Bactericidal Compounds Controlling Growth of the Plant Pathogen Pseudomonas syringae pv. actinidiae, Which Forms Biofilms Composed of a Novel Exopolysaccharide

Abstract

c Pseudomonas syringae pv. actinidiae is the major cause of bacterial canker and is a severe threat to kiwifruit production worldwide. Many aspects of the disease caused by P. syringae pv. actinidiae, such as the pathogenicity-relevant formation of a biofilm composed of extracellular polymeric substances (EPSs), are still unknown. Here, a highly virulent strain of P. syringae pv. actinidiae, NZ V-13, was studied with respect to biofilm formation and architecture using a flow cell system combined with confocal laser scanning microscopy. The biofilm formed by P. syringae pv. actinidiae NZ V-13 was heterogeneous, consisting of a thin cellular base layer 5 m thick and microcolonies with irregular structures. The major component of the EPSs produced by P. syringae pv. actinidiae NZ V-13 bacteria was isolated and identified to be an exopolysaccharide. Extensive compositional and structural analysis showed that rhamnose, fucose, and glucose were the major constituents, present at a ratio of 5:1.5:2. Experimental evidence that P. syringae pv. actinidiae NZ V-13 produces two polysaccharides, a branched ␣-D-rhamnan with side chains of terminal ␣-D-Fucf and an ␣-D-1,4-linked glucan, was obtained. The susceptibility of the cells in biofilms to kasugamycin and chlorine dioxide was assessed. About 64 and 73% of P. syringae pv. actinidiae NZ V-13 cells in biofilms were killed when kasugamycin and chlorine dioxide were used at 5 and 10 ppm, respectively. Kasugamycin inhibited the attachment of P. syringae pv. actinidiae NZ V-13 to solid surfaces at concentrations of 80 and 100 ppm. Kasugamycin was bacteriostatic against P. syringae pv. actinidiae NZ V-13 growth in the planktonic mode, with the MIC being 40 to 60 ppm and a bactericidal effect being found at 100 ppm. Here we studied the formation, architecture, and composition of P. syringae pv. actinidiae biofilms as well as used the biofilm as a model to assess the efficacies of bactericidal compounds. P seudomonas syringae pv. actinidiae is the main cause of kiwifruit canker, which is epidemic worldwide (1-3). The P. syringae pv. actinidiae epidemic in New Zealand is threatening the kiwifruit industry, which is the second most important horticultural export crop by monetary value in New Zealand. In New Zealand, the highly virulent strain P. syringae pv. actinidiae V was reported in 2010 in the Bay of Plenty region and caused an estimated 50% loss of vines of the Hort16A kiwifruit variety known as Zespri Gold (4-6). This bacterial disease can affect all commercial species of kiwifruit (3,7,8). The main distinctive symptoms of disease are cankers on the vines and trunks, gummosis, dieback of the canes, wilting, and sometimes death of the vines (5).Similar to other pseudomonads, P. syringae pv. actinidiae can form cell communities known as biofilms. The formation of biofilms is a physiological response to environmental stresses mediated by the regulation of specific sets of genes, including genes encoding virulence factors. Biofilm formation protects cells against host defense me...

Redox properties of extracellular polymeric substances (EPS) from electroactive bacteria

“…Polysaccharides were determined using the anthrone method33 with glucose as the standard. Uronic acids were measured using the m -hydroxydiphenyl sulfuric acid method34 with glucuronic acid as the standard. Heme was quantified in a fluorescence assay35 with bovine heart cytochrome c (95%, Aladdin Co., USA) as the standard.…”

Bacterial pathogenesis of plants: future challenges from a microbial perspective

“…The aggressive kiwi pathogen P. syringae pv. actinidiae (Psa) NZ V-13 produces two novel, previously uncharacterized, polysaccharides: a branched a-D-rhamnan and an a-D-1,4-linked glucan polymer (Ghods et al, 2015). The genomes of P. syringae pathovars also encode a number of EPS loci that have been characterized in other Pseudomonas species, but whose contribution to plant infection is undefined.…”

Unraveling the photoactive annihilation mechanism of nanostructures as effective green tools for inhibiting the proliferation of the phytopathogenic bacteriumPseudomonas syringae

“…Other methods to control infections are the use of oxidizing disinfectants such as ozone and chlorine dioxide, UV light treatment, chlorination and peroxide oxidation. 2,[12][13][14][15] Most chemicals, bactericides and fungicides react with organic matter and other precursors to form regulated and emerging disinfection by-products, which can be associated with cancer or other human pathologies. 14,15 The most recent method to control phytopathogenic bacteria is the use of transgenic products like cotton, tomato, soybean, potato, etc.…”