Phage‐selected lipopolysaccharide mutants of Pectobacterium atrosepticum exhibit different impacts on virulence

Abstract

Aims: To positively select Pectobacterium atrosepticum (Pa) mutants with cell surface defects and to assess the impact of these mutations on phytopathogenesis. Methods and Results: Several phages were isolated from treated sewage effluent and were found to require bacterial lipopolysaccharide (LPS) for infection. Two strains with distinct mutations in LPS were obtained by transposon mutagenesis. Along with a third LPS mutant, these strains were characterized with respect to various virulence‐associated phenotypes, including growth rate, motility and exoenzyme production, demonstrating that LPS mutations are pleiotropic. Two of the strains were deficient in the synthesis of the O‐antigen portion of LPS, and both were less virulent than the wild type. A waaJ mutant, which has severe defects in LPS biosynthesis, was dramatically impaired in potato tuber rot assays. The infectivity of these novel phages on 32 additional strains of Pa was tested, showing that most Pa isolates were sensitive to the LPS‐dependent phages. Conclusions: Native LPS is crucial for optimal growth, survival and virulence of Pa in vivo, but simultaneously renders such strains susceptible to phage infection. Significance and Impact of the Study: This work demonstrates the power of phages to select and identify the virulence determinants on the bacterial surface, and as potential biocontrol agents for Pa infections.

Surface swarming motility by Pectobacterium atrosepticum is a latent phenotype that requires O antigen and is regulated by quorum sensing

“…None of the genes encoding the enterobacterial common antigen [encoded by wecAAwecG (ECA4210-ECA4200)] were hit in our screen, indicating that O antigen biosynthesis is likely to be the major contributor towards the observed swarming phenotype. In a previous study, Evans et al (2010) showed that a mutant in the rfbI gene (encoding CDP-6-deoxydelta-3,4-glucoseen reductase) of HAI5 was less susceptible to infection by an LPS-dependent bacteriophage and also lacked O antigen (although it retained the enterobacterial common antigen). It therefore appears that HAI5 encodes the main O antigen biosynthetic cluster in Pca.…”

Deciphering the dual effect of lipopolysaccharides from plant pathogenicPectobacterium

“…It plays a major role for bacterial growth and survival. 8,9 Structurally, LPS is a glycoconjugate, tripartite molecule, consisting of a hydrophobic lipid part (lipid A), a core oligosaccharide and an O-polysaccharide part (OPS). 10,11 Although, recognition of some MAMPs seemed to occur through pattern recognition receptors, 12,13 LPS recognitions in plants remains little-known.…”

“…22 The LPS from the plant pathogen Pectobacterium atrosepticum (Pa) seems to be crucial not only for optimal growth and survival of the bacteria but for its virulence as well. 9,[23][24][25] It was shown to induce different early responses such as acidification of the medium. 26 The fact that LPS induced variable cellular responses can be attributed to LPS preparations, plants and cell types used and reflect the ability of particular plants to recognize structural features within LPS that are not widely conserved.…”

“…34,36 Although in previous studies on animal cells, the main biological activities was described to be exerted by lipid A, 34,73 the lipid A of P. carotovorum and E. coli LPS exhibit the same biological activity. 34 However other studies point out that in plant the 3 parts of the LPS, the lipid A, the core oligosaccharide and the OPS could be active in virulence, 9,74 in defense-related gene induction 16,18 , 75,76 and HR suppression. [75][76][77] In A. thaliana leaves, the defense responses occurred in 2 phases, the core oligosaccharide inducing an early phase and the lipid A moiety only a later phase 75 suggesting a differential recognition of these molecular motifs.…”

“…Although part of the responses to both types of LPS could overlap, different signaling pathways could be activated, and among the LPS-induced responses the differential kinetics and amplitude in ROS generation seems to be determinants to induce PCD in A. thaliana cells, allowing putative role of LPS from Pectobaterium in virulence, as previously reported for LPS Pa . 9,23 Further studies will be needed to determine the roles of the different parts of the LPS molecules in inducing the different signaling pathways activated in plant cells.…”