G C A T T A C G G C A T genes Review c-di-AMP: An Essential Molecule in the Signaling Pathways that Regulate the Viability and Virulence of Gram-Positive Bacteria Tazin Fahmi 1, Gary C. Port 2,3 and Kyu Hong Cho 1,* ID 1 Department of Biology, Indiana State University, Terre Haute, IN 47809, USA;
[email protected] 2 Department of Molecular Microbiology, Washington University School of Medicine, Saint Louis, MO 63110, USA;
[email protected] 3 Elanco Animal Health, Natural Products Fermentation, Eli Lilly and Company, Indianapolis, IN 46285, USA * Correspondence:
[email protected]; Tel.: +1-812-237-2412 Academic Editor: Helen J. Wing Received: 26 June 2017; Accepted: 31 July 2017; Published: 7 August 2017 Abstract: Signal transduction pathways enable organisms to monitor their external environment and adjust gene regulation to appropriately modify their cellular processes. Second messenger nucleotides including cyclic adenosine monophosphate (c-AMP), cyclic guanosine monophosphate (c-GMP), cyclic di-guanosine monophosphate (c-di-GMP), and cyclic di-adenosine monophosphate (c-di-AMP) play key roles in many signal transduction pathways used by prokaryotes and/or eukaryotes. Among the various second messenger nucleotides molecules, c-di-AMP was discovered recently and has since been shown to be involved in cell growth, survival, and regulation of virulence, primarily within Gram-positive bacteria. The cellular level of c-di-AMP is maintained by a family of c-di-AMP synthesizing enzymes, diadenylate cyclases (DACs), and degradation enzymes, phosphodiesterases (PDEs). Genetic manipulation of DACs and PDEs have demonstrated that alteration of c-di-AMP levels impacts both growth and virulence of microorganisms.