autophagic machinery ensures nonlytic transmission of mycobacteria

• Published in: Proceedings of the National Academy of Sciences - PNAS 2015-02, Vol.112 (7), p.E687-E692
• Main Authors: Gerstenmaier, Lilli, Pilla, Rachel, Herrmann, Lydia, Herrmann, Hendrik, Prado, Monica, Villafano, Geno J., Kolonko, Margot, Reimer, Rudolph, Soldati, Thierry, King, Jason S., Hagedorn, Monica
• Format: Article
• Language: English
• Subjects: Autophagy; Bacteria; Biological Sciences; Cells; Dictyostelium - microbiology; Fluorescent Antibody Technique; Membranes; Microscopy, Electron, Transmission; Mycobacterium - physiology; Mycobacterium - ultrastructure; PNAS Plus
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1423318112

Significance Pathogenic mycobacteria can be transmitted by direct ejection from one host cell to another. However, the mechanism of ejection, and how lysing the host cell is prevented are unknown. This study explains how the host cell remains intact and alive while Mycobacterium marinum breaks through its plasma membrane during ejection. We show that a membraneous cup is specifically recruited to the distal pole of ejecting M. marinum . We demonstrate that these membranes are formed by the canonical autophagic pathway, though they do not mature to autophagolysosomes. Disruption of autophagy causes the host cells to become leaky and die during ejection. This dramatically reduces cell-to-cell transmission of the infection, demonstrating an important and unexpected role for autophagy in maintaining plasma membrane integrity during mycobacterial infection. In contrast to mechanisms mediating uptake of intracellular bacterial pathogens, bacterial egress and cell-to-cell transmission are poorly understood. Previously, we showed that the transmission of pathogenic mycobacteria between phagocytic cells also depends on nonlytic ejection through an F-actin based structure, called the ejectosome. How the host cell maintains integrity of its plasma membrane during the ejection process was unknown. Here, we reveal an unexpected function for the autophagic machinery in nonlytic spreading of bacteria. We show that ejecting mycobacteria are escorted by a distinct polar autophagocytic vacuole. If autophagy is impaired, cell-to-cell transmission is inhibited, the host plasma membrane becomes compromised and the host cells die. These findings highlight a previously unidentified, highly ordered interaction between bacteria and the autophagic pathway and might represent the ancient way to ensure nonlytic egress of bacteria.