Monday, October 15, 2018

BacterioFiles 358 - elegans Endures Edifying Enterococcus

Caenorhabditis elegans
By Bob Goldstein, UNC Chapel Hill
Own work, CC BY-SA 3.0
This episode: Roundworms and not-too-irritating bacteria quickly evolve a beneficial relationship when under threat from other bacterial pathogens!
Download Episode (7.5 MB, 8.1 minutes)

Show notes:
Microbe 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

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