Abstract
In the Medicago truncatula genome about 700 genes code for nodule-specific cysteine-rich (NCR) small peptides that are expressed in the symbiotic organ, the root nodule, where they control terminal differentiation of the endosymbiotic rhizobium bacteria to nitrogen-fixing bacteroids. Cationic NCR peptides were predicted to have antimicrobial activities. Here antibacterial activities of NCR247, NCR335, polymyxin B (PMB), and streptomycin were investigated and compared on two foodborne pathogens Salmonella enterica and Listeria monocytogenes as representatives of Gram-negative and Gram-positive bacteria. The integrity of the bacterial membrane was seriously compromised by these NCR peptides. Different localization was observed for NCR247 and NCR335 in the treated bacteria, the peptides mostly accumulated in the cytosol in S. enterica while they remained in the bacterial membrane in L. monocytogenes. Scanning electron microscopy revealed distinct membrane morphology of the peptide-treated bacteria. Complete cell disruption was induced by PMB and NCR335 in S. enterica while NCR247 treatment resulted in extensive budding observed on the cell surface of Salmonella. PMB had no effect on L. monocytogenes while NCR335 and NCR247 provoked morphological changes on this bacterium, the whole Listeria cell content was released in response to NCR335 treatment.
Highlights
Antimicrobial peptides (AMPs) are considered as natural antibiotics produced by all kinds of living organisms including bacteria (Joerger, 2003; Hassan et al, 2012), plants (Benko-Iseppon et al, 2010), and animals (Hancock and Scott, 2000)
The results indicated that the bactericidal effect of nodule-specific cysteinerich (NCR) peptides on S. enterica and L. monocytogenes is directly realized through membrane permeabilization and damage
NCR247 and NCR335 peptides are members of the NCR peptide family discovered in M. truncatula (Mergaert et al, 2003; Nallu et al, 2014)
Summary
Antimicrobial peptides (AMPs) are considered as natural antibiotics produced by all kinds of living organisms including bacteria (Joerger, 2003; Hassan et al, 2012), plants (Benko-Iseppon et al, 2010), and animals (Hancock and Scott, 2000). Hundreds of AMP molecules have been isolated from prokaryotes to humans and plants (Maróti et al, 2011). They represent a cornerstone of the innate immune system in higher eukaryotes. Different AMPs show variations in their antimicrobial activity spectrum which ranges from Gram-positive and Gram-negative bacteria (including multidrug resistant pathogens) to viruses and fungi. Insights into AMPs natural environment and their possible natural roles have shown
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