Monday, November 20, 2017

BacterioFiles 318 - Killers Controlling Coral Contamination

Predator attacking and killing prey
From: Welsh et al. 2017 PeerJ
CC-BY 4.0
This episode: Bacteria that prey on other bacteria could help keep corals healthy! Thanks to Rory Welsh for his contribution.

Download Episode (12.8 MB, 14 minutes)

Show notes:
Microbe of the episode: Latino mammarenavirus

Journal Paper:
Welsh RM, Rosales SM, Zaneveld JR, Payet JP, McMinds R, Hubbs SL, Thurber RLV. 2017. Alien vs. predator: bacterial challenge alters coral microbiomes unless controlled by Halobacteriovorax predators. PeerJ 5:e3315.

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    Episode outline:

    • Background: Corals having a lot of problems
      • Toxins, global warming, disease
      • Some areas in Caribbean lost 80%
    • Disease-causing bacteria such as Vibrio species
      • V. cholerae causes disease in humans, and V. coralliilyticus in coral
      • And warm temps make it even more disease-causing
      • Then other opportunists come in to make things worse
    • But corals also symbiotic with other microbes that can be helpful
      • Photosynthetic dinoflagellates Symbiodinium live in coral cells
      • Some bacteria might help with nitrogen metabolism
      • And some might help defend against pathogens
    • Statement 1
    • What’s new: Now, scientists publishing in PeerJ have shown how bacteria that prey upon other bacteria help keep coral symbiotic communities stable and healthy when challenged by pathogens!
    • Predatory bacteria are Halobacteriovorax
      • Statement 2
      • Similar to Bdellovibrio
      • Act like xenomorph in Alien, infect host and then consume from within
      • Thus the title, Alien vs. Predator
        • Predator is Halobacteriovorax, alien is Vibrio cos foreign to coral
    • Statement 5
    • Methods: First tested to see if Halo feeds on relevant pathogens
      • Plaque assays on agar
      • Feeds on various Vibrios, but not all
      • Some strains of V. coralliilyticus, also V. cholerae
    • Then tested effects of bacteria on coral, Montastraea cavernosa
      • Great star coral, makes big mounds over 5 feet in diameter
      • Got samples from Florida Keys National Marine Sanctuary, divided into separate chambers
    • Analyzed coral microbiomes by sequencing
      • Normal, challenged by V. coralliilyticus, and alien + predator
      • With just alien, microbe diversity increased
      • With predator also, diversity did not change
      • In many places a good thing, but not if increase is opportunistic pathogens
        • Saw increases in orders known to have opportunists, Rhodobacterales and Cytophagales
    • Summary: Invader bacteria like Vibrios can disrupt coral health and allow disease, especially at higher temps. Predators can prevent microbiome disruption and possibly prevent disease
    • Applications and implications: Better understanding of coral health
      • Very important to health and beauty of oceans
    • Statement 3
    • Statement 4
    • Maybe consider using predator directly, but tricky
      • Have to know disease is happening and then inoculate?
      • Predators might not stick around for too long before or after disease
      • Big areas to monitor and cover
    • Thought predators would also be useful for reducing numbers of other problems, like cholera
    • Clarifications if necessary: Not clear still if V. coralliilyticus infects this coral, M. cavernosa
      • But definitely infects others, and here causes microbe disruptions that could be problem
    • What do I think: Not so simple as pathogen vs. victim
      • Even if Vibrio here doesn’t infect directly, can allow others to infect by disrupting health
    • And even if predator doesn’t attack actual pathogens directly, prevents disease?
      • Good to think about that regarding our health etc
      • preventing susceptibility instead of directly killing agent
        • Oz of prevention etc
    • At least in this case, predator wins!

    And the rationale for this work is that, despite all the recent research showing the importance of a host microbiome for the host health, the ability to respond to stress, to fend off diseases, there's a lot less known about what are the actual drivers that support a steady, stable host microbiome, or can contribute to changes. We have a lot of other evidence coming out showing that those host microbiomes dramatically change as the host goes from a healthy to a diseased state, but again a lot less is known about what are the drivers that contribute to stability or to potentially disrupt that microbiome.

    And our previous work showed that the predator that we used in this study was consistently associated with corals, and we know from macroecology that predators play an outsized role in shaping their communities. There's examples such as in terrestrial systems, the reintroduction of wolves into Yellowstone and the cascading effects there, as well as in aquatic systems the importance of sea otters and grazing on urchins for the kelp forest.

    I think this research is an exciting first step towards understanding how basic ecological principles such as predator-prey dynamics contribute to the structure and function of a host microbiome. Researchers now have the tools, thanks to metagenomics and advanced molecular detection, to look at community-wide changes in a microbiome, and test foundational aspects of ecology, all on a living host system. And that's pretty cool.

    corals are inherently hard to work with. What I'd like to see this work followed up by is using a well-defined model system like the nematode or fruit fly models and using truly quantitative methods to study how these predator-prey interactions are shaping the structure and function of host microbiomes. And also look at the host side of these changes and bacterial challenges.

    when it comes to coming up with a title for your research, it's always difficult to summarize sometimes months or years of work in just a few words, and when this Alien vs. Predator was floated out there, we all just loved it, I mean it's so perfect, if anybody's seen the movie, you know that these are two formidable species that have all sorts of tricks up their sleeves, and here in this study, our bacterial predators are the smallest, nastiest bacteria that exist in the microbiome, I mean, these predatory bacteria must actively seek out, attach to other gram-negative bacteria, burrow inside and seal their point of entry in order to grow and replicate, wearing their host as a kind of skin in stealth mode before bursting out and doing it all over again. On the other end of the spectrum, we have the invading alien pathogenic bacteria that has all sorts of virulence factors and hydrolytic enzymes that enable it to cause pretty devastating diseases for the corals. So I loved the name, submitted it, thinking the reviewers were never gonna let it slide, but not only did the reviewers not mention or suggest changing the title, they totally bought into it and referred to the bacterial challenge as aliens and predators in their comments and reviews. So the name stuck, and I have a chapter in my dissertation titled "Alien vs. Predators", and all of us can now say that we have an article in a scientific journal titled Alien Vs. Predators.

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