systems in 48 Bifidobacterium genomes to gain insights into the diversity and co-evolution of CRISPR-Cas systems within the genus and investigate CRISPR spacer content. We identified the elements necessary for the successful targeting and inference of foreign DNA in select Type II CRISPR-Cas systems, including the tracrRNA and target PAM sequence. Bifidobacterium species have a very high frequency of CRISPR-Cas occurrence (77%, 37 of 48). We found that many Bifidobacterium species have unusually large and diverse CRISPR-Cas systems that contain spacer sequences showing homology to foreign genetic elements like prophages. A large number of CRISPR spacers in bifidobacteria show perfect homology to prophage sequences harbored in the chromosomes of other species of Bifidobacterium, including some spacers that self-target the chromosome. A correlation was observed between strains that lacked CRISPR-Cas systems and the number of times prophages in that chromosome were targeted by other CRISPR spacers. The presence of prophage-targeting CRISPR spacers and prophage content may shed light on evolutionary processes and strain divergence. Finally, elements of Type II CRISPR-Cas systems, including the tracrRNA and crRNAs, set the stage for the development of genome editing and genetic engineering tools.
Occurrence and diversity of CRISPR-Cas systems in the genus Bifidobacterium / Briner, Ae; Lugli, Ga; Milani, C; Duranti, S; Turroni, F; Gueimonde, M; Margolles, A; van Sinderen, D; Ventura, M; Barrangou, R. - In: PLOS ONE. - ISSN 1932-6203. - 31:(2015), pp. 13366-13381. [10.1371/journal.pone.0133661]
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