Proteomic comparison of Ralstonia solanacearum strains reveals temperature dependent virulence factors

Abstract

BackgroundRalstonia solanacearum, the causal agent of bacterial wilt, is a genetically diverse bacterial plant pathogen present in tropical and subtropical regions of the world that infects more than 200 plant species, including economically important solanaceous crops. Most strains of R. solanacearum are only pathogenic at temperatures between 25 to 30°C with strains that can cause disease below 20°C considered a threat to agriculture in temperate areas. Identifying key molecular factors that distinguish strains virulent at cold temperatures from ones that are not is needed to develop effective management tools for this pathogen. We compared protein profiles of two strains virulent at low temperature and two strains not virulent at low temperature when incubated in the rhizosphere of tomato seedlings at 30 and 18°C using quantitative 2D DIGE gel methods. Spot intensities were quantified and compared, and differentially expressed proteins were sequenced and identified by mass spectrometry (MS/MS).ResultsFour hundred and eighteen (418) differentially expressed protein spots sequenced produced 101 unique proteins. The identified proteins were classified in the Gene Ontology biological processes categories of metabolism, cell processes, stress response, transport, secretion, motility, and virulence. Identified virulence factors included catalase (KatE), exoglucanase A (ChbA), drug efflux pump, and twitching motility porin (PilQ). Other proteins identified included two components of a putative type VI secretion system. We confirmed differential expression of 13 candidate genes using real time PCR techniques. Global regulators HrpB and HrpG also had temperature dependent expression when quantified by real time PCR.ConclusionsThe putative involvement of the identified proteins in virulence at low temperature is discussed. The discovery of a functional type VI secretion system provides a new potential virulence mechanism to explore. The global regulators HrpG and HrpB, and the protein expression profiles identified suggest that virulence at low temperatures can be partially explained by differences in regulation of virulence factors present in all the strains.

Seasonal variation in the biocontrol efficiency of bacterial wilt is driven by temperature‐mediated changes in bacterial competitive interactions

“…; Bocsanczy et al . ). While these hypotheses remain to be tested in future experiments, our preliminary data suggest that only very cold temperatures (around 4 °C) and very hot temperatures (around 37 °C) lead to the emergence of small R. solanacearum colony variants indicative of lowered pathogen virulence (see Fig.…”

“…High temperature (32°C) has also been found to directly increase the severity of bacterial wilt in two tomato lines (Philippine 1169 and Hawaii 7580) (Krausz & Thurston 1975). In contrast, low soil temperatures could reduce disease development by directly inducing tomato resistance (Mew & Ho 1977) or by attenuating R. solanacearum virulence via lowered or lost twitching motilitya trait important for plant root colonization and invasion (Kang et al 2002;Bocsanczy et al 2014). While these hypotheses remain to be tested in future experiments, our preliminary data suggest that only very cold temperatures (around 4°C) and very hot temperatures (around 37°C) lead to the emergence of small R. solanacearum colony variants indicative of lowered pathogen virulence (see Fig.…”

“…Second, high temperature could affect the virulence expression of the pathogen: most strains of R. solanacearum are only pathogenic at temperatures between 25 and 35 °C, with the exception of Race 3 strains that are able to cause disease below 20 °C (Bocsanczy et al . ). Third, changes in temperature could affect the pathogen suppression by having effects on plant immune responses (Cheng Cheng et al .…”

“…For example, the pathogen and biocontrol strains might have different growth optima, and thus, temperature changes could affect the strength of resource or interference competition between the strains. Second, high temperature could affect the virulence expression of the pathogen: most strains of R. solanacearum are only pathogenic at temperatures between 25 and 35°C, with the exception of Race 3 strains that are able to cause disease below 20°C (Bocsanczy et al 2014). Third, changes in temperature could affect the pathogen suppression by having effects on plant immune responses (Cheng Cheng et al 2013) or non-bacterial micro-organisms present in the microbiome (Waldrop & Firestone 2006).…”

Global Gene Expression Analysis of Cross-Protected Phenotype of Pectobacterium atrosepticum

“…Persistence under unfavorable conditions is common for many plant pathogenic bacteria since the life cycle of their host plants usually depends on seasonal changes [18]. Therefore, phytopathogens have adapted to survival in various ecological niches, including water, soil, insects, etc [19–21].…”