Table 1.
Taxonomic distribution of three CRISPR-Cas system types
| Taxonomic group | Genomes analyzed | Genomes containing cas1 | Proportion of genomes containing cas1 | Genomes containing a type I system (cas7 and cas3) | Genomes containing a type II system (cas9) | Genomes containing a type III system (cas10) |
|---|---|---|---|---|---|---|
| Archaea | ||||||
| Crenarchaeota | 17 | 15 | 0.88 | 15 | 0 | 16 |
| Euryarchaeota | 47 | 37 | 0.79 | 33 | 0 | 23 |
| All Archaea | 67 | 54 | 0.81 | 50 | 0 | 40 |
| Bacteria | ||||||
| Actinobacteria | 72 | 26 | 0.36 | 28 | 15 | 8 |
| Aquificae | 7 | 5 | 0.71 | 7 | 1 | 4 |
| Bacteroidetes-Chlorobi group | 32 | 16 | 0.50 | 14 | 2 | 6 |
| Chlamydiae-Verrucomicrobia group | 10 | 2 | 0.20 | 0 | 1 | 1 |
| Chloroflexi | 10 | 9 | 0.90 | 9 | 2 | 7 |
| Cyanobacteria | 14 | 7 | 0.50 | 7 | 1 | 7 |
| Firmicutes | 126 | 56 | 0.44 | 40 | 17 | 23 |
| Proteobacteria | 318 | 107 | 0.34 | 117 | 20 | 22 |
| Spirochaetes | 13 | 3 | 0.23 | 2 | 1 | 0 |
| Thermotogae | 11 | 10 | 0.91 | 10 | 0 | 9 |
| All Bacteria | 639 | 256 | 0.40 | 245 | 65 | 99 |
cas, CRISPR-associated protein gene; CRISPR, clustered regularly interspaced short palindromic repeats.