AUTHOR=Wang Gang , Liu Qian , Pei Zhangming , Wang Linlin , Tian Peijun , Liu Zhenmin , Zhao Jianxin , Zhang Hao , Chen Wei 

TITLE=The Diversity of the CRISPR-Cas System and Prophages Present in the Genome Reveals the Co-evolution of Bifidobacterium pseudocatenulatum and Phages

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.01088

DOI=10.3389/fmicb.2020.01088

ISSN=1664-302X

ABSTRACT=<p>Diverse CRISPR-Cas systems constitute an indispensable part of the bacterial adaptive immune system against viral infections. However, to escape from this immune system, bacteriophages have also evolved corresponding anti-defense measures. We investigated the diversity of CRISPR-Cas systems and the presence of prophages in the genomes of 66 <italic>Bifidobacterium pseudocatenulatum</italic> strains. Our findings revealed a high occurrence of complete CRISPR-Cas systems (62%, 41/66) in the <italic>B. pseudocatenulatum</italic> genomes. Subtypes I-C, I-U and II-A, were found to be widespread in this species. No significant association was found between the number of bacterial CRISPR spacers and its host’s age. This study on prophages within <italic>B. pseudocatenulatum</italic> genomes revealed that prophage genes related to distinct functional modules became degraded at different levels, indicating that these prophages were not likely to enter lytic cycle spontaneously. Further, the evolutionary analysis of prophages in this study revealed that they might be derived from different phage ancestors. Notably, self-targeting phenomenon within <italic>B. pseudocatenulatum</italic> and Anti-CRISPR (Acr) coding genes in prophages was observed. Overall, our results indicate that the competition between <italic>B. pseudocatenulatum</italic> and phages is a major driving factor for the genomic diversity of both partners.</p>