Acinetobacter baumanniiDacC influences cell shape, biofilm formation and physiological fitness by manifesting DD-carboxypeptidase, and β-lactamase dual-enzyme activities

Abstract

AbstractWith the growing threat of drug-resistantAcinetobacter baumannii, there is an urgent need to comprehensively understand the physiology of this nosocomial pathogen. As penicillin-binding proteins are attractive targets for antibacterial therapy, herein we have tried to explore the physiological roles of two putative DD-carboxypeptidases, viz.,dacCanddacDinA. baumannii. Surprisingly, the deletion ofdacCresulted in a reduced growth rate, loss of rod-shaped morphology, reduction in biofilm-forming ability, and enhanced susceptibility towards β-lactams, whereas, the deletion ofdacDhad no such effect. Interestingly, ectopic expression ofdacCrestored the lost phenotypes. The double deletion mutant in which bothdacCanddacDwere absent showed properties similar to thedacCsingle knockout. On the other hand, cell-shape reverting efficiency in septuple PBP deletedE. coliandin vitroenzyme kinetics assessments reveal thatdacDis a stronger DD-CPase as compared todacC. The expression ofdacCwas in the log phase whereasdacDexpression takes place in the stationary phase. In summary, we conclude thatdacCencodes a dual enzyme, possessing activities of DD-CPase and β-lactamase, which significantly affects the physiology ofA. baumanniiin various ways whereasdacDencodes a strong DD-CPase and plays a role in cell morphology, though it exerts negligible impact on other physiological aspects like intrinsic antibiotic resistance or biofilm formation.Graphical Abstract