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CRISPR–Cas systems in bacteria and archaea have multifaceted evolutionary relationships with mobile genetic elements (MGEs), including viruses, plasmids and transposons. CRISPR–Cas systems or their components have also been recruited by MGEs on many independent occasions. In this Analysis article, Koonin and colleagues investigate and substantially expand the range of CRISPR–Cas components carried by MGEs.
In this Analysis article, Flemming and Wuertz calculate the total number of bacteria and archaea on Earth and estimate the fraction that lives in biofilms. They propose that biofilms are the most prominent and influential type of microbial life.
