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

Klebsiella pneumoniae 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 K. pneumoniae 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 pld1 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.