Active invasion of bacteria into living fungal cells

• DOI: 10.7554/elife.03007
• Publication Date: 2014-09-01T11:32:34Z
• Authors: Nadine Moebius; Zerrin Üzüm; Jan Dijksterhuis; Gerald Lackner; Christian Hertweck
• Keywords: Proteomics; 0301 basic medicine; Proteome; QH301-705.5; Burkholderia; Science; Hyphae; Type 2 secretion system; 03 medical and health sciences; Electrophoresis, Gel, Two-Dimensional; Biology (General); Symbiosis; Plant Diseases; Microbiology and Infectious Disease; Microscopy, Confocal; Q; Chitinases; Cryoelectron Microscopy; Chitinase; R; Oryza; symbiosis; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Host-Pathogen Interactions; Mutation; Microscopy, Electron, Scanning; Medicine; Macrolides; Rhizopus

The rice seedling blight fungus Rhizopus microsporus and its endosymbiont Burkholderia rhizoxinica form an unusual, highly specific alliance to produce the highly potent antimitotic phytotoxin rhizoxin. Yet, it has remained a riddle how bacteria invade the fungal cells. Genome mining for potential symbiosis factors and functional analyses revealed that a type 2 secretion system (T2SS) of the bacterial endosymbiont is required for the formation of the endosymbiosis. Comparative proteome analyses show that the T2SS releases chitinolytic enzymes (chitinase, chitosanase) and chitin-binding proteins. The genes responsible for chitinolytic proteins and T2SS components are highly expressed during infection. Through targeted gene knock-outs, sporulation assays and microscopic investigations we found that chitinase is essential for bacteria to enter hyphae. Unprecedented snapshots of the traceless bacterial intrusion were obtained using cryo-electron microscopy. Beyond unveiling the pivotal role of chitinolytic enzymes in the active invasion of a fungus by bacteria, these findings grant unprecedented insight into the fungal cell wall penetration and symbiosis formation.