DNA is everywhere

Wherever you go and whatever you do, you leave traces of DNA behind. DNA is part of the 500 million or so skin cells that you shed every single day. It's also inside the tiny droplets of saliva that you spray into the air when you talk, sneeze, or cough, and it should come as no surprise that there's DNA in your urine and stool, too. So, despite the forensic uses of DNA that we leave everywhere , it can also be used to detect disease outbreaks and local application of substances from wastewater monitoring .

In our microbiome tests, we also examine how much DNA your sample contains, but most of the fecal DNA is not your own DNA!

It is actually a mixture of DNA from different sources. Most of it belongs to bacteria, but there may also be small fractions of DNA from archaea, fungi, viruses, unicellular or multicellular eukaryotes, as well as your own human DNA.

What can you expect from your relative levels of bacterial DNA from your test?

Bacteria are the main component of the gut microbiome. They are small compared to human cells, but their numbers in the colon alone are roughly equivalent to all the cells in your body . Therefore, we expect to see high relative amounts of bacterial DNA.

In our healthy reference group, which you are compared to in our microbiome test, we are able to assign 70% of the DNA to bacteria, while slightly less than 30% cannot be assigned with sufficient certainty.

In science, several conditions are associated with a relatively low proportion. The proportion of bacteria was reported to be lower in people with conditions such as Crohn's disease or depression compared to a healthy reference group.

What about DNA from Archaea?

Archaea are also microorganisms that live in your gut, but not all people have Archaea. In fact , a recent Korean study found that less than half of the samples tested were positive for archaeal DNA . Furthermore, the relative amount can vary widely, with values ​​between 0.1 and 21.3% .

There are certain conditions that have been shown to generate a high abundance of archaea:

• Irritable bowel syndrome with constipation (IBS-C) .
• A state of chronic inflammation appears to be favored by Methanosphaera stadtmanae. This organism has been shown to triple in relative abundance in people with inflammatory bowel disease (IBD).
• Archaea overgrowth can also occur in the colon and throughout the body. Archaea use hydrogen produced in the gut, which results from carbohydrate fermentation, for methanogenesis. Studies show a strong correlation between excess archaea and constipation.

It is worth noting that archaea could not be reliably detected until recently. Therefore, the published scientific literature is at an early stage. Archaea fulfill several understudied metabolic roles and therefore appear to affect our health in as yet undetermined, indirect ways. There are no known pathogenic archaea, but there is also still much that we do not yet know about them.

What can we expect from fungal DNA?

We previously mentioned fungi , another large group of microorganisms that are also part of your microbiome. Much like the bacteria and archaea that you are already familiar with, fungi interact with human health and disease . Typically, bacteria dominate the microbiome, while only small relative amounts of fungi are present in the gut. We see that our healthy reference group has an average relative amount of fungal DNA below 0.1%.

However, under some conditions , certain fungi can outcompete bacteria, which affects this balance :

• A condition of chronic inflammation such as in people with IBD (Inflammatory Bowel Disease) and more specifically Crohn's disease.
• Autoimmune diseases such as atopic asthma .
• Fungal overgrowth after antibiotic treatment .
  
  

How does your own DNA get into your stool?

Your body is constantly renewing itself. Old cells die as new cells take their place. So, just like your skin, your gut regularly sheds dead material.

This happens so often that about every five days you have a whole new set of cells lining the inside of your gut. When the old cells die, they follow a process that maintains the gut's barrier function , as well as one that includes the destruction of most of their DNA . The fragments that remain can be found in your stool in very small amounts. In most people, less than 1% of the total DNA is found in the stool.

However, there are processes in the intestine that cause a drastic increase in the amount of DNA found in feces. This is because they cause an increase in cells that become damaged or die; or because they interfere with the process of self-destruction. These processes are:

1. Damage
2. Inflammation
3. Infection
4. Abnormal workshop [ 1 , 2 ]
5. Other causes can affect pathological excretion, such as drug abuse.

In addition to being representative of several types of challenges in your gut, having large amounts of DNA in your stool is not desirable as it is an indicator of loss of barrier function and is associated with risk of infection with Clostridium difficile . Furthermore, it reduces the sensitivity of our analyses as it makes it harder for us to detect the lowest levels of microbes.

Conclusion

What sources of DNA we find in your stool and their relative amounts can tell you a lot about your health and well-being. 

• Having a high proportion (>70%) of bacterial DNA is considered normal, while relatively low proportions may indicate challenges.
• Depending on your diet and lifestyle, there may be some archaea DNA. Most people seem to lack archaea. High levels are unusual and may be an indicator of inflammation.
• In general, the proportion of fungal and human DNA should be very low. High levels are associated with several causes and should be investigated further by your GP.

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Author: Christian Lieven