Exposure to Umbelliferone Reduces Ralstonia solanacearum Biofilm Formation, Transcription of Type III Secretion System Regulators and Effectors and Virulence on Tobacco

Abstract

Ralstonia solanacearum is one of the most devastating phytopathogens and causes bacterial wilt, which leads to severe economic loss due to its worldwide distribution and broad host range. Certain plant-derived compounds (PDCs) can impair bacterial virulence by suppressing pathogenic factors of R. solanacearum. However, the inhibitory mechanisms of PDCs in bacterial virulence remain largely unknown. In this study, we screened a library of coumarins and derivatives, natural PDCs with fused benzene and α-pyrone rings, for their effects on expression of the type III secretion system (T3SS) of R. solanacearum. Here, we show that umbelliferone (UM), a 7-hydroxycoumarin, suppressed T3SS regulator gene expression through HrpG–HrpB and PrhG–HrpB pathways. UM decreased gene expression of six type III effectors (RipX, RipD, RipP1, RipR, RipTAL, and RipW) of 10 representative effector genes but did not alter T2SS expression. In addition, biofilm formation of R. solanacearum was significantly reduced by UM, though swimming activity was not affected. We then observed that UM suppressed the wilting disease process by reducing colonization and proliferation in tobacco roots and stems. In summary, the findings reveal that UM may serve as a plant-derived inhibitor to manipulate R. solanacearum T3SS and biofilm formation, providing proof of concept that these key virulence factors are potential targets for the integrated control of bacterial wilt.

A putative LysR‐type transcriptional regulator PrhO positively regulates the type III secretion system and contributes to the virulence of Ralstonia solanacearum

“…prhO deletion did not alter the expression of prhJ , phcA and prhN , which are known to be important for the expression of hrpG and prhG (Hikichi et al ., ; Zhang et al ., ), indicating that the regulation of PrhO on the expression of hrpG and prhG is independent of these known regulating pathways. Recently, we have identified a plant‐derived compound, umbelliferone, which impairs T3SS expression via HrpG and PrhG, but independent of these known regulators (Yang et al ., ), supporting our speculation that certain novel pathways should be integrated for the expression of hrpG and prhG in R. solanacearum . It should be noted that HrpB is not expressed until contact with hrp ‐inducing medium or with host plants, whereas HrpG is best expressed in rich medium.…”

Coumarin: a novel player in microbial quorum sensing and biofilm formation inhibition

“…It is worth noting that the best antimicrobial activities were also displayed by these same coumarins, raising the possibility that the biofilm suppression may simply reflect the limitation of growth under these conditions. The authors subsequently followed up this study with analysis of umbelliferone and its antivirulence activity against R. solanacearum (Yang et al 2017 ). The type three secretion system (T3SS) and biofilm formation were both suppressed.…”

“…Coumarins are a large family of naturally derived fused benzene and a-pyrone rings found primarily in a wide range of plant sources. Some coumarins are regarded as phytoalexins which are plant resistance compounds that are biosynthesised by plant tissues in response to pathogenic infection (Yang et al 2017 ). Members of the coumarin class of compound have also been identified in bacteria and fungi, such as novobiocin and coumermycin isolated from Streptomyces (Eustaquio et al 2003 ), and aflatoxins isolated from different Aspergillus species (Kumar et al 2016 ).…”

Nutrient Removal and Uptake by Native Planktonic and Biofilm Bacterial Communities in an Anaerobic Aquifer

“…These greater rates of nutrient removal by the biofilm communities is assumed to be the result of the greater microbial biomass associated with this niche, relative to the planktonic communities. Though not determined during this study, biofilms have also been shown to support microbial groups with physiological capabilities for the metabolism of nutrients that are not associated with the planktonic communities ( Nadell et al, 2016 ; Stubbendieck et al, 2016 ; Jones and Bennett, 2017 ).…”