Number of spacer sequences and its similarities against known phage genome of CRISPR in S. mutans strains. (a) CRISPR-2 regions, widely distributed among S. mutans, in strain NN2025, UA159 and six selected strains (MT8148, LJ29, SA13, SA15, NN2207 and NN2138; see additional file 5 and 6). Blue rectangles indicate the direct repeat (DR). Orange triangles indicate spacer regions without homology to the phage M102 genome and red triangles are spacer regions corresponding to the sequence of the phage. Numbers of the spacer regions are determined by CRISPRfinder (see Methods for details). (b) Location of the spacer sequences corresponding to the M102 phage sequence (red arrowheads). The number of each arrowhead indicates the spacer number of each strain (additional file 9). The sequences of leader, spacer and repeat of CRISPR loci in the strain NN2025 and UA159 are listed in additional files 8, 9 and 10.