Role of the Streptococcus mutans CRISPR-Cas Systems in Immunity and Cell Physiology
CRISPR-Cas systems provide adaptive microbial immunity against invading viruses and plasmids. The cariogenic bacteriumStreptococcus mutansUA159 has two CRISPR-Cas systems: CRISPR1 (type II-A) and CRISPR2 (type I-C) with several spacers from both CRISPR cassettes matching sequences of phage M102 or genomic sequences of otherS. mutans. The deletion of thecasgenes of CRISPR1 (ΔC1S), CRISPR2 (ΔC2E), or both CRISPR1+2 (ΔC1SC2E) or the removal of spacers 2 and 3 (ΔCR1SP13E) inS. mutansUA159 did not affect phage sensitivity when challenged with virulent phage M102. Using plasmid transformation experiments, we demonstrated that the CRISPR1-Cas system inhibits transformation ofS. mutansby the plasmids matching the spacers 2 and 3. Functional analysis of thecasdeletion mutants revealed that in addition to a role in plasmid targeting, both CRISPR systems also contribute to the regulation of bacterial physiology inS. mutans. Compared to wild-type cells, the ΔC1S strain displayed diminished growth under cell membrane and oxidative stress, enhanced growth under low pH, and had reduced survival under heat shock and DNA-damaging conditions, whereas the ΔC2E strain exhibited increased sensitivity to heat shock. Transcriptional analysis revealed that the two-component signal transduction system VicR/K differentially modulates expression ofcasgenes within CRISPR-Cas systems, suggesting that VicR/K might coordinate the expression of two CRISPR-Cas systems. Collectively, we providein vivoevidence that the type II-A CRISPR-Cas system ofS. mutansmay be targeted to manipulate its stress response and to influence the host to control the uptake and dissemination of antibiotic resistance genes.