Identification of a novel subfamily of bacterial AAT-fold basic amino acid decarboxylases and functional characterization of its first representative:Pseudomonas aeruginosaLdcA

SummaryPolyamines are small amino-acid derived polycations capable of binding negatively charged macromolecules. Bacterial polyamines are structurally and functionally diverse, and are mainly produced biosynthetically by PLP-dependent amino acid decarboxylases referred to as LAOdcs (Lysine-Arginine-Ornithine decarboxylases). In a phylogenetically limited group of bacteria, LAOdcs are also induced in response to acid stress. Here, we performed an exhaustive phylogenetic analysis of the AAT-fold LAOdcs which showcased the ancestral nature of their short forms inCyanobacteriaandFirmicutes,and emergence of distinct subfamilies of long LAOdcs inProteobacteria.We identified a novel subfamily of lysine decarboxylases, LdcA, ancestral inBetaproteobacteriaandPseudomortadaceae {Gammaproteobacteria).We analyzed the expression of LdcA fromPseudomonas aeruginosa,and uncovered its role, intimately linked to cadaverine production, in promoting growth and reducing persistence of this multidrug resistant human pathogen during carbenicillin treatment. Finally, we documented a certain redundancy in the function of the three main polyamines - cadaverine, putrescine and spermidine - inP. aeruginosaby demonstrating the link between their intracellular level, as well as the capacity of putrescine and spermidine to complement the growth phenotype of theIdcAmutant.