Disruption ofcomAhomolog inRalstonia solanacearumdoes not impair its twitching motility

Novel mandelic acid derivatives suppress virulence of Ralstonia solanacearum via type III secretion system

BACKGROUND

Bacterial wilt induced by Ralstonia solanacearum is regarded as one of the most devastating diseases. However, excessive and repeated use of the same bactericides has resulted in development of bacterial resistance. Targeting bacterial virulence factors, such as type III secretion system (T3SS), without inhibiting bacterial growth is a possible assay to discover new antimicrobial agents.

RESULTS

In this work, identifying new T3SS inhibitors, a series of mandelic acid derivatives with 2-mercapto-1,3,4-thiazole moiety was synthesized. One of them, F-24, inhibited the transcription of hrpY gene significantly. The presence of this compound obviously attenuated hypersensitive response (HR) without inhibiting bacterial growth of R. solanacearum. The transcription levels of those typical T3SS genes were reduced to various degrees. The test of the ability of F-24 in protecting plants demonstrated that F-24 protected tomato plants against bacterial wilt without restricting the multiplication of R. solanacearum. The mechanism of this T3SS inhibition is through the PhcR-PhcA-PrhG-HrpB pathway.

CONCULSION

The screened F-24 could inhibit R. solanacearum T3SS and showed better inhibitory activity than previously reported inhibitors without affecting the growth of the strain, and F-24 is a compound with good potential in the control of R. solanacearum. © 2023 Society of Chemical Industry.

Gallic Acid an Agricultural Byproduct Modulates the Biofilm Matrix Exopolysaccharides of the Phytopathogen Ralstonia solanacearum

Ralstonia solanacearum is a soil-borne plant pathogen which causes wilt disease in economically important crops of the Solanaceae family in tropical and temperate regions. As biofilm formation is the major virulence factor in R. solanacearum, research inputs are necessary to identify natural biofilm inhibitors to mitigate virulence of this bacterium. Hence in the present work, the anti-biofilm potential of phytochemical compound gallic acid (GA) isolated from an agricultural byproduct (cashewnut shell) was investigated. Initially the Minimum inhibitory concentration (MIC) of crude extracts of cashewnut shell and coconut shell against R. solanacearum were investigated. The MIC of both the extracts were 400 µg/ml and their sub-MIC (200 µg/ml) inhibited biofilms in the range of 62-70% and 49-57%, respectively. As the cashewnut shell extract have higher biofilm inhibitory effect compared to coconut shell extract, we proceeded our further study by isolating the major compound GA from cashewnut shell by acid hydrolysate method. The sub-MIC of crude cashewnut shell extract inhibited 85% of young biofilms. The MIC of GA were observed at 3 mg/ml and sub-MIC (1.5 mg/ml) was found to eradicate 85% of mature biofilms which was confirmed by standard crystal violet assay and the biofilm reduction was further visualized under light microscopy and scanning electron microscopic images. Toxicity of GA was evaluated against R. solanacearum through XTT cell viability assay and found no antibacterial effect at sub-MIC. Additionally, it is confirmed with growth curve and time kill assays. Swimming and twitching motility were considered as an important virulence factors to invade plants and to block the xylem vessels. Therefore, sub-MIC of GA was found to inhibit both swimming and twitching motility of about 93% and 63% respectively. Anti-biofilm efficacy of GA was also worked well with tomato plant model where remarkable biofilm inhibition was found on treatment with GA before and after 24 h of infection with R. solanacearum. Hence GA will be an alternative, cheap source which is eco-friendly as well as novel source for the treatment of R. solanacearum biofilms and to prevent wilt disease in important crops.

Introduction of Genetic Material in Ralstonia solanacearum Through Natural Transformation and Conjugation

Ralstonia solanacearum is a soil-borne plant pathogen, responsible of the bacterial wilt disease. Its unusual wide host range (more than 250 plant species), aggressiveness, and broad geographic distribution have made of this bacterium the main plant pathogenic model in the beta-Proteobacteria class. Many R. solanacearum strains have the ability to internalize exogenous DNA through natural transformation. This property is widely used in reverse genetics studies to create mutants or reporter gene constructs, in the aim to study the molecular bases of pathogenesis of this bacterium. In this chapter, we describe three in vitro methods (natural transformation, electrotransformation, and conjugation) commonly used to produce recombinant R. solanacearum cells after introduction of exogenous DNA.