Bacteria inside Shoes

Bacteria inside Shoes


They are hardly a topic discussed very often. Yet there are many bacteria living inside your shoes. There they can result in smelly shoes which are an annoyance to yourself and anyone who comes close to them.

In this blog post, I will give you short information on bacteria inside shoes: where they come from, what kinds of bacteria may live inside your shoes and how to limit the impact of such microorganisms living in your shoes.

Where do the bacteria in your shoes come from?

This is pretty straight forward. On your skin live many different bacteria. Most of them play helpful roles for your overall well-being. They create a biological environment harmful to pathogenic microorganisms. However, some bugs on your skin also are less positive for you. Apart from real pathogens, there are bacteria that are not making you sick but are still annoying.

They break down the contents of your sweat and transform them into smelly compounds (e.g. butyric acid). One of the areas where this happens commonly is your feet.  I am sure that you are familiar with the typical smell of “cheesy feet” that have stuck in shoes for a couple of hours and sweated a lot in those shoes.

Apart from the smelly particles from your feet that go directly into your socks and shoes also some of the bacteria from your feet get transferred into your shoes, together with some more sweat. This sweat they can degrade as well, creating your very own “Cheese Factory”. Yuck..

What kind of bacteria live inside your shoes?

Typically the bacteria in your shoes are the same that can be found on your body causing all kinds of smells. Examples of bacteria strains that live on the skin and create the typical cheesy smell are:

  • Brevibacterium epidermis
  • Staphylococcus spp
  • Bacillus subtilis natto

What to do against smelly shoes?

Here are some tricks against the bacteria living on your feet and inside your shoes and the smell they can create (some are pretty obvious):

  • Wash your feet every day, and whenever they are smelling
  • Change your socks often
  • Don’t wear the same pair of shoes all the time. Rather rotate them every day.
  • During the day go barefoot or at least without shoes as often as you can (i.e. do not wear them at home or in the office).
  • Wear sandals
  • When your shoes smell and you can wash them, do so.
  • Use deodorants inside your shoes, such as sprays or deodorant balls.
  • Use sprays that kill off microorganisms, such as silver solutions.

All pretty simple things that should keep your feet and shoes smell-free and reduce the number of foot odor bacteria.

Cupriavidus metallidurans and Delftia acidovorans gold bugs

Have you heard of Cupravidius metallidurans and Delftia acidovorans?

Cupravidius metallidurans and Delftia acidovorus truly are real gold bugs – gold producing or gold mining bacteria.

Cupriavidus metallidurans and Delftia acidovorans
Meet the real Gold Bugs

Let me show you how those two bacteria are able to create gold deposits like miniature miners.

Cupravidius metallidurans

The bacteria Cupriavidus metallidurans lives in soils that have high concentrations of metals such as gold, or copper in them. For most other bacteria such metal-laden soils are highly toxic. They cannot grow and reproduce there.

Cupravidius metallidurans on the contrary has developed the ability to withstand the effects of toxic metals. The bacterium does this through changing the toxic soluble forms of heavy metals into non-solubable forms of metals. The non-solubable form of gold is….a gold nugget.

Thus, this gold mining bacterium produces pure gold from the heavy metal waste containing gold chloride (the soluble gold). In nature it plays a key role in creating so-called secondary gold deposits (primary deposits are original ancient geological formations of gold ores).

How exactly Cupravidius metallidurans achieves this feat was discovered by a joint research team from Australia and Germany in 2018.  If you check out the link you can also see nice pictures of the bacteria and the gold they produced.

Delftia acidovorans

Cupravidius metallidurans‘ “colleague” Delftia acidovorans uses means similar to the ones used by the former gold digger. However, while Cupravidius metallidurans forms the insoluble gold through mechanisms inside the cell Delftia acidovorans secrets a substance that binds the soluble gold toxic to bacteria outside the cell. The substance thus turns it into harmless mineralized pure solid gold.

Scientists who discovered the gold digging microbe’s ability to secret a substance to bind gold outside the cell named the substance delftibactin.

So there you have it. By just defending themselves against the toxic effects of heavy metals Cupravidius metallidurans and Delftia acidovorans have arguably become the first real and original gold bugs ??.

