Bacteria from the citrus phylloplane can disrupt cell–cell signalling in Xanthomonas citri and reduce citrus canker disease severity

Abstract

Xanthomonas citri subsp. citri (Xcc) is the causal agent of citrus canker, a disease that affects almost all types of citrus crops. Production of particular Xcc pathogenicity factors is controlled by a gene cluster rpf, which encodes elements of a cell-cell communication system called quorum sensing (QS), mediated by molecules of the diffusible signal factor (DSF) family. Interference with cell-cell signalling, also termed quorum quenching, either by signal degradation or over-production, has been suggested as a strategy to control bacterial disease. In this study, three bacterial strains were isolated from citrus leaves that displayed the ability to disrupt QS signalling in Xcc. Pathogenicity assays in sweet orange (Citrus sinensis) showed that bacteria of the genera Pseudomonas and Bacillus also have a strong ability to reduce the severity of citrus canker disease. These effects were associated with alteration in bacterial attachment and biofilm formation, factors that are known to contribute to Xcc virulence. These quorum-quenching bacteria may represent a highly valuable tool in the process of biological control and offer an alternative to the traditional copper treatment currently used to treat citrus canker disease.

Diffusible signal factor-dependent quorum sensing in pathogenic bacteria and its exploitation for disease control

“…Inoculation of bacteria able to degrade DSF can reduce virulence and symptom production by Xy. fastidiosa in grape, Xcc in brassica and Xanthomonas citri in citrus Caicedo et al 2016). Taken together, these findings suggest that it should be possible to select further strains for improved biocontrol of plant diseases, particularly those caused by xanthomonads.…”

“…; Caicedo et al . ). A mutational analysis in Pseudomonas species strain G indicated a role for carAB in rapid DSF inactivation/degradation (Newman et al .…”

“…; Caicedo et al . ). Taken together, these findings suggest that it should be possible to select further strains for improved biocontrol of plant diseases, particularly those caused by xanthomonads.…”

“…A functional screen showed that many bacteria have the ability to degrade DSF, with some strains belonging to genera Bacillus, Paenibacillus, Microbacterium, Staphylococcus and Pseudomonas capable of particularly rapid degradation Caicedo et al 2016). A mutational analysis in Pseudomonas species strain G indicated a role for carAB in rapid DSF inactivation/degradation .…”

Biological Control of Citrus Canker: New Approach for Disease Control

“…From a total of 114 isolates recovered, 7 bacteria able to disrupt DSF quorum sensing pathway in Xac (quorum quencher bacteria) were identified. These bacteria were identified by API kits (bioMérieux's API®) and sequencing of PCR-mediated amplification products of the 16S rRNA genes as Bacillus amyloliquefaciens, Bacillus vallismortis, Pseudomonas oryzihabitans, Pseudomonas aeruginosa, Raoultella planticola, Kosakonia cowanii, and Citrobacter freundii [33].…”