Monday, June 11, 2018

BacterioFiles 342 - Cyanide Stops Cell Suckers

Chromobacterium growing on agar
This episode: Some bacteria can defend themselves from bacterial predators by producing cyanide!

Thanks to Dr. Robert Mitchell for his contribution!

Download Episode (7.7 MB, 8.4 minutes)

Show notes:
Microbe of the episode: Dyoepsilonpapillomavirus 1

News item

Journal Paper:
Mun W, Kwon H, Im H, Choi SY, Monnappa AK, Mitchell RJ. 2017. Cyanide Production by Chromobacterium piscinae Shields It from Bdellovibrio bacteriovorus HD100 Predation. mBio 8:e01370-17.

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    Episode outline:
    • Background: Predatory bacteria are super cool
      • Like Bdellovibrio bacteriovorus
    • But being targeted isn’t death sentence
      • Some prey can resist, with chemical defenses like indole
      • Or violacein, related to indole
        • Produced by various bacterial species
        • Antibiotic activity, can inhibit bacteria, protists, and roundworms
    • What’s new: Now, Dr. Robert Mitchell and coauthors Wonsik Mun, Heeun Kwon, Hansol Im, Seong Yeol Choi, and Ajay Monnappa, publishing in mBio, have discovered an interesting new way that some bacteria defend themselves from predators!
    • Methods: Bacterium is Chromobacterium piscinae
      • Neat cos grows purple colonies, produces violacein
    • Here is Dr. Mitchell describing the study: statement 3
    • 1st noticed that C. piscinae can resist predation when growing in nutrients
      • But not when deprived of nutrients
      • Seems to be producing and secreting an inhibitor
        • Growth medium could protect E. coli from predation too
    • But then as mentioned, no inhibition after concentrating
      • Despite some amount of violacein present
    • Instead, tested cyanide hypothesis: Chromobacterium produces cyanide
      • C and N with triple bond, binds things more tightly than oxygen, strong oxidizer
        • Targets electron transport chain in respiration, kinda suffocates
      • Cyanide in media correlated well with predation inhibition
      • C. piscinae also has genes for proteins that help it resist cyanide poisoning
      • Adding cyanide to condition without nutrients prevented predation too
    • Prevents predator energy generation, keeps from swimming around
    • Summary: statement 1
    • Applications and implications: statement 2
      • Some Chromobacterium occasionally infects humans, could be relevant to treatment
      • Could maybe modify Bdellovibrio to resist cyanide in that case
    • What do I think: Here’s what the scientists are planning for the future: statement 4
    • Microbes have some pretty clever and interesting ways of surviving
    Author Transcript:
    As you may know, Bdellovibrio bacteriovorus is an obligate predator of other bacteria, entering the periplasm of the prey and consuming them from the inside. The study that we did here looked into the ways that bacterial prey may actually protect themselves from bacterial predation. And what we found was cyanogenic bacteria, meaning those that produce cyanide, can actually be resistant under the right conditions.

    The overarching goal of our research is to evaluate the use of predation as a means to reduce and remove pathogens. In effect, we hope that we can use these in the future as living antibiotics. The work here shows prey factors may actually hinder the activity of the predators, including Bdellovibrio bacteriovorus, although the number of cyanogenic bacterial species that have been identified is not that large, it is a factor that may need consideration downstream when we try to apply them.

    When we were trying to identify the factor responsible for the inhibition, we initially thought that it had to be violacein, the antibiotic that's produced by different strains of Chromobacterium. To test this, we chose to concentrate the media using an evaporator, with the expectation that the higher concentration of the antibiotic would make it more inhibitory. But unexpectedly, the media was no longer blocking predation. This suggested to us at the time that one, violacein was not responsible, and two, that the true effector must be volatile. Wonsik, being a great scientist that he is, scoured the literature and found several very old papers talking about Chromobacterium also being cyanogenic, leading to the results that we presented within our paper.

    We are currently evaluating other prey factors and their importance. We have also expanded to study abiotic factors and their impacts. Again, with the goal of understanding how different environments and conditions modulate or change the activity of the predators.

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