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

Abstract

With the growing threat of drug-resistant Acinetobacter 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., dacC and dacD in A. baumannii. Surprisingly, the deletion of dacC resulted in a reduced growth rate, loss of rod-shaped morphology, reduction in biofilm-forming ability, and enhanced susceptibility towards {beta}-lactams, whereas, the deletion of dacD had no such effect. Interestingly, ectopic expression of dacC restored the lost phenotypes. The double deletion mutant in which both dacC and dacD were absent showed properties similar to the dacC single knockout. On the other hand, cell-shape reverting efficiency in septuple PBP deleted E. coli and in vitro enzyme kinetics assessments reveal that dacD is a stronger DD-CPase as compared to dacC. The expression of dacC was in the log phase whereas dacD expression takes place in the stationary phase. In summary, we conclude that dacC encodes a dual enzyme, possessing activities of DD-CPase and {beta}-lactamase, which significantly affects the physiology of A. baumannii in various ways whereas dacD encodes 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 O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=150 SRC="FIGDIR/small/603720v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@18820c9org.highwire.dtl.DTLVardef@208baeorg.highwire.dtl.DTLVardef@b2673eorg.highwire.dtl.DTLVardef@983aae_HPS_FORMAT_FIGEXP M_FIG C_FIG