It’s been a while since I did spooky microbiology stories back in 2021. Then, I nerded out about zombie worms that melt away bones and use microbes to help them gain nutrients, vampire bacteria that feast upon other bacteria, and zombie fungi that take over the minds of ants.
But this time, I’m bringing you a different kind of Halloween delight.
Today we’re going to meet bacterial ghosts.
What are bacterial ghosts?
Bacterial ghosts are bacterial cell envelopes devoid of any internal contents (ex: DNA, proteins, etc.). Think of them as empty outer shells of bacteria. They’re being studied as a way to deliver drugs, vaccines, and other substances. Because bacterial surface structures remain intact, there are many other applications in the biomedical world. More on that below.
How are bacterial ghosts made?
Scientists created the first bacterial ghosts in the 1980s when they expressed the lysis gene E in bacteria. This gene codes for a protein that causes a specific type of bacterial cells (Gram-negative bacteria) to release their contents. The lysis protein binds to the inside of the bacterium’s cell wall, which leads to tunnels forming within the membrane. These tunnels then allow the bacterium’s insides to be expelled. To give this process more control, scientists developed cells where they could switch the lysis gene E on and off.
A more recent approach to making ghosts use chemicals, such as sodium hydroxide, sulfuric acid, or hydrochloric acid. Chemicals allow scientists to make bacteria ghosts in a wider range of bacterial cells (including Gram-positive bacteria). These chemicals work by disrupting the bacterial cell membrane so that they release their insides.
What are bacterial ghosts used for?
So many things! Bacteria ghosts can carry many types of molecules, from DNA, RNA, and small compounds, so there are many possibilities. They can:
- Encase drugs within their membranes and deliver them to specific cells or tissues. Scientists have tested this for human applications (ex: delivering cancer drugs) or in agriculture (delivering pesticides).
- Act as a vaccine since they contain intact surface components, but can’t replicate and aren’t pathogenic on their own. For example, to create a vaccine against Your Favorite Bacterium, you’d create a bacterial ghost from Your Favorite Bacterium. In the past, there have been efforts to use bacterial ghosts as a veterinary vaccine and as a vaccine for Vibrio cholerae.
- Deliver vaccine components such as antigens or DNA vaccines. In contrast to the above, this would place antigens or DNA from Your Favorite Bacterium within another bacterial ghost. As an example, the probiotic Lactobacillus casei is currently explored as a delivery vehicle for DNA vaccines.
- Stimulate the immune response. Because bacterial ghosts contain immune stimulating molecules in their membranes (called pathogen-associated molecular patterns), bacterial ghosts can help the immune system mount a more heightened response to vaccines or during other therapies.
And there you have it! A quick summary of bacterial ghosts. While this wasn’t an eerie Halloween/microbiology mash-up, I thought it’s another great example of how microbes can be tweaked for positive impact.
