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| Anabaena flos-aquae, a source for gas vesicle genes |
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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