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Sunday, 01 October 2017 22:10

Antibiotic Acts As Agreement - BacterioFiles 312

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Published in Bacteriofiles

This episode: Bacteria that produce antibiotic molecule can also use it for communication between cells!

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(10 MB, 11 minutes)

Show notes: 

bf312qsMicrobe of the episode: Rosellinia necatrix victorivirus 1

Journal Paper:
Beyersmann PG, Tomasch J, Son K, Stocker R, Göker M, Wagner-Döbler I, Simon M, Brinkhoff T. 2017. Dual function of tropodithietic acid as antibiotic and signaling molecule in global gene regulation of the probiotic bacterium Phaeobacter inhibens. Sci Rep 7:730.

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Episode outline:

Background: Antibiotics an amazing discovery
Made a lot of modern medicine possible
Much less at mercy of infectious diseases
Surgery not a high-risk undertaking
Penicillin from fungus, but actually many antibiotics come from bacteria themselves
In soil, can use for competition with rivals
Also why resistant microbes not hard to find even before we started overusing
Either from producers resisting their own, or rivals resisting each other
But some antibiotics we make need large amounts to work
Not produced in such large amounts by wild producers in soil
So what is the point of producing at all if not inhibiting rivals?
What’s new: Now, scientists publishing in Scientific Reports have shown that antibiotics can sometimes act as chemical signals for communication between bacteria!
Many bacteria communicate with small molecules called acyl-homoserine lactones
Quorum sensing
Each member of population makes a little, and when enough builds up, reaction
Like group of people raising hands to vote; with large enough “Yea”, go forward
No reason why other molecules couldn’t work the same way
Marine bacterium Phaeobacter inhibens, forms strong biofilms
Produces compound, tropodithietic acid or TDA; works as antibiotic tho not yet in use
P. inhibens considered probiotic in aquaculture and other stuff
TDA production regulated similarly to quorum sensing molecules; induces production of itself
Feedback loop
But does it affect anything else as signaling compound?
Methods: Tested P. inhibens normal quorum sensing system
Uses AHL; each cell produces, and has protein to sense and respond
Knocked out either producer protein or response regulator
Compared to wild-type, ~10% of genome had different expression
No real difference between two knockouts
Then tried adding TDA to see if it could substitute for AHL
At some level, ~1 mM, TDA kills P. inhibens
So added lower conc, only 1.5 uM
Found that TDA restored ~7% of genome to normal; almost the same as wild-type
Subs for AHL
Looked at specific functions regulated
QS downregulates motility and chemotaxis
Confirmed in motility assay
AHL mutants swam more/faster, unless given TDA
Also regulates biofilm formation; QS downregulates
Also upregulates TDA production; as known, TDA increased itself
Summary: TDA not only an antibiotic, but at lower concentrations can act as communication between cells
What do I think: Lots more antibiotics in the world than there used to be
How might they be affecting things in unexpected ways? Even when diluted a lot
Previously have also discovered other antibiotics that can act as signals, and vice versa
Interesting to wonder whether production evolved for one purpose or other
First one, then also coopted for other maybe
Not as costly to use same molecule for multiple purposes
Don't know the mechanism of TDA subbing for AHL, very intriguing
Quorum sensing deficient mutants are like Forever Alone, no cooperation
Might seem weird that signals downregulate both motility and biofilm production
Aren't those kinda opposite behaviors?
But it's like, if swimming around, just seeking place to attach, need biofilm to do so
Once attached, not as much need to maintain; can look for opportunity to disperse
Phaeobacter specifically likes sticking to various marine organisms to ride around
Related: Phaeobacter likes killing algae it's riding on
Portable food source
Toxins used to kill algae are precursors of TDA synthesis
Interesting possible link between molecule effects
The world of microbes is complex and fascinating!

Last modified on Sunday, 01 October 2017 22:17
Jesse Noar

Jesse Noar is microbiologist with a PhD from North Carolina State University and Bachelor's from Cornell. Most of his research has focused on the amazing abilities and potential uses of bacteria, especially those found in soil. Jesse hosts the BacterioFiles podcast highlighting the most interesting recent microbiology research on all kinds of different microbes, part of the ASM family of podcasts. Learn more at or at