Abstract
Clustered regularly interspaced short palindromic repeats (CRISPR) and the CRISPR-associated proteins (Cas) provide bacteria and archaea with adaptive immunity to specific DNA invaders. Mycobacterium tuberculosis encodes a type III CRISPR-Cas system that has not been experimentally explored. In this study, we found that the CRISPR-Cas systems of both M. tuberculosis and Mycobacterium bovis BCG were highly upregulated by deletion of Rv2837c (cnpB), which encodes a multifunctional protein that hydrolyzes cyclic di-AMP (c-di-AMP), cyclic di-GMP (c-di-GMP), and nanoRNAs (short oligonucleotides of 5 or fewer residues). By using genetic and biochemical approaches, we demonstrated that the CnpB-controlled transcriptional regulation of the CRISPR-Cas system is mediated by an Orn-like activity rather than by hydrolyzing the cyclic dinucleotides. Additionally, our results revealed that tuberculosis (TB) complex mycobacteria are functional in processing CRISPR RNAs (crRNAs), which are also more abundant in the ΔcnpB strain than in the parent strain. The elevated crRNA levels in the ΔcnpB strain could be partially reduced by expressing Escherichia coli orn Our findings provide new insight into transcriptional regulation of bacterial CRISPR-Cas systems.IMPORTANCE Clustered regularly interspaced short palindromic repeats (CRISPR) and the CRISPR-associated proteins (Cas) provide adaptive immunity to specific DNA invaders. M. tuberculosis encodes a type III CRISPR-Cas system that has not been experimentally explored. In this study, we first demonstrated that the CRISPR-Cas systems in tuberculosis (TB) complex mycobacteria are functional in processing CRISPR RNAs (crRNAs). We also showed that Rv2837c (CnpB) controls the expression of the CRISPR-Cas systems in TB complex mycobacteria through an oligoribonuclease (Orn)-like activity, which is very likely mediated by nanoRNA. Since little is known about regulation of CRISPR-Cas systems, our findings provide new insight into transcriptional regulation of bacterial CRISPR-Cas systems.