Would you like to have a fermenter full of these microminers at home or rather some gold bug shares (i.e. shares in gold mining companies)?


Cocoa Fermentation – The road to great cocoa and chocolate

Cocoa Fermentation – What is that?

Did you know that your cocoa and chocolate is made by tiny microorganisms in a process called cocoa fermentation?

Yes, it is true: the best cocoa and most chocolates are produced by fermentation of the cocoa beans. But let me start right at the beginning: Let’s go and see where your hot chocolate and chocolate bars come from.

Harvesting Cocoa Beans

Cocoa trees stem from South  and Central American rainforests. However, nowadays they are grown in various tropical locations worldwide. They start bearing cocoa fruits when they are three to four years old. Throughout the year they produce white and pink flowers. Only some of those flowers develop into cocoa fruits. These are also called cocoa pods. In the end one tree only produced around 20 to 30 fruits per year.

Or in other words: It takes one tree to produce about 500 grams of chocolate. The actual amount of chocolate one can make depends on the content of cocoa in the chocolate. For example, milk chocolate has less cocoa content than dark chocolate.

The cocoa pod and beans

A cocoa pod ripe for harvest has a yellow-orange color. It takes up to 6 months for a cocoa flower to develop into a ripe cocoa pod. When the pod is opened one can find a sweet white pulp. In the pulp there is what you are looking for: the actual cocoa beans. There are between 30 and 50 cocoa beans in a fruit. Their color ranges from a pale lavender to dark purple.

The leathery rind of the pod is discarded and the cocoa beans together with the surrounding white pulp are kept to be processed into great cocoa.

Cocoa Fermentation – The magic of chocolate making

Cocoa seeds have a strong, bitter taste. If you tried them you would not like them. At this point comes the magic. Our friends, the tiny microorganisms make the cocoa beans taste better through the process of cocoa fermentation.

cocoa fermentation
                  cocoa fermenting microorganisms – bacteria and yeasts

Fermentation is the work of yeasts, as well as of acetic and lactic acid bacteria. Here is what they do in a nutshell:

Yeasts make alcohol from the cocoa pulp. The bacteria convert the alcohol to lactic and acetic acid. At the same time through the bacterias´ actions the temperature rises. All these activities kill the cocoa bean and also alter the bean chemically. The end result is a cocoa bean as you know it: brown and with the typical chocolate flavour.

The cocoa producers call this process “sweating”: The seeds and pulp are heaped into piles and left for the bacteria and yeasts to do their work. The microorganisms ferment the beans and the pulp, which is liquefied as it ferments.

The fermented pulp over time trickles away. Left behind are the fermented cocoa beans. This process takes about 2 to 5 days.

Finally the cocoa beans are collected and dried. They are now ready to be made into cocoa powder, drinking chocolate, chocolate bars, and all the other chocolaty things you like so much.

To learn more about cocoa and cocoa beans have a look here.

Christmas Trees and Mycorrhizal Fungi

Mycorrhizal Fungi – How a little Fungus helps grow your Christmas tree as well as other plants.

Christmas tree and mycorrhizal fungus
Christmas tree and mycorrhizal fungus (magnified)


Can you believe that a microscopically small mesh of fungi is responsible for providing you with the Christmas tree that makes your winter holiday season just perfect?

Pines, firs, Douglas firs, and spruces are the trees most commonly used as Christmas trees. All of them harbor a secret you probably have not heard about yet. They depend on a network of fungi called mycorrhiza that acts as an extension to their roots. The mycorrhizal fungi provide the trees with additional nutrients that the trees could not efficiently get on their own.  They also make the intake of water easier for the tree.

In return the plant provides the fungus with sugar created by the tree through the use of light energy in a process called photosynthesis. This mutually beneficial relationship is another example for a symbiosis, as described before.

The mycorrhizal fungi also form fruiting bodies – mushrooms, many of which are edible.

Mycorrhizal Fungi everywhere

Mycorrhiza is almost everywhere in a healthy forest. It is believed that up to 90% of all trees are living in symbiosis with a mycorrhizal fungus. Without those fungal friends, most trees would not grow properly and stay small and weak. They would also be more vulnerable to diseases.

