Control of a programmed cell death pathway in Pseudomonas aeruginosa by a ppGpp-responsive antiterminator [RNAtag-seq]

In the opportunistic pathogen Pseudomonas aeruginosa the alp system encodes a programmed cell death (PCD) pathway that is switched on in a subset of cells in response to DNA damage. Here we show that the central regulator of this pathway, AlpA, exerts its effects by acting as an antiterminator rather than a transcription activator. In particular, we present evidence that AlpA positively regulates the alpBCDE cell lysis genes, as well as genes in a second newly identified operon, by recognizing specific DNA sites within the promoter, then binding RNA polymerase directly and allowing it to bypass intrinsic terminators positioned downstream. We further show that the activity of AlpA is potentiated by the alarmone ppGpp, which is produced by the cell in response to stress. Through its responsiveness to ppGpp, AlpA can integrate environmental cues into the decision to execute a PCD pathway that is linked to the virulence of the organism. Overall design: Comparison of transcripts between wild-type PAO1 and PAO1 lacking alpA in the presence of ciprofloxacin