A Single Promoter Inversion Switches Photorhabdus Between Pathogenic and Mutualistic States

• Published in: Science (American Association for the Advancement of Science) Vol. 337; no. 6090; pp. 88 - 93
• Main Authors: Somvanshi, Vishal S., Sloup, Rudolph E., Crawford, Jason M., Martin, Alexander R., Heidt, Anthony J., Kim, Kwi-suk, Clardy, Jon, Ciche, Todd A.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 06.07.2012; The American Association for the Advancement of Science
• Subjects: Animals; Antibiotics; Bacteria; Bacteriology; Biological and medical sciences; Delta cells; Drug resistance; Fimbriae Proteins - genetics; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial; Genes; Genetics; Genome, Bacterial; Infections; Insect colonies; Insects; Intestines; Intestines - microbiology; Microbiology; Moths - microbiology; Mutation; Mutualism; Nematodes; Nutrients; Pathogenesis; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Pathogens; Phenotype; Phenotypes; Photorhabdus; Photorhabdus - cytology; Photorhabdus - genetics; Photorhabdus - growth & development; Photorhabdus - pathogenicity; Promoter Regions, Genetic; Rhabditoidea - microbiology; Sequence Inversion; Switches; Symbiosis; Toxins; Virulence; Virulence - genetics; Animal microorganism relation; Transcription promoter; Insecta; Inversion; Mutualism; Pathogenicity; Arthropoda; Helmintha; Bacteria; Nemathelminthia; Invertebrata; Nematoda; Enterobacteriaceae
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1216641

Microbial populations stochastically generate variants with strikingly different properties, such as virulence or avirulence and antibiotic tolerance or sensitivity. Photorhabdus luminescens bacteria have a variable life history in which they alternate between pathogens to a wide variety of insects and mutualists to their specific host nematodes. Here, we show that the P. luminescens pathogenic variant (P form) switches to a smaller-cell variant (M form) to initiate mutualism in host nematode intestines. A stochastic promoter inversion causes the switch between the two distinct forms. M-form cells are much smaller (one-seventh the volume), slower growing, and less bioluminescent than P-form cells; they are also avirulent and produce fewer secondary metabolites. Observations of form switching by individual cells in nematodes revealed that the M form persisted in maternal nematode intestines, were the first cells to colonize infective juvenile (l]) offspring, and then switched to P form in the IJ intestine, which armed these nematodes for the next cycle of insect infection.