Lipopolysaccharide of Klebsiella pneumoniae attenuates immunity of Caenorhabditis elegans and evades by altering its supramolecular structure

Abstract

Given the prominence of lipopolysaccharide (LPS) in the pathogenesis of Gram-negative bacteria, investigations at the molecular level in in vivo conditions are in dire need to understand its role in provoking infection. Therefore, the current study was intentionally focused on LPS of Klebsiella pneumoniae to shed more light on its role in pathogenesis using an in vivo model system, Caenorhabditis elegans. In the killing assay, LPS showed a dose-dependent mortality in C. elegans. The gene expression analysis in wild-type (N2), sek-1, pmk-1 and tol-1 mutants unveiled that K. pneumoniae-LPS targeted the p38 MAPK pathway. In unison with this, the immunoblotting analysis further confirmed the requirement of a toll-dependent p38 MAPK pathway in nematode defense against K. pneumoniae-LPS. The MALDI-TOF analysis signified that K. pneumoniae escapes from the host defense by shuttering the rapid and prolonged immune activation by modifying its lipid A structure from the hexa-acylated (potent antagonist) to hepta-acylated form (weak antagonist). In addition, the increased number of acyl chain in fatty acids and the presence of palmitate, 4-aminoarabinose along with hepta-acylated lipid A (12 and 24 h) augmented the bacterial resistances against immune defense, which further supported the survival as well as multiplication of pathogen inside the host. Furthermore, the data on FT-IR and XRD unveiled that K. pneumoniae attaches to the host by establishing a strong hydrogen bond and thereby modifying its supramolecular structure of LPS from multilamellar (biologically non-active) to cubic/hexagonal (active), to evade the immune defense of the host and cause fatal infection.