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Bacteria produce colourful antibiotics to protect frogs

Microbial communities grow everywhere and on almost any host, be it humans, plants or animals.

And while some microbes come to make their hosts sick, other mirobes are there to help and protect them.

This is a story of both types of microbes and an unusual host: amphibians.

Yes, also frogs and salamanders and other amphibians carry microbes on their skin.

And some of these microbes are meant to kill the animals. But, luckily, the animals are protected by helpful bacteria that produce antibiotics.

Read on to find out how bacteria and fungi do not get along on the skin of amphibians and how bacteria could even protect amphibians from extinction.

About fungi that infect the skins of their hosts

Many frogs, salamanders and other amphibians already went extinct because of a deadly fungal infection. And it seems that many more animals are already infected and sick from that same pathogen.

The bad guys? The two fungal species Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans. They cause a deadly skin disease on frogs and other exotic amphibians.

Similarly, the fungus Trichophyton rubrum can infect our skin and hair. This pathogen causes a disease that you may know as ringworm or athlete’s foot. Typically, you can see such a fungal infection as a red, itchy and circular rash.

But luckily there is a new weapon around to keep these fungal intruders at bay: Bacteria that get rid of the fungus to protect their hosts.

Janthinobacterium lividum kills pathogenic fungi

Few microbes can grow and thrive on the gloomy skin of frogs or salamanders. One such microbe is the bacterium Janthinobacterium lividum.

This bacterium eats the mucus of the amphibians or part of the skin when they shed their skins. But they also help the amphibian in case the deadly fungus shows up.

Generally, bacteria produce antibiotics to get rid of annoying competitors. So, for example, Janthinobacterium produces the antibiotic violacein, which has a dark violet colour. This antibiotic kills the fungus, so it will not make the frog sick.

Researchers still don’t know how Janthinobacterium transports the antibiotic to the fungus. But in Bacteria firing toxic bubbles, we saw that the bacterium Chromobacterium violaceum throws membrane bubbles filled with violacein at its competitors. So, Janthinobacterium might use a similar strategy and throw violacein bubbles at the fungus.

Janthinobacterium lividum lives on frogs and protects them from pathogenic fungal species
Janthinobacterium lividum kills pathogenic fungi on frogs. By Noémie Matthey.

Also, when Janthinobacterium grows on the skin of frogs, it triggers the frog to produce other anti-fungal molecules. These molecules kill the fungus and other pathogenic bacteria that are not helpful to the frog.

More bacteria protect from deadly fungi

Janthinobacterium is not the only bacterium that produces colourful antibiotics to protect its host.

You might have seen red dots in your shower every once in a while. These come from the bacterium Serratia marcescens that makes a red antibiotic. This bacterium also lives on the skins of amphibians and the red antibiotic protects from deadly fungi.

Also, allrounder bacteria from the Pseudomonas species live on the skins of some amphibians. And these bacteria produce many different antifungals.

Hence, it looks as if the right skin bacteria protect frogs and salamanders from deadly fungi. And these bacteria keep throwing around colourful bubbles filled with antibiotics – sounds like a bacterial festival that celebrates their host?

Saving amphibians with bacterial Janthinobacterium communities

Now researchers are trying to save the amphibians from the deadly fungus with a process called bioaugmentation. With this strategy, researchers introduce special bacterial communities to the environment. And they hope that the bacteria will jump over to different amphibians.

Bacteria like Janthinobacterium then hopefully establish stable communities on the skins of amphibians and protect them from fungal infections. And let’s hope that these bacterial parties will save more cool frog species from extinction!

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