Some mycorrhizal fungi live in symbiosis only with a particular kind of tree; others form mutually beneficial relationships with various kinds of trees.

The two types of Mycorrhizal Fungi

There are two known main types of mycorrhiza that differ in the way they interact with the trees’ roots.

Endomycorrhizal fungi grow into the membrane of the cell of the tree’s root.

Ectomycorrhizal fungi form a sheet surrounding the root of the tree they live with. However, they usually do not grow into the cells of the tree’s root. There are some exceptions to this rule. Ectomycorrhizae are the ones associated with Christmas trees.

So next time you sing a Christmas carol under the Christmas tree think about the fact that you would not have a nice tree without the tiny fungal net called mycorrhiza.


The Christmas Wreath Lichen – Cryptothecia rubrocincta

Did you know that there is a lichen named after Christmas? Here comes Cryptothecia rubrocincta – the Christmas wreath lichen.

Christmas Wreath Lichen
The Christmas Wreath Lichen – Cryptothecia rubrocincta

Cryptothecia rubrocincta, commonly called Christmas wreath lichen, grows on the barks of trees, and rarely on stones. It lives in the southeastern USA, central- and South America. It has also been found in some areas of Africa.

What makes this lichen so spectacularly different to any other lichen is its pattern of red and green colors that give the impression of a Christmas wreath – hence its name. In contrast, most other lichens are of light to dark green or blue-green color, grey, brown or black.

The red pigment of the Christmas wreath lichen is called chiodectonic acid. It protects the lichen against the negative effects of ultraviolet light from the sun. The red color can be extracted from the lichen and used as a red dye.

If you are not quite sure what a lichen is, have a look below.

Lichens – The basics

Lichens, such as the Christmas wreath lichen Cryptothecia rubrocincta, represent a symbiotic community between a fungus and algae or cyanobacteria.

Symbiosis means that two or more organisms live together and each of the partners in the relationship gets an advantage out of it.

In the case of lichen, the algae or cyanobacteria are responsible for producing nutritious sugars through the power of captured sunlight (photosynthesis). The fungus provides additional nutrients. It also serves as a protective mesh for its symbionts. In addition, the fungal mesh retains water needed by the algae and cyanobacteria.

Lichens under a microscope: A symbiosis between a fungal mesh (white) and algae or cyanobacteria (green globes).

Lichens are very robust and usually among the first organisms colonizing hardly habitable rocky areas.

Another interesting fact related to Christmas: Some kinds of lichen are the main food source in winter for reindeer.

So Rudolph likes them as comfort food during wintertimes. However, it is not known, if he also eats Christmas wreath lichens when he comes to South America ;0).

For further information on the Christmas wreath lichen Cryptothecia rubrocincta and some great photographs on the real deal go to

Germs Cartoon Pics and Educational Content for Kids and Adults!

GermToons – A New Site on Germs for Children and Adults

Today we are very excited to provide you with great content on germs for kids accompanied by germs cartoon pics. Germtoons was started by Alexander Matis, a father of three and MSc in Molecular Genetics. We aim at educating kids and adults in a fun and informative way about the exciting world of micro-organisms. Learn all about bacteria, viruses, fungi and protozoa.

Germs Cartoon Pics and much more

Over the next couple of weeks, months and years GermToons will provide articles and blog posts about germs. We will also cover famous people who research(ed) them.  The articles will be spiced up by germs cartoon pics. In addition, we will provide educational resources such as books, videos, experiments and useful products for teaching your kid, our yourself, about micro-organisms.

Join the GermToons Community!

If you have any particular germ-related topic that you would like to learn more about, please get in touch. We will work on publishing it. Also, join our newsletter to get updates on new posts and articles. By joining our newsletter, you will get free access to my new Ebook: “Bacteria – An Educational FunBook for Kids and Adults” (also available as a hardcover on Amazon).

Finally, if you would like to work with us or to use any of the illustrations on this site please also get in touch with a.matis(@) You can also use our contact form.