Ribonuclease J-Mediated mRNA Turnover Modulates Cell Shape, Metabolism and Virulence in <i>Corynebacterium diphtheriae</i>

Controlled RNA degradation is a crucial process in bacterial cell biology for maintaining proper transcriptome homeostasis and adaptation to changing environments. mRNA turnover in many Gram-positive bacteria involves a specialized ribonuclease called RNase J (RnJ). To date, however, nothing is known about this process in the diphtheria-causative pathogen <i>Corynebacterium diphtheriae</i>, nor is known the identity of this ribonuclease in this organism. Here, we report that <i>C. diphtheriae</i> DIP1463 encodes a predicted RnJ homolog, comprised of a conserved N-terminal β-lactamase domain, followed by β-CASP and C-terminal domains. A recombinant protein encompassing the β-lactamase domain alone displays 5′-exoribonuclease activity, which is abolished by alanine-substitution of the conserved catalytic residues His¹⁸⁶ and His¹⁸⁸. Intriguingly, deletion of DIP1463/<i>rnj</i> in <i>C. diphtheriae</i> reduces bacterial growth and generates cell shape abnormality with markedly augmented cell width. Comparative RNA-seq analysis revealed that RnJ controls a large regulon encoding many factors predicted to be involved in biosynthesis, regulation, transport, and iron acquisition. One upregulated gene in the ∆<i>rnj</i> mutant is <i>ftsH</i>, coding for a membrane protease (FtsH) involved in cell division, whose overexpression in the wild-type strain also caused cell-width augmentation. Critically, the ∆<i>rnj</i> mutant is severely attenuated in virulence in a <i>Caenorhabditis elegans</i> model of infection, while the FtsH-overexpressing and toxin-less strains exhibit full virulence as the wild-type strain. Evidently, RNase J is a key ribonuclease in <i>C. diphtheriae</i> that post-transcriptionally influences the expression of numerous factors vital to corynebacterial cell physiology and virulence. Our findings have significant implications for basic biological processes and mechanisms of corynebacterial pathogenesis.