Nucleotide-signaling pathways are found in all kingdoms of
life and are utilized to coordinate a rapid response to external
stimuli. The stringent response alarmones guanosine tetra(ppGpp)
and pentaphosphate (pppGpp) control a global
response allowing cells to adapt to starvation conditions such as
amino acid depletion. One more recently discovered signaling
nucleotide is the secondary messenger cyclic diadenosine
monophosphate (c-di-AMP). Here, we demonstrate that this
signaling nucleotide is essential for the growth of Staphylococcus
aureus, and its increased production during late growth
phases indicates that c-di-AMP controls processes that are
important for the survival of cells in stationary phase. By examining
the transcriptional profile of cells with high levels of c-diAMP,
we reveal a significant overlap with a stringent response
transcription signature. Examination of the intracellular nucleotide
levels under stress conditions provides further evidence
that high levels of c-di-AMP lead to an activation of the stringent
response through a RelA/SpoT homologue (RSH) enzymedependent
increase in the (p)ppGpp levels. This activation is
shown to be indirect as c-di-AMP does not interact directly with
the RSH protein. Our data extend this interconnection further
by showing that the S. aureus c-di-AMP phosphodiesterase
enzyme GdpP is inhibited in a dose-dependent manner by
ppGpp, which itself is not a substrate for this enzyme. Altogether,
these findings add a new layer of complexity to our
understanding of nucleotide signaling in bacteria as they highlight
intricate interconnections between different nucleotidesignaling
networks.