Monday, July 2, 2018

BacterioFiles 345 - Super Sonic Cell Sacs

Anabaena flos-aquae,
a source for gas vesicle genes
This episode: Protein bags of gas in bacteria could help make ultrasound imaging more versatile!

Download Episode (7.6 MB, 8.25 minutes)

Show notes:
Microbe of the episode: Cronobacter virus Esp2949-1

News item

Journal Paper:
Bourdeau RW, Lee-Gosselin A, Lakshmanan A, Farhadi A, Kumar SR, Nety SP, Shapiro MG. 2018. Acoustic reporter genes for noninvasive imaging of microorganisms in mammalian hosts. Nature 553:86–90.

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    Episode outline:
    • Background: Microbes have many interesting abilities
      • Try lots of different approaches to adapt to environment
    • One example: gas vesicles in water dwellers
      • Protein sacs that let air in/out but not liquid
      • Fill up with gas to increase buoyancy and float up
      • Easier than swimming; automatic directionality
      • Can regulate oxygen or light exposure
    • What’s new: Now, scientists publishing in Nature have discovered that these gas vesicles can be used in a medical setting: to improve the versatility of ultrasound imaging!
    • Vesicles scatter sound waves better than other things
      • Show up as higher contrast on ultrasound
    • Methods: Engineered Escherichia coli to produce gas vesicles
      • About 100 per cell, ~10% of volume
      • Not enough to generate buoyancy, except for a few
    • Tested with ultrasound pulses
      • Showed good contrast
      • When pressure applied to burst the vesicles, contrast went away
      • Some other engineered cells not optimized for right vesicle size also didn’t show contrast
    • Concentrations of cells from 50 million to 1 billion per mL gave increasing signal
      • Could increase signal even more using only especially buoyant cells
    • Also tried using as a reporter
      • Put vesicle production under control of inducible promoter
      • Added certain chemical, IPTG, cells sensed and produced vesicles
    • Can modify in various ways as needed
      • Number, pressure required to collapse, induction
    • Final test: in vivo
      • Put in mice, in gut
      • Allowed very localized imaging
      • Compared with bioluminescent bacteria, which just showed up somewhere in abdomen
    • Summary: Bacteria producing gas-filled vesicles can be used to improve ultrasound imaging in the body
    • Applications and implications: Could target bacteria to particular place in body to image
      • Cancer, for example, with strains that go selectively to tumors
      • Or particular location where something is sensed
        • Induce vesicle production only there
      • Various creative options
    • Some improvement seems possible with more engineering
    • Could be good for research too, in animals or other places where light doesn't pass through well
    • What do I think: Gotta make sure strain does what we want and not other unwanted stuff
    • But useful to have different options for imaging/diagnostics
      • Fluorescence and bioluminescence have their place
      • But sometimes not enough
    • Clever use of clever microbe environment strategy

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