Biology for Writers: The Human Microbiome

Good morning, everyone! Happy Monday! It’s the second week of November (already!), so here I am with a quick post on a bioscience topic which may be of interest to some of the writers who read my blog (and don’t have that much background in science). Let’s get right to it!

The Overview

One of the biggest topics in science right now is the human microbiome. What is a microbiome, you ask? Well, it’s simply the entire set of microbes that inhabit the human body.

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Yes, that’s right–there are microbes in you, right now, and they’re even supposed to be there! As a matter of fact, there are more bacteria, archaea (basically extreme-environment microbes), and unicellular fungi in your body than there are human cells. Yes, you heard that right–we humans are more microbial than human. Blows your mind a little, doesn’t it?

So what do these microbes do for us? Are they good for anything, or do they just sit there? Well, my friends, I’m glad you asked. Let’s take a look at some of the parts of our bodies where our normal microbes are most influential.

The Mouth

We all know about dental plaque, and brushing our teeth so we don’t get it. (Seriously, I hope you all brush your teeth, ’cause plaque is disgusting.) But your mouth also contains 50-100 billion normal bacteria of at least 500 different species, mostly anaerobes, or bacteria that don’t require oxygen to live. (In fact, some anaerobes die when exposed to oxygen.) Streptococcus mutans and S. sanguinis, the organisms that cause plaque when they build up into a biofilm, are both “facultative anaerobes,” which means that they can either use oxygen or not depending on conditions in their environment (the mouth). Many other normal mouth bacteria can cause problems for the human host if there is bleeding in the mouth, or some other abnormal condition, bringing up an important point for the microbiome in general: Microbes that are normal inhabitants of our bodies (“normal flora” or “microbiota”) can be pathogenic if they are moved to a different spot or if something abnormal happens. These are called “opportunistic pathogens,” and we’ll see more of them as we move through the body.

The Gastrointestinal Tract

This is one of the places where the human microbiome is most important and best characterized; a lot of work has been done linking the gut microbiome composition to everything from diet to Parkinson’s disease. And gut microbes do a lot for us. For instance, we can’t digest vegetables without our gut microbes, and other microbes make vitamin K for us. That’s pretty darn helpful of them, don’t you think?

But when I say “gut microbiome,” what am I talking about? It turns out that not every part of the human body is colonized by microbes; accessory organs such as the liver and pancreas are sterile, and the stomach has a very low level of microbes due to the high acid content there (the stomach’s pH, a measure of its acidic content, is about 2–so very acidic). Not many things can survive the acidic environment of the stomach, which is why it’s great for digestion. One Helicobacter species, however, survives by burrowing into the stomach lining and secreting basic compounds, which neutralize the surrounding acid to create a neutral pH (good for life). This species can also cause stomach ulcers when it has lived in the stomach lining for a long time.

So if the stomach doesn’t have very many microbes, where is this gut microbiome I’ve been telling you about? Most of the gut microbiota live in the ileum (the last part of the small intestine) and in the colon (also known as the large intestine), where, as I mentioned, they help us digest our food, give us nutrients, and take up space so invaders can’t enter. This is known as a “mutualism,” in which both symbiotic partners benefit from their relationship. How do the bacteria benefit from us? Well, most parts of the body are at a neutral pH, which as I’ve already said is good for life, and they remain at a constant warm temperature, which allows microbes to grow.

I also just want to point out quickly that taking too many antibiotics can interrupt your gut microbes, and thus actually make you susceptible to sickness, since with space freed up by antibiotic treatment, pathogens can easily colonize your gut. Since this post is mainly about the microbiome, that’s all the space I can give to this extensive topic, but if you’re interested in learning more, feel free to comment below!

The Skin

The skin is one of our first defenses against microbes, since we are constantly sloughing off dead skin cells, but it is also colonized by many microbes. Similar to the gut microbiome, these take up space on your skin, preventing infection by pathogens. The skin microbiome also includes Staphylococcus aureus, an opportunistic pathogen which normally lives on the skin surface, but can cause problems when it penetrates deeper into the body. For instance, if you have a deep puncture wound, your normal S. aureus may get under your skin (literally) and cause nasty carbuncles and things when it infects you. So if you’re writing a novel and your character gets wounded, this is one thing that could follow that up if you want to give them extra torture be realistic about the consequences of wounding.

Find out More!

Here are some resources if you’d like to find out more about the human microbiome!

Human Microbiome Project–This would be a great resource if you want to find out some of the specific microbes that exist in each place on the human body (there are many, many more microbes than the ones I talked about today).

The Gut Microbiome in Health and Disease–A scientific paper about the gut microbiome. (Please note this is intended for a scientific audience, so it may be a bit dense.)

When Gut Bacteria Change Brain Function–An interesting general-audience article about how gut bacteria impact the brain.

I will continue to add more resources here as I find them! If you find interesting resources, feel free to let me know in the comments and I will consider adding them to this page.

That’s it for my first Biology for Writers post! Are you thinking of using the microbiome in your story? If so, how? Is there anything else you’d like to know about the microbiome? (I’m definitely not an expert, but I can point you to more resources if you’d like!) Are there other biology topics you’d like to see addressed in this monthly post series? Let me know in the comments!


Your Questions Answered, Part 1: Biomedical

Hey, everyone! A couple weeks ago, I put out a call for questions from writers about sci-fi genetics things. Genetics and biotechnology are becoming really popular in science fiction, going right along with the scientific revolution they’re currently undergoing, and as a genetics major, I really like to see these topics accurately portrayed in fiction. Thank you so much to Victoria Howell and H. Halverstadt for asking these questions!

