CRISPR Detection and Protospacer Prediction in Streptococcus thermophilus
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Abstract:
The spacers in clustered regularly interspaced short palindromic repeats (CRISPR) loci can provide specific immunity to invasive elements that carry the same or a similar sequence. In the present study, the protospacers of three S. thermophilus strains were predicted to provide a foundation for exploring the phage resistance mechanism. The CRISPR sequences of three S. thermophilus strains were determined, the activity of CRISPR loci in several S. thermophilus strains was predicted, and a phylogenetic tree for repeated sequences was constructed. In addition, repeat or spacer homology was analyzed. The results showed that the tested bacterium S0 contained three CRISPR loci, S4 only had one CRISPR locus, and strain 79 had four CRISPR loci. We hypothesized that the highest and lowest activities would be observed in CRISPR1 and CRISPR2, respectively. The repeated sequences and corresponding repeated sequences in the standard strain were highly conserved, and different CRISPR spacer sequences were highly dynamic in terms of content and number. Most original spacer sequences were derived from bacteriophages, whereas a few were derived from plasmid or chromosomal sequences. The CRISPR sequence of strain 79 was highly consistent with the four CRISPR sequences of S. thermophilus MN-BM-A02 and S. thermophilus ASCC 1275, suggesting that the strains are highly homologous. The results suggest that the spacer sequences were acquired from invasion of the host by the bacteriophage and other exogenous genetic elements.
