Each microbiome is a snowflake. “Invisible Worlds” by MJ Richardson via geograph.org.uk.
We’ve been taught for decades that the microbes inside us outnumber our own cells. And we’ve often been told it’s by a ratio of 10:1. That number was first introduced in 1972 as more of a vague estimate, without much significant factual basis, and has been perpetuated ever since. Well, sort of. In 2014, a researcher from the National Institutes of Health called this very issue into question, and now, Ron Milo and Ron Sender from the Weizmann Institute of Science in Israel, and Shai Fuchs from the Hospital for Sick Children in Canada have offered up a new estimate.
To determine the new ratio, the researchers looked at the available literature about microbe population numbers as they relate to the “reference man.” The reference man is between 20 and 30 years old, weighs about 154 pounds (70 kg) and is about 5’7″ (170 cm). The researchers combed through the original bacteria calculations and found that one of the larger overestimations was for microbes found in the colon.
Known to house one of the largest populations of bacteria, the gut is indeed full of microbes. But, when previous studies made their estimates, they used the density of bacteria per gram of “wet content” of the colon, times the volume of the entire alimentary canal. But, these researchers argue, the bacteria density of the colon is much higher than the rest of the tract, so assuming that the entire alimentary canal is as bacteria-filled as the colon is would be overkill. (If you want to get really philosophical, you could question whether the so-called wet content’s bacteria is even part of our body, since it cycles through us daily.)
The new calculation came down to about 39 trillion bacteria to about 30 trillion human cells, a roughly 1:1.3 ratio. It’s important to note though, that this ratio is still an estimation, not an undisputed fact. As Ed Yong writes in The Atlantic, “my preference would be to avoid mentioning any ratio at all—you don’t need to it convey the importance of the microbiome and scientifically, it’s not all that interesting.”
Human bodies host a staggering number of bacteria, living inside and outside our bodies in the intestines or on the skin. In recent years, these communities of bacteria, called microbiomes, have gotten much more attention, linked to many aspects of health.
The microbiome has also been shown to play a role in cancer. Many bacteria have evolved to change the DNA of other cells as a defense mechanism, which can lead to cancer’s onset or its treatment. Some types of bacteria have been shown to cause cancer under certain conditions. The parts of the body where bacteria are most populous are particularly hardy, effective at protecting the bacteria from penetrating the boundary into more sensitive parts of the body where they could cause harm. But if there’s a breach of normal protections and some of these particular kinds of bacteria get through, they can be carcinogenic.
When good bacteria go bad.
Bacteria can affect cancer in three ways: by changing how much human cells reproduce, by affecting the immune system, and by influencing cell metabolism.
When in a new environment, bacteria can turn off our cells’ immune responses, or turn them on unnecessarily, creating inflammation and autoimmune conditions that break down tissues. Diets heavy in fiber or fat might change how intestinal bacteria metabolize energy, creating an acid as a byproduct that can make colon cancer more likely to happen, though studies so far have come to conflicting conclusions.
The tools are getting better. Tumor cells can be genetically sequenced to see if bacteria have affected them and, if so, the role that bacteria play in the microbiome. Oncologists can engineer bacteria to kickstart the immune system to help combat certain kinds of cancer or other cancer-causing bacteria, or to turn off the genes causing the cells to grow out of control in the first place. Treatments that act as heat-seeking missiles, treating only the cancer and not poisoning the entire body, can work better with boosts from the local microbiome.
Now that they understand some of the basic ways in which bacteria can play a role in cancer, researchers still have a lot of questions. They want to know other ways that bacteria might affect cancer, if they can make different types of treatments more or less effective, if single microbes can make a difference or if they need to be in a particular configuration. They want to know the role of diet in understanding gastrointestinal cancers like colon cancer, or why immunotherapy works better in some microbiomes (like on the skin or in the stomach) than others (like the colon), and why the efficacy of these treatments vary from person to person.
Future research will look at how to use bacteria to diagnose cancer and identify those patients most susceptible to side effects and complications. Though the microbiome requires a lot of interdisciplinary research, says the review, it could hold important answers to fighting and understanding many different types of cancer.
Do you remember cutting paper snowflakes in school? Artist Rogan Brown has elevated that simple seasonal art form and taken it to science class.
These large-scale paper sculptures may evoke snow, but actually trade on the forms of bacteria and other organisms. The patterns may feel familiar, but also a bit alien. You’re not looking at a replica of a microbe, but an interpretation of one. And that distinction, Brown says, is important.
“Both art and science seek to represent truth but in different ways,” the 49-year-old artist, who lives in France, tells Shots. “It’s the difference between understanding a landscape by looking at a detailed relief map and understanding it by looking at a painting by Cezanne or Van Gogh.”
Brown wants to you to feel something looking at these sculptures.
Last year, he met with a group of microbiologists to plan an exhibition on the human microbiome. He became fascinated by the hidden world of microbes and the strange shapes of pathogens. He was particularly interested in humans’ fear of the invisible microbiological world. That meeting led him to spend four months creating Outbreak entirely by hand.
A detailed view of Outbreak shows the delicate forms Brown cut by hand. He says he works with paper because it “embodies the paradoxical qualities that we see in nature: its fragility and durability, its strength and delicacy.”
Those legs, Brown writes on his website, were inspired by the flagella of Salmonella and E. coli, tiny appendages that help the bacteria move.
Brown needed a laser to cut some of the more intricately designed shapes.
Some of Brown’s work is sliced meticulously by hand using a scalpel. Others, like the one above, are also cut using a laser. The end result is a fragile paper sculpture that borrows from what we can see as well as the artistic imagination.
“We live in a world dominated by science,” Brown says. “Art needs to work hard to keep up or use the language and imagery of science for its own ends.”
Giulia Enders is working at the Israelite Hospital (Israelitisches Krankenhaus, IK) author of the bestseller ‘Gut: The Inside Story of Our Body’s Most Underrated Organ’. Enders explains how and why she became fascinated by the functions and the importance of the human gastrointestinal tract, including the gut microbiota, in this talk held in TEDxDanubia, Budapest (Hungary), in May 2017.
TED Talk – How Bacteria Control Our Minds
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This animated documentary celebrates the 17th-century citizen scientist Antonie van Leeuwenhoek, whose discovery of microbes would change our view of the biological world.
