A LexA-like repressor and global H-NS-like regulators enable the fine-tuning of R-tailocin expression in environmental Pseudomonas

Bacteria rely on an arsenal of weapons to challenge their opponents in highly competitive environments. To specifically counter closely related bacteria, specialized weapons with a narrow activity spectrum are deployed, particularly contractile phage tail-like particles or R-tailocins. Their production leads to the lysis of the producing cells, indicating that their expression must be carefully orchestrated so that only a small percentage of cells produce R-tailocins for the benefit of the entire population. In this study, we set out to better understand how the production of these phage tail-like weapons is regulated in environmental pseudomonads using the competitive plant root colonizer and environmental model Pseudomonas protegens CHA0. Using an RNA sequencing (RNA-seq) approach, we found that genes involved in DNA repair, particularly the SOS response program, are upregulated following exposure of the pseudomonad to the DNA-damaging agents mitomycin C and hydrogen peroxide, while genes involved in cell division and primary metabolism are downregulated. The R-tailocin and prophage gene clusters were also upregulated in response to these DNA damaging agents. By combining reverse genetics, transcriptional reporters and chromatin immunoprecipitation sequencing (ChIP-seq), we show that the R-tailocin locus-specific LexA-like regulator PrtR1 represses R-tailocin gene expression by binding directly to the promoter region of the cluster, while the histone-like nucleoid structuring (H-NS) proteins MvaT and MvaV act as master regulators that indirectly regulate R-tailocin cluster expression. Our results suggest that at least these three regulators operate in concert to ensure tight control of R-tailocin expression and cell lytic release in environmental Pseudomonas strains. Author SummaryTo face their opponents in highly competitive environments, bacteria rely on an arsenal of weapons. To specifically target closely related bacterial strains, specialized weapons with a narrow activity spectrum are produced, notably contractile phage tail-like particles such as R-tailocins. Since production of these particles leads to the lysis and death of the producing cell, their expression must be tightly regulated. Here, we set out to better understand how the expression of these phage tail-like weapons is regulated in environmental bacteria using the competitive plant root colonizer and environmental model Pseudomonas protegens CHA0. We found that following DNA-damaging stress, which activates DNA repair systems and downregulates primary metabolism, the expression of gene clusters encoding viral-like particles such as the R-tailocins is upregulated. We identified cluster-specific and global regulators that are either directly or indirectly involved in the control of R-tailocin cluster expression. Our results contribute to a better understanding of the regulatory mechanisms of viral-like particle production in environmental Pseudomonas bacteria.