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Every human body contains a complex ecosystem of trillions of microorganisms that are vital to your health throughout your life. These microbial symbionts help you digest food, synthesize essential vitamins, protect against infection, and perform many other critical functions. In turn, the microbes, mostly concentrated in your gut, live in a relatively stable, warm environment with a constant food source.
But what happens to these symbiotic partners after you die?
As an environmental microbiologist who studies the necrobiome—the microbes living in, on, and around a decomposing body—I was interested in our postmortem microbial legacy. One might assume that your microbes die with you—once your body starts to decompose and your microbes are released into the environment, they can’t survive in the real world.
In a newly published study, my research team and I present evidence that microbes not only continue to exist after you die, but also play a significant role in decomposing your body, allowing new life to develop.
Microbial life after death
When you die, your heart stops pumping the blood that delivers oxygen throughout your body. Deprived of oxygen, cells begin to destroy themselves in a process called autolysis. Enzymes in these cells — which normally digest carbohydrates, proteins, and fats for energy or growth in a controlled manner — begin to break down membranes, proteins, DNA, and other cellular components.
The products of this cellular breakdown become excellent food for your symbiotic bacteria, and without your immune system to keep them in check and a constant supply of food from your digestive tract, they begin to exploit this new food source.
Gut bacteria, especially a class of microbes known as Clostridia, spread throughout your organs and decompose you from the inside out in a process called putrefaction. Without oxygen inside your body, your anaerobic bacteria rely on oxygen-free energy processes, such as fermentation. They produce the characteristic odors of putrefaction.
From an evolutionary perspective, it makes sense that your microbes would have developed ways to adapt to a dying host. Like rats on a sinking ship, your bacteria will soon have to abandon their host and survive in the environment long enough to find a new host to colonize. Using your body’s carbon and nutrients, they can increase their numbers. A larger population means a higher probability that at least a few of them will survive the harsher conditions and successfully find a new host.
Microbial invasion
If you are buried in the ground, your microbes are released into the soil via decomposition fluids as your body decomposes. They are exposed to a completely new environment and encounter a completely new microbial community in the soil.
Mixing or merging of two different microbial communities often occurs in nature. Merging occurs when the roots of two plants join, when sewage flows into a river, or even when two people kiss.
The outcome of the mixing—which community becomes dominant and which microbes are active—depends on a variety of factors, such as how much the microbes alter the environment and what was there first. Your microbes are adapted to the stable, warm environment inside your body, where they have a steady supply of food. By contrast, soil is a particularly harsh place to live, a highly variable environment with sharp chemical and physical gradients and wide fluctuations in temperature, moisture, and nutrients. What’s more, soil already contains an unusually diverse microbial community, full of decomposers that are well adapted to the environment and would presumably outcompete any newcomers.
It’s easy to imagine that your microbes will die as soon as they leave your body. However, previous studies by my research group have shown that the DNA signatures of microbes associated
Sourse: www.livescience.com
