LIPI-4 and lmo0180 cooperatively regulate flagellar motility and virulence in Listeria monocytogenes

Abstract

Deletion of Listeria pathogenicity island 4 (LIPI-4) in Listeria monocytogenes ( L. monocytogenes ) impairs motility, disrupts flagellar assembly, and markedly upregulates the lmo0180 gene. In this study, the Δ lmo0180 single-gene deletion mutant and ΔLIPI-4/ lmo0180 double-gene deletion mutant were constructed by homologous recombination. Bacterial motility was assessed, and flagellar biogenesis was observed by transmission electron microscopy. The adhesion, invasion, intracellular proliferation, and cell-to-cell spread capacities were compared across strains. Virulence was evaluated in a mouse model, and transcript levels of major virulence factors were quantified by quantitative real-time PCR. The results showed that deletion of lmo0180 alone had no detectable effects on bacterial motility, flagellar formation, or virulence-related phenotypes. In contrast, LIPI-4 deletion enhanced biofilm formation and eliminated motility and flagellar assembly. Simultaneous deletion of LIPI-4 and lmo0180 restored bacterial motility, flaA gene expression, and partial restoration of flagellar assembly; however, the double mutant displayed significant reductions in adhesion, invasion, intracellular proliferation, and cell-to-cell spread in host cells. In vivo experiments consistently showed that mice infected with the ΔLIPI-4/ lmo0180 mutant exhibited reduced bacterial loads and tissue damage. Compared with the ΔLIPI-4 strain that exhibited elevated transcript levels of PrfA-controlled virulence genes, the ΔLIPI-4/ lmo0180 mutant exhibited downregulation of most such genes. These transcriptional changes may contribute to the attenuated virulence phenotype. Collectively, the study demonstrates that LIPI-4 and lmo0 180 interact genetically to influence flagellar motility and virulence in L. monocytogenes , a finding that provides new insights into the pathogenic mechanisms of L. monocytogenes .