A membrane localized RTX-like protein mediates physiochemical properties of the Pantoea stewartii cell envelope that impact surface adhesion, cell surface hydrophobicity and plant colonization

Authors: VIRAVATHANA, POLRIT - University Of California, Riverside; Burbank, Lindsey; JABLONSKA, BARBARA - University Of California, Riverside; SUN, QIANG - University Of Wisconsin; ROPER, CAROLINE - University Of California, Riverside

Submitted to: BMC Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Pantoea stewartii subsp. stewartii is a bacterial pathogen that causes Stewart’s wilt disease of sweet corn. Disease symptoms include seedling wilt and water-soaking of leaf tissue. Understanding how this pathogen damages plant tissue is important for disease mitigation. This study describes how a protein (RTX2) on the outside of bacterial cells is necessary for the bacteria to attach to plant cells as well as for plant cell damage associated with disease. These findings are important for developing new disease management strategies targeting Pantoea stewartii in corn, and may also be applicable to other bacterial diseases in agriculture.

Technical Abstract: Pantoea stewartii subsp. stewartii, is the bacterial causal agent of Stewart’s wilt of sweet corn. Disease symptoms include systemic wilting and foliar, water-soaked lesions. A Repeat-in-toxin (RTX)-like protein, RTX2, causes cell leakage and collapse in the leaf apoplast of susceptible corn varieties and is a primary mediator of water-soaked lesion formation in the P. stewartii/sweet corn pathosystem. RTX toxins comprise a large family of proteins, which are widely distributed among Gram-negative bacteria. These proteins are generally categorized as cellulolysins, but the Biofilm-Associated Proteins (BAP) subfamily of RTX toxins are implicated in surface adhesion and other biofilm behaviors. RTX2 is most phylogenetically related to other BAP proteins suggesting that P. stewartii RTX2 plays a dual role in adhesion to host surfaces in addition to mediating the host cell lysis that leads to water-soaked lesion formation. This study demonstrated that RTX2 localizes to the bacterial cell envelope and influences physiochemical properties of the bacterial cell envelope that influence bacterial cell length, cell envelope integrity and overall cellular hydrophobicity. Interestingly, the role of RTX2 as an adhesin was only evident in absence of exopolysaccharide (EPS) production suggesting that RTX2 plays a nuanced role as an adhesin early in the biofilm development before EPS production is induced. However, deletion of rtx2 severely impacted colonization of the xylem suggesting that dual role of RTX2 as a cytolysin and adhesin that links the apoplastic water-soaked lesion phase of infection to the wilting phase of the infection in the xylem.