A Single Promoter Inversion Switches Photorhabdus Between Pathogenic and Mutualistic States

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Science  06 Jul 2012:
Vol. 337, Issue 6090, pp. 88-93
DOI: 10.1126/science.1216641

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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 (IJ) offspring, and then switched to P form in the IJ intestine, which armed these nematodes for the next cycle of insect infection.

  • * Present address: Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.

  • Present address: Department of Chemistry and Chemical Biology Institute, Yale University, New Haven, CT 06520, USA.

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