In eubacteria ppGpp (guanosine 3'-diphosphate 5'-diphosphate) is a mediator of the stringent response which coordinates a variety of cellular activities in response to changes in nutritional abundance. This enzyme catalyzes the formation of pppGpp which is then hydrolyzed to form ppGpp. The second messengers ppGpp and c-di-GMP together control biofilm formation in response to translational stress; ppGpp represses biofilm formation while c-di-GMP induces it. ppGpp activates transcription of CsrA-antagonistic small RNAs CsrB and CsrC, which down-regulate CsrA's action on translation during the stringent response (PubMed:21488981). ATP + GTP = AMP + guanosine 3'-diphosphate 5'-triphosphate Purine metabolism; ppGpp biosynthesis; ppGpp from GTP: step 1/2. A slight increase in biofilm formation in a csrA-disrupted background; when combined with a spoT disruption (a ppGpp0 mutant) there is a very large increase in biofilm formation (PubMed:19460094). The ppGpp0 mutant makes decreased levels of CsrA and its inhibitory small RNAs (sRNA) CsrB and CsrC (PubMed:21488981). Deletion of relA alone decreases persister cell formation in a hipA7 mutant; the double relA/spoT deletion obviates persister cell formation (PubMed:14622409, PubMed:26051177). Belongs to the RelA/SpoT family.