One Type of Soil Bacteria Performs Two Important Jobs to Help Us Produce Healthy Food

Although they are small, bacteria perform some very important jobs that help us make healthy food. Food production starts with growing plants out in the field. Here, bacteria that live in the soil help plants to grow strong and tall, and they can even protect plants from some diseases. This way, the bacteria are helping the plants to stay healthy and they are helping the farmer to grow lots of food without using too much pesticide. After harvest, bacteria do even more work to make food that is tasty and good for your health, by making fermented superfoods like kimchi, kombucha, and natto. An example of a bacterium that can do both of these jobs is called Bacillus subtilis natto, and we have investigated what makes it such a useful and important species. We found that the natto bacterium produces important enzymes that can attack fungi that would cause plant disease.


WHAT IS "BIOCONTROL"?
The tiny bacteria that live in the soil can do a huge number of important jobs that help us to make nutritious and healthy food in a way that does not damage the environment. Some soil bacteria can protect crops like the soybean plant from diseases by fighting o the fungi that might cause an infection. We use the term biocontrol when we are BIOCONTROL The use of living organisms to control plant diseases, instead of using chemical pesticides. An example is using bacteria to control fungi that can damage plants.
using a living organism to protect our food. You can think of examples of biocontrol like using cats to keep rats away from food, or using ladybirds to eat aphids that can damage crops. Biocontrol helps us limit the growth of harmful organisms without using chemical pesticides. Pesticides can have lots of harmful e ects on the environment, such as killing o the insects that pollinate plants and killing the microbes that keep plants healthy.
In our work, we are studying how bacteria can control the growth of fungi that would cause disease in crop plants. Normally, farmers use chemical pesticides to control these fungi, but many fungi are becoming resistant to the pesticides and are no longer a ected by them, so they are getting harder to control. This means that farmers use more and more pesticide, causing more ecological damage, and making resistance spread even more! Using soil bacteria for biocontrol of fungi means that farmers can use less chemical pesticide on the fields where crop plants are growing. Using less pesticide is good for the soil, the air, the water, and for the insects that pollinate our plants, so these bacteria are protecting the whole environment, as well as helping us to grow food.

THE NATTO BACTERIUM IS A SUPER-FERMENTER!
After we harvest food from the field, sometimes it goes through processes in a factory to make it into something that is ready to eat, and soil bacteria are often used in these processes. In fact, many of the tools that bacteria use in food production are very similar to the tools other bacterial species use in the soil to control fungi. One bacterial species-Bacillus subtilis natto-can do both of these things! The natto bacterium is part of the Bacillus group of species that are found in soils all around the world. This bacterium has been used for a very long time in Japan to make a food that is also called natto. This food is made when the natto bacterium turns soybeans into a sticky-and stinky-food substance, through a process called fermentation. Natto is very popular in Japan, where it is a common FERMENTATION A process by which microbes break down certain foods using enzymes, to turn the food into a di erent kind of substance. Common fermentation products include beer and yogurt. snack and breakfast food, and it is eaten with mustard and soy sauce. In fact, natto has been produced as food in Japan using Bacillus subtilis natto fermentation since the Taisho period, just after the First World War. The natto bacterium is also an icon of popular culture in Japan-one of the characters in the manga comic book and anime series called Moyasimon: Tales of Agriculture is a cute bacterium called kids.frontiersin.org October | Volume | Article | Natto. His job on the farm is to ferment soybeans to make the natto for the human characters to eat.
It is also becoming quite fashionable to eat natto in the rest of the world, because now we know that fermented foods are very good for human health [ ]. Many fermented foods and drinks are now available in shops, including kombucha tea, kimchi pickles, tempeh, and yogurt, and all of these foods can help our digestion. Natto is high in fiber and contains a lot of vitamin K, which we need to grow strong and healthy bones. By fermenting soybeans into natto, our natto bacteria are making a tasty snack that is great for your tummy and your whole body!

