Control of a programmed cell death pathway in Pseudomonas aeruginosa by an antiterminator

Abstract

In Pseudomonas aeruginosa the alp system encodes a programmed cell death pathway that is switched on in a subset of cells in response to DNA damage and is linked to the virulence of the organism. 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 target locus, by recognizing specific DNA sites within the promoter, then binding RNA polymerase directly and allowing it to bypass intrinsic terminators positioned downstream. AlpA thus functions in a mechanistically unusual manner to control the expression of virulence genes in this opportunistic pathogen.

ECF Sigma Factor HxuI Is Critical for In Vivo Fitness of Pseudomonas aeruginosa during Infection

“…4A , the growth inhibition zone of the Δ hxuI /pAK1900 -hxuI strain was larger than that of the wt and the Δ hxuI mutant, indicating higher intraspecies competitiveness that might be mediated by pyocin production. In addition, two sets of cell lysis genes, PA0807 ( ampDh3 )-PA0808 (immunity of AmpDh3) and alpDE ( 27 ), were upregulated at average rates of ∼2.7-fold and ∼2.1-fold, respectively, in the HxuI overexpressor ( Table 1 ). AmpDh3, a cell wall amidase, is thought to be delivered by the type VI secretion system locus II (H2-T6SS) to bacterial competitors and degrade the cell wall peptidoglycan of prey, thereby providing a growth advantage for P. aeruginosa ( 28 ).…”

SOS-Independent Pyocin Production in P. aeruginosa Is Induced by XerC Recombinase Deficiency

“…The AlpBCDE proteins, which include phage holin-like enzymes that can cause cell lysis ( 28 ), are strong candidates, as alpB was upregulated approximately 6-fold in our Δ 69700 transcriptomic data. Activation by PrtN of the alpBCDE cluster, typically activated by its own activator, AlpA ( 28 , 46 ), would be particularly interesting, with such activator cross talk perhaps serving as a fail-safe to ensure cell lysis when pyocins are expressed. Another possibility is that the absence of XerC may independently induce the Alp system, in accord with our observation of occasional cell lysis without strong pyocin expression ( Fig.…”

YgfB increases β-lactam resistance inPseudomonas aeruginosaby counteracting AlpA-mediatedampDh3expression

“…In addition, they predicted two terminator regions starting at 26 bp downstream of the ABE and at bp -178 to -137 upstream of the ampDh3 CDS. Among the two, the terminator region in close proximity to the ABE has only a minor impact on transcription 17 . In line with this, the terminator prediction tool ARNold 20 suggests one terminator region between positions -178 to -137, corresponding to the second terminator region predicted by Peña et al 17 .…”

“…Since it was shown that AlpA specifically upregulates the expression of both the alpBCDE cluster and ampDh3 , we speculated that YgfB could be a negative regulator of AlpA-mediated transcription 16, 17 . Based on the amidase function of AmpDh3 we hypothesized that ygfB deletion could increase the AmpDh3 levels, thereby leading to a reduction in the levels of anhMurNAc-peptides.…”

“…The activation of the self-lysis pathway can occur in a subset of cells in response to DNA damage, is lethal to the individual cells in which it occurs and might be required to enhance pathogenicity during lung infection 16 . Positive regulation of the expression of both the alpBCDE and ampDh3 cluster can be induced by ciprofloxacinmediated DNA damage 16,17 Since it was shown that AlpA specifically upregulates the expression of both the alpBCDE cluster and ampDh3, we speculated that YgfB could be a negative regulator of AlpA-mediated transcription 16,17 . Based on the amidase function of AmpDh3 we hypothesized that ygfB deletion could increase the AmpDh3 levels, thereby leading to a reduction in the levels of anhMurNAc-peptides.…”