CRISPR-Cas Adaptive Immunity

Discovery that CRISPR loci function as a heritable, sequence-specific adaptive immune system in bacteria: spacers derived from phage/plasmid DNA are stored between repeats and used, via Cas proteins, to recognize and destroy matching invaders on reinfection. Barrangou, Fremaux, Deveau, Richards, Boyaval, Moineau, Romero & Horvath (Science 315, 1709-1712, 2007, published online 2007-03-22) provided the first direct experimental demonstration -- in the dairy-starter bacterium Streptococcus thermophilus at Danisco (an industrial yogurt-culture context, not academic curiosity) -- that adding a new phage-derived spacer confers resistance to that phage and removing it abolishes resistance. Built on Mojica et al.'s 2005 hypothesis (J. Mol. Evol. 60, 174-182, OpenAlex W1990487336) that CRISPR spacers derive from foreign genetic elements, and on the repeats themselves, first noted in 1987 (Ishino et al.). Distinct from the 2012 programmable Cas9 genome-editing tool (see the linked node) -- this node is the natural mechanism's discovery, not its later repurposing.