Spores: Extreme Survivors

Written by Lucy Eland, Edited by Nicola Simcock

Have you heard about the 40 million-year-old bacteria that survived inside the abdomen of a bee, preserved in a chunk of amber? Amazingly, when removed from their amber tomb and given nutrients, the bacteria were still able to grow! Our speaker this month, postgraduate researcher, Clare Willis, from Newcastle University’s Centre for Bacterial Cell Biology, explained how this is possible.

When conditions become extreme, some bacteria create an ‘escape capsule’ that allows them to survive in an inactive state, until the environment becomes more favourable. This ‘escape capsule’ is known as a spore and contains all the bacteria’s genetic material packaged up into a hardy capsule, that protects it from damage. Clare explained to the captivated audience that this spore state can be problematic for humans. Many bacteria, known for their antibiotic resistance in hospitals, such as Clostridium difficile, can make spores that are difficult to destroy. Anthrax infections and botulism are also caused by spore-forming bacteria. These spores can lie dormant and undetected, before flaring up rapidly and causing serious infections.

Making a spore

Infographic showing how a spore forms within a bacterial cell once the bacterial DNA has been duplicated. 

Clare’s research for her PhD looked at how spores are created, which could offer valuable insights into how spore-forming bacteria can be controlled. Under normal replication conditions bacterial cells split in half to make two copies, each containing one complete set of DNA. When the environment becomes uninhabitable and a bacterial cell ‘decides’ to make a spore, the DNA is copied as usual, but the cell separates into a smaller cell (‘prespore’) and a larger one (the ‘mother cell’). This means that one copy of the DNA must move across the dividing cell into the prespore. Clare’s work looked at how this happens ─ with the aid of fluorescent tags stuck onto the DNA. These tags allowed her to study the movement of the DNA with a microscope, by tracking the fluorescent colours. Once she tagged the DNA she found something surprising ─ both DNA copies moved towards the prespore, not just one. This led her to think that the two DNA copies must be attached together in some way. Clare carefully considered and assessed four different ways the DNA could be connected. Her favourite theory, most supported by the evidence, is that the two copies of DNA are held together by proteins. Clare hopes to do further work to find out more about these proteins and thus better understand how spores form.

Spore formation microscopy

Fluorescence microscopy pictures by Clare Willis and a supporting diagram to show how both copies of DNA within a bacterial cell move together toward the ‘prespore’ when packaging DNA into a spore. A particular region on the DNA is labelled in red and the outside of the cell is labelled in green. Each picture is taken 15 minutes apart.

After recharging our glasses, there was much discussion and lots of questions from the audience:

What happens to the mother cell after the spore is formed? It bursts and dies!

How long does it take to make a spore? Longer than normal cell division, as the spore needs to be coated in proteins before it can emerge from the mother cell, usually a few hours.

Do all bacteria in a community make the same ‘decision’ about when to make a spore? A population of spore-forming bacteria will differ in the timing of spore production, depending on how each cell senses and responds to environmental changes.

And how long does it take a spore to ‘germinate’ and start growing again? Depending on the species, bacteria can emerge from the spore within hours of exposure to a suitable environment and nutrients.

Clare’s excellent talk gave us all a great introduction to the wonderful, microscopic world of bacteria and one of their most extreme survival mechanisms.

We look forward to seeing you at the next SciBar event on Wednesday 21st of November where we will hear Riona Mc Ardle’s talk ‘What can walking tell us about dementia?

 

 

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