HOW DOES NATTO CONTROL THE FUNGI THAT WOULD CAUSE PLANT DISEASES?
Thanks to a recent project I was involved in, we now also know that our natto bacteria are probably making a big contribution to preventing fungal disease in some plants. The natto bacterium shows many of the important behaviors that we see in other plant-protecting bacteria.
In particular, the natto bacterium can very e ectively attack the cell wall that protects fungal cells [ ]. Fungi, like the ones that can cause disease in soybean plants, have long, thin cells that grow quickly by extending one edge of the cell forwards in one direction, forming thin strands called filaments. These cells have a strong outer layer-called the fungal cell wall-that is partly made up of a material called chitin CHITIN A very strong polysaccharide found in the walls of fungal cells, which protects the cells from the environment and helps fungi to infect plant cells.
( Figure ). Chitin is a polysaccharide, which is a very long molecule POLYSACCHARIDE A long chain of sugar molecules connected by strong chemical bonds. For example, cellulose is made of long chains of the sugar glucose. Chitin is a polysaccharide made by fungi.
made up of lots of smaller sugar molecules joined together, and it is rigid and very strong. It acts like a suit of armor, protecting the fungal cell from the environment and from attack by other microbes. It also makes the fungal cell strong enough to break into plant tissue, which is how plant infection often begins.
Enzymes that can break down chitin into small pieces are therefore a ENZYME very powerful weapon against fungi, because they damage the suit of armor, and let the fungal cell be exposed and killed. Plant-protecting bacteria in the soil produce enzymes called chitinases that can protect  Figure The fungal cell wall is the strong layer on the outside of a fungal cell that protects the cells from being killed. If the cell wall is broken, the fungus will die, and it will not be able to infect plants. cell walls when these clumps were incubated with the enzymes.
However, we were surprised to see that the natto bacterium does not like to feed on chitin itself, and it will not produce chitinase enzymes if chitin is the only material it can find. Instead, the natto bacterium needs to find a complete fungal cell wall before it will produce chitinase enzymes.

WHAT COMES NEXT IN OUR RESEARCH?
Our results tell us that the natto bacterium can somehow sense when there is fungus in the local environment, and start producing powerful chitinase enzymes to break down the strongest parts of the fungal cell wall. Our results also tell us that we might be able to increase biocontrol behavior in Bacillus subtilis natto by mixing cell walls from dead fungus into the soil. Other researchers have shown that, for other bacteria, adding only chitin to the soil can cause an increase in chitinase production [ ]. But for our natto bacterium, the story is more complicated.
In our tests, Bacillus subtilis natto also produced enzymes that break down protein, which is another important component in the fungal cell wall (Figure ). I was excited by this, because these are the same enzymes that are used in the production of natto as food! The protein-degrading enzymes have been known for a long time, but now we have seen a whole new use for them.
We are now doing some extra experiments to test whether our methods for increasing chitinase production can increase the  Figure We grew cultures of Bacillus subtilis natto and treated them by adding either chitin, whole dead fungal cells, or fungal cell walls from dead fungus cells. Then we measured how much chitinase activity was produced by the bacterium in each treatment condition. You can clearly see that treating with chitin did not cause more chitinase activity to be produced, but treatment with fungal cells or fungal cell wall had a big impact.
biocontrol ability of Bacillus subtilis natto and make it more e ective at killing o the fungi that might harm plants. So far it looks quite promising, and we can see that several of the fungi we have tested are strongly a ected by our natto bacterium. This means that Natto character from Moyasimon anime is actually performing two fantastic jobs on the farm and helping us in two di erent ways to have a good supply of healthy food!

CONFLICT OF INTEREST:
The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

COPYRIGHT ©
McKee. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

KAVIN, AGE:
There are important and interesting things in science.

ROHIT, AGE:
My hobby is drawing and doing science projects. I want to do animated cartoons. My favorite sport is Cricket. I know the capitals and flags of all the countries. I also know some of the major inventions and their inventor's names.

SWATI, AGE:
The article was very informative. It was very interesting to learn about the natto bacterium. The words in the text were easy to understand. My time was spent useful during this quarantine.

LAUREN S. MCKEE
Lauren grew up in the North East of England and is currently living and working in Stockholm, Sweden. She studies bacterial biochemistry and the ways that di erent microbial species can interact with each other and their environment. She works in the lab and teaches students about microorganisms and how they can be used in industry. She is most interested in the enzymes that bacteria produce in the soil-these are very important in natural ecosystems and are also very valuable tools for the biotechnology industry. *mckee@kth.se