eThe opportunistic pathogen Pseudomonas aeruginosa is capable of establishing severe and persistent infections in various eukaryotic hosts. It encodes a wide array of virulence factors and employs several strategies to evade immune detection. In the present study, we screened the Harvard Medical School transposon mutant library of P. aeruginosa PA14 for bacterial factors that modulate interleukin-8 responses in A549 human airway epithelial cells. We found that in addition to the previously identified alkaline protease AprA, the elastase LasB is capable of degrading exogenous flagellin under calcium-replete conditions and prevents flagellin-mediated immune recognition. Our results indicate that the production of two proteases with anti-flagellin activity provides a failsafe mechanism for P. aeruginosa to ensure the maintenance of protease-dependent immune-modulating functions.

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Transfer RNA (tRNA) modifications impact the structure and function of tRNAs, thus affecting the efficiency and fidelity of translation. In the opportunistic pathogen Pseudomonas aeruginosa translational regulation plays an important but less defined role in adaptation to changing environments. In this study, we have explored tRNA modifications in P. aeruginosa through LC‐MS/MS approaches. Neutral loss scanning (NLS) demonstrated the potential to identify previously unknown modifications, whereas multiple reaction monitoring (MRM) was able to detect modifications with high specificity and sensitivity. In this study, the MRM‐based external calibration method allowed for quantification of the four canonical and 32 modified ribonucleosides, out of which 21 tRNA modifications were quantified in the total tRNA pool of P. aeruginosa PA14. We also purified the single tRNA isoacceptors tRNA‐ArgUCU, tRNA‐LeuCAA, and tRNA‐TrpCCA and determined their specific modification patterns, both qualitatively and quantitatively. Deeper insights into the nature and dynamics of tRNA modifications in P. aeruginosa should pave the way for further studies on post‐transcriptional gene regulation as a relatively unexplored molecular mechanism of controlling bacterial pathogenicity and mode of growth.

SAW1 , coding for Saw1, is required for single-strand annealing (SSA) DNA Double-strand Break (DSB) Repair in S. cerevisiae. Saw1 physically associates with Rad1 and Rad52 and recruits the Rad1-Rad10 endonuclease. Herein we show by fluorescence microscopy that SAW1 is similarly required for recruitment of Rad10 to sites of Synthesis-Dependent Strand Annealing (SDSA) and associates with sites of SDSA repair in a manner temporally overlapped with Rad10. The magnitude of induction of colocalized Saw1-CFP/Rad10-YFP/DSB-RFP foci in SDSA is more dramatic in S and G2 phase cells than in M phase, consistent with the known mechanism of SDSA. We observed a substantial fraction of foci in which Rad10 was localized to the repair site without Saw1, but few DSB sites that contained Saw1 without Rad10. Together these data are consistent with a model in which Saw1 recruits Rad1-Rad10 to SDSA sites, possibly even binding as a protein-protein complex, but departs the repair site in advance of Rad1-Rad10.