Is it possible in the future that a compound could be invented to speed up healing of all tissues?

The short answer is: anything’s possible, right? Actually, tissue regeneration, which is kind of similar to this question, is becoming a big thing; I knew someone once who was applying to a tissue regeneration master’s program at Brown University. As this article explains, though, speed healing is a tradeoff for accuracy in rebuilding tissues (the article also has some other great thoughts about regeneration, more than I can tell you, if anyone’s interested).

How do you think people in the future would respond physiologically to bacterial and viral infections?

I would say essentially the same way they do today, and presumably the same way they’ve been responding for thousands of years. Evolution (or adaptation, if you prefer) is a really slow process. It’s very difficult to imagine that, even in a thousand years, humans will have evolved something radically different from the current immune system; think of the expression, “If it ain’t broke, don’t fix it.” (But if a really aggressive disease swept through and wiped out everyone who couldn’t cope with it . . . who knows?)

In a society where human genetic engineering is commonplace, how do you think sickness would be affected? What kind of diseases can’t be eradicated by genetic engineering or vaccines?

This is a difficult question. In theory, humans could master the incredibly complex immune system and ramp it up somehow by genetic engineering, but that’s a far-off possibility. I don’t think genetic engineering would impact infectious diseases so much as terminal illnesses, and certainly genetic diseases. (Sure, if someone had a genetic predisposition to an infectious disease, someone could use gene therapy to reduce their risk of that disease, but I’ve actually never heard of a case like that.)

As far as eradication, some kinds of diseases are easier to eradicate than others. Smallpox was a good candidate for eradication for a couple reasons: 1) it has no animal vector (i.e. doesn’t spend part of its life cycle in an animal or an insect somewhere, which makes diseases very difficult to control—think malaria), and 2) when you’ve had smallpox once, you don’t get it again. Anything that doesn’t fit these criteria (which is a lot of diseases!) is difficult to eradicate, although the gene drive is being tested against malaria and other mosquito-vector diseases (see this post). Any kind of parasite (think tapeworm) could probably be eradicated with good living conditions (you don’t hear about Americans getting parasitic worms, do you? But they’re all over third-world countries). So bottom line, it’s hard to say, but it really depends on the kind of disease, what resources are available, and how much time is available to develop those resources.

What are the possibilities of a pandemic happening?

So a “pandemic” is defined as a disease outbreak that becomes prevalent over an entire country or internationally. This actually has happened and will probably happen again; H1N1 (swine flu), Ebola, HIV, and (I believe) Zika all count as pandemics. What I think this question is actually getting at is the probability of a world-decimating pandemic, and that’s hard for me to say with my limited medical knowledge. My guess is that it could happen, and if it did, it would devastate third-world countries with few public health efforts first, and unless it was an extraordinarily fast-spreading pathogen, advanced countries like the US would have plenty of time to prepare vaccines and minimize cases.

Cyber limbs are becoming more common every day. What limitations might someone with cyber technology face?

This is really more a computer science thing, as far as I can tell, but I’ll do my best to give thoughts from the biology side—just take everything I say here with a grain of salt. J So my guess is that cyber limbs would require some kind of wiring into the brain, for starters, and that would require some really tough, non-rustable wires (they would have to be metal coated in nontoxic plastic or something). Also, the body often rejects foreign objects, like nonsimilar organ transplants, as being “nonself,” causing the immune system to go on full attack mode and eventually making the person very sick. I expect this would happen with cyber technology as well. (I’ve actually heard of research projects dealing with the difficulty of creating bioadhesives compatible with the body, for transplants and what have you.) So my guess is most of the problems would be during the implantation phase.

Do you see new disease mutations happening to replace any that are eradicated? What kind of diseases do you think they would be, and how do you think people in this future world would physiologically respond to them?

To the first part of the question, I say absolutely. Disease organisms, like all organisms, mutate all the time. To give some background information, the average error rate per DNA replication cycle (which is all the mutation rate is, really) is one error per 106-108 nucleotide base pairs. That’s one error per 1 million-100 million bases, which is pretty low, really, but when you consider how large the genome is, and how many copies of the genome are present in multicellular organisms, it’s staggering. Taking the 100 million number for the human body, 37.2 trillion cells in the body, and a genome of about 3 billion bases, that comes out to about 1.1 quadrillion mutations in the human body every cell cycle, which is staggering! The moral of the story is, mutations happen in every organism, all the time, so yes, new disease mutations could certainly happen, whether in bacteria, viruses, or fungi.

With regards to human disease response physiology, humans aren’t exactly my specialty, but I expect it would be much the same as today. Evolution is a really slow process, unless humans sped it up by somehow engineering themselves with better immune systems, which is theoretically possible, but I’ve heard the immune system is so complex that I doubt this would be feasible without a technological breakthrough similar to that of next-generation sequencing (which revolutionized genetics and actually created the whole new field of genomics).

How do you think aging would be affected by genetic engineering and advanced medicine?

This is an intriguing and highly relevant question. Aging is one of the great scientific mysteries of our time, and as you can imagine, there are many scientists out there who are devoted to conquering it. To give some background, there are several current hypotheses about how aging happens. First, and perhaps most prevalently, the telomere theory: telomeres are the ends of our chromosomes, which