## 1 Introduction  
Microorganisms continuously face abrupt changes in natural ecosystems that are detrimental to life. However, they rapidly respond to such challenging conditions by activating different strategies of cell survival [1]. These responses are coordinated by signal transduction pathways usually activated by second messengers, resulting in alterations in gene expression and adjustments in cellular physiology [2, 3]. A group of second messengers is synthesized from nucleotide precursors, adopting distinctive chemical structures, and are distributed across all domains of life [2, 4]. Bacteria can produce different nucleotide-based second messengers, including the classical cyclic-adenosine-monophosphate (c-AMP), the alarmome guanosine-(penta)tetraphosphate [(ppppGpp)] and of most recent interest, cyclic-di-guanosine-monophosphate (c-di-GMP) and cyclic-diadenosine-monophosphate (c-di-AMP) [2, 4]. The latter is synthesized by diadenylate cyclases (DACs) from two ATP molecules and hydrolyzed by specific phosphodiesterase [4, 5]. All known enzymes that produce c-di-AMP share a catalytically active diadenylate cyclase (DAC) domain which is complemented by a regulatory domain. Based on this modular arrangement, five classes of DACs possessing different types of regulatory domains have been identified in bacteria: namely, DisA, CdaA, CdaS, CdaM, and CdaZ [6, 7].  
The Gram-positive bacterium _B. subtilis_ employs three different DACs (DisA, CdaA and CdaS) to synthesize c-di-AMP [8, 9]. The most conserved class of DAC is represented by CdaA [10]. In _B. subtilis_, this protein physically interacts with GlnM, an essential enzyme that catalyzes an early step in peptidoglycan biosynthesis. This interaction likely links cell wall homeostasis to CdaA activity and thus to c-di-AMP levels in the cell [10].  
A developmental DNA damage-dependent checkpoint role during the early stages of _B. subtilis_ sporulation has been attributed to DisA [11]. It has been shown that DNA lesions diminished both DisA activity and c-di-AMP levels, which results in a sporulation delay [11; 12; 13]. Most recently, we showed that ROS-promoted DNA lesions activate the checkpoint function of DisA, and together with the transcriptional repair factor Mfd, DisA was found to coordinate excision repair events for efficient _B. subtilis_ spore outgrowth [14; 15]. Therefore, CdaA and DisA seem to play a role in protecting vegetative _B. subtilis_ cells from DNA-damaging agents [16]. Interestingly, CdaS, a spore-specific DAC, does not contribute to DNA repair, but its function is required for spores to return to vegetative growth [17].  
During post-exponential growth, _B. subtilis_ activates mechanisms that promote genetic variability, which allows this bacterium to escape from growth-limiting conditions. This process has been termed stress-associated mutagenesis (SAM) and takes place in non-dividing bacteria when cells experience a non-lethal selective pressure [18; 19]. Previous results from a proteomic analysis demonstrated a relationship between nutritional stress and dysregulation in the levels of DACs and other proteins that degrade or interact with c-di-AMP, suggesting a possible role of this metabolite on _B. subtilis_ SAM [20]. In this study we investigated the role of CdaA, DisA and c-di-AMP levels in SAM and growth-associated mutagenesis (GAM). Overall, our results revealed that c-di-AMP produced by DACs CdaA and DisA is needed to prevent mutagenesis during growth; however, in non-dividing or nutrient-limiting conditions, this cyclic dinucleotide may activate programs that produce genetic diversity, which increases the likelihood of escaping growth-limiting conditions.