Differential requirements for processing and transport of short-chain versus long-chain O-acylcarnitines in Pseudomonas aeruginosa

Abstract

The opportunistic pathogen Pseudomonas aeruginosa can metabolize carnitine and O-acylcarnitines, which are abundant in host muscle and other tissues. Acylcarnitines are metabolized to carnitine and a fatty acid. The liberated carnitine and its catabolic product, glycine betaine, can be used as osmoprotectants, to induce the secreted phospholipase C PlcH, and as sole carbon, nitrogen and energy sources. P. aeruginosa is incapable of de novo synthesis of carnitine and acylcarnitines, therefore they must be imported from an exogenous source. In this study, we present the first characterization of bacterial acylcarnitine transport. Short-chain acylcarnitines are imported by the ABC transporter CaiX-CbcWV. Medium- and long-chain acylcarnitines (MCACs and LCACs) are hydrolysed extracytoplasmically and the free carnitine is transported primarily through CaiX-CbcWV. These findings suggest that the periplasmic protein CaiX has a binding pocket that permits short acyl chains on its carnitine ligand and that there are one or more secreted hydrolases that cleave MCACs and LCACs. To identify the secreted hydrolase(s), we used a saturating genetic screen and transcriptomics followed by phenotypic analyses, but neither led to identification of a contributing hydrolase, supporting but not conclusively demonstrating redundancy for this activity.

Pseudomonas aeruginosainfection increases palmitoyl carnitine release by host-derived extracellular vesicles

“…PA has been shown to hydrolyze acyl-carnitines such as PAMC into carnitine and a free fatty acid. 29 Carnitine has also been shown to protect PA against osmotic stress, induce secretion of the virulence factor phospholipase C, and provide carbon and nitrogen as a source of nutrition. 30,31 However, PA can neither synthesize carnitines nor acyl-carnitines and it must acquire them from the environment.…”

“…30,31 However, PA can neither synthesize carnitines nor acyl-carnitines and it must acquire them from the environment. 29 Thus, the upregulation of PAMC in corneal epithelial cell-derived EVs may function as a protective mechanism to prevent invasive PA from scavenging carnitine within infected epithelial cells. Further research is needed to investigate this finding.…”