BF V3 275

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Sunday, 14 October 2018 20:36

elegans Endures Edifying Enterococcus - BacterioFiles 358

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Published in Bacteriofiles

This episode: Roundworms and not-too-irritating bacteria quickly evolve a beneficial relationship when under threat from other bacterial pathogens!

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(7.5 MB, 8.1 minutes)

Show notes: 

bf297elegansMicrobe of the episode: Siegesbeckia yellow vein betasatellite

News item

Journal Paper:
Rafaluk‐Mohr C, Ashby B, Dahan DA, King KC. 2018. Mutual fitness benefits arise during coevolution in a nematode-defensive microbe model. Evol Lett 2:246–256.

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Episode outline:

  • Background: Microbes everywhere in and around bodies
    • Despite tiny size, lots of them
    • Can have major effects on hosts, good or bad
  • Many beneficial microbes form long-term relationships with hosts
    • Evolve together, dependent on each other
    • But how do these relationships start?
  • What’s new: Now, scientists publishing in Evolution Letters have discovered that a bacterium in roundworms is mildly harmful by itself but helpful in protecting the worms from worse pathogens!
  • Worms are Caenorhabditis elegans, common model lab organism
    • Every cell in body is well understood
  • Enterococcus faecalis prevents worms from thriving as much when alone
    • But not as virulent/harmful as bacterium Staphylococcus aureus
  • Methods: Let worms and bacteria evolve together over generations
    • Either alone or under threat from Staphylococcus
  • Relationship of protection developed strongly under threat, 5% more host survival
    • Took 14 generations for relationship to develop
    • Worms evolved along with Enterococcus bacteria did better than ancestral worm strain
    • Similar with worms evolved with bacteria in absence of Staphylococcus threat
  • Made mathematical model of system to make predictions
    • Prediction: mutualism most likely to evolve when helpful bacteria are moderately helpful
    • If not very helpful, only costly, host shuts them out
    • If too helpful, pathogen is not a threat and goes away, so then helpful are only harmful
    • But if helpful is just helpful enough, host keeps them around for continuing protection
  • Summary: Worms and microbes that evolved together benefit each other more than worms not evolved to work with the microbes or microbes not evolved to work with the worms
  • Applications and implications: Relevant to health – our microbe relationships
    • Also microbes + parasites, fungal pathogens, etc
  • Agriculture and such – plant microbes, animal microbes
    • And herbivore pests/animal pests and their microbes
  • What do I think: Mutual relationships with microbes not new concept
    • But not often caught in the moment of happening
    • Only 14 generations to evolve relationship
    • Not that long, considering evolutionary time scales
    • Short enough to document in research paper
  • Interesting to study what specifically changed in each
    • Probably in worm, less defenses against microbe
    • What about microbe?
  • Changing environment can cause relationships to develop in new ways
Last modified on Sunday, 14 October 2018 20:44
Jesse Noar

Jesse Noar is microbiologist with a PhD from North Carolina State University and Bachelor's from Cornell. Most of his research has focused on the amazing abilities and potential uses of bacteria, especially those found in soil. Jesse hosts the BacterioFiles podcast highlighting the most interesting recent microbiology research on all kinds of different microbes, part of the ASM family of podcasts. Learn more at or at