Dual Role for Pld1 in <i>Klebsiella pneumoniae</i> Virulence: Transcriptomics and Proteomics Provide Insights into Direct and Indirect Effects

<i>Klebsiella pneumoniae</i> is an opportunistic pathogen frequently found in healthcare settings, exhibiting resistance to carbapenems and third-generation cephalosporins. Hypervirulent community-acquired strains are also emerging. According to the World Health Organization (WHO), it is the top priority for developing new treatment strategies. A putative phospholipase D (PLD1) was linked to <i>K. pneumoniae</i> virulence, as a mutant strain is avirulent in a mouse model. However, the PLD1 function remains unclear. In the current study, no interaction between PLD1 and lipids was detected in a fat-blot. Lipidomic profile was not altered between strains or infected cells. To shed light on the role of PLD1, we compared the gene expression profile of a wild-type x <i>pld1</i> mutant and found 330 modulated genes. Noteworthy, capsular polysaccharide genes were increased in the wild-type, while the mutant expressed higher levels of fimbriae, conjugation systems, and stress-protection proteins. Electron microscopy confirmed a loose capsule in the mutant, which also showed an enhanced adhesion to epithelial cells. A pulldown experiment using PLD1 as bait identified 48 macrophage proteins as putative ligands, including ribosomal, RNA-related, small GTPases, and cytoskeleton-related proteins. It suggests that PLD1 may modulate host cell complexes, favoring the infection. These findings provide novel clues about PLD1's role in virulence, guiding further investigations.