Table 3. Summary of clostridial Type I-B CRISPR-Cas loci analyzed to date.

Species	Number of spacers (total)a	PAM sequencesb	PAMb	Reference
C. autoethanogenum DSM 10061	22, 43, 33 (98)	5′-TAA-3′ 5′-TAA-3′ 5′-CAA-3′ 5′-GAA-3′	5′-NAA-3′	This study7
C. difficile 630/R20291	1, 2, 1, 1, 4, 2, 4, 3, 2, 14, 11, 4, 5, 4, 14, 9, 26, 9 (116)	5′-CCA-3′ 5′-CCT-3′	5′-CCW-3′c	62,7
C. pasteurianum ATCC 6013	37, 8 (45)	5′-TCA-3′ 5′-TTG-3′ 5′-TCT-3′	NDd	This study7
C. tetani 12124569	22, 3, 4, 2, 4, 5, 10, 3 (53)	5′-TAA-3′ 5′-TTA-3′ 5′-TCA-3′	5′-TNA-3′	This study7
C. thermocellum ATCC 27405	51, 96, 169, 78, 42 (436)	5′-TCA-3′ 5′-TCA-3′ 5′-ACA-3′	5′-NCA-3′	This study7

^aSpacers corresponding to Type I-B CRISPR-Cas loci analyzed in this study are bolded.

^b3 nt PAM and PAM sequences are shown. Experimentally-verified motifs are bolded.

^cW = weak (A or T).

^dND = not determined due to highly varied PAM sequences.