In vivo synthesis of monolysocardiolipin and cardiolipin by Acinetobacter baumannii phospholipase D and effect on cationic antimicrobial peptide resistance.

Acinetobacter baumannii is an opportunistic pathogen, which has become a rising threat in healthcare facilities worldwide due to increasing antibiotic resistances and optimal adaptation to clinical environments and the human host. We reported in a former publication on the identification of three phopholipases of the phospholipase D (PLD) superfamily in A. baumannii ATCC 19606 acting in concerted manner as virulence factors in Galleria mellonella infection and lung epithelial cell invasion. This study focussed on the function of the three PLDs. A Δpld1-3 mutant was defect in biosynthesis of the phospholipids cardiolipin (CL) and monolysocardiolipin (MLCL), whereas the deletion of pld2 and pld3 abolished the production of MLCL. Complementation of the Δpld1-3 mutant with pld1 restored CL biosynthesis demonstrating that the PLD1 is implicated in CL biosynthesis. Complementation of the Δpld1-3 mutant with either pld2 or pld3 restored MLCL and CL production leading to the conclusion that PLD2 and PLD3 are implicated in CL and MLCL production. Mutant studies revealed that two catalytic motifs are essential for the PLD3-mediated biosynthesis of CL and MLCL. The Δpld1-3 mutant exhibited a decreased colistin and polymyxin B resistance indicating a role of CL in cationic antimicrobial peptides (CAMPs) resistance.