Deletion of peptidyl-tRNA hydrolase reshapes translational homeostasis and envelope-associated stress responses in Acinetobacter baumannii

Acinetobacter baumannii is a critical multidrug-resistant pathogen responsible for severe nosocomial infections worldwide. Maintenance of translational quality control is essential for bacterial fitness under stress conditions. Peptidyl-tRNA hydrolase (Pth) rescues stalled ribosomes by hydrolyzing peptidyl-tRNA, thereby sustaining translational equilibrium. Here, we investigated the role of Pth in A. baumannii ATCC17978 through construction of a markerless ΔAbPth mutant and a complemented strain. Deletion of AbPth did not significantly affect bacterial growth under standard in vitro conditions; however, it resulted in reduced biofilm formation, altered surface morphology, impaired twitching motility, and selective extensive remodeling of proteins associated with translational quality control, envelope-associated pathways, metabolic regulation, and stress adaptation. Together, these findings suggest that AbPth is not essential for basal growth but functions as a regulator of translational modulation of stress tolerance. Antimicrobial susceptibility profiles showed only minor changes within one dilution step and did not indicate acquisition of a resistance phenotype. Label-free quantitative proteomics revealed homeostasis that coordinates downstream envelope and stress-responsive networks. Targeting translational quality-control components may therefore represent a strategy to modulate bacterial stress resilience without imposing strong bactericidal pressure.