Pseudomonas fluorescens MFE01 delivers a putative type VI secretion amidase that confers biocontrol against the soft‐rot pathogen Pectobacterium atrosepticum

• Published in: Environmental microbiology 2023-11, Vol.25 (11), p.2564-2579
• Main Authors: Bourigault, Yvann, Dupont, Charly A., Desjardins, Jonas B., Doan, Thierry, Bouteiller, Mathilde, Le Guenno, Hugo, Chevalier, Sylvie, Barbey, Corinne, Latour, Xavier, Cascales, Eric, Merieau, Annabelle
• Format: Article
• Language: English
• Subjects: Aggressive behavior; Aggressive behaviour; Amidase; Biological control; Cell walls; Contractility; Coupled walls; Environmental Sciences; Firing pattern; Fluorescence; Fluorescence microscopy; Gram-negative bacteria; Immunity; Life Sciences; Membrane proteins; Microorganisms; Mutagenesis; Pathogenesis; Pectobacterium atrosepticum; Periplasm; Potatoes; Pseudomonas fluorescens; Secretion; Target cells; Toxicity
• ISSN: 1462-2912; 1462-2920
• DOI: 10.1111/1462-2920.16492

The type VI secretion system (T6SS) is a contractile nanomachine widespread in Gram‐negative bacteria. The T6SS injects effectors into target cells including eukaryotic hosts and competitor microbial cells and thus participates in pathogenesis and intermicrobial competition. Pseudomonas fluorescens MFE01 possesses a single T6SS gene cluster that confers biocontrol properties by protecting potato tubers against the phytopathogen Pectobacterium atrosepticum (Pca). Here, we demonstrate that a functional T6SS is essential to protect potato tuber by reducing the pectobacteria population. Fluorescence microscopy experiments showed that MFE01 displays an aggressive behaviour with an offensive T6SS characterized by continuous and intense T6SS firing activity. Interestingly, we observed that T6SS firing is correlated with rounding of Pectobacterium cells, suggesting delivery of a potent cell wall targeting effector. Mutagenesis coupled with functional assays then revealed that a putative T6SS secreted amidase, Tae3Pf, is mainly responsible for MFE01 toxicity towards Pca. Further studies finally demonstrated that Tae3Pf is toxic when produced in the periplasm, and that its toxicity is counteracted by the Tai3Pf inner membrane immunity protein. Pseudomonas fluorescens MFE01 uses a type VI secretion system (T6SS) to confer potato protection against the phytopathogen Pectobacterium atrosepticum. P. fluorescens MFE01 type VI secretion causes Pca cell rounding. The P. fluorescens T6SS delivers a putative periplasmic‐acting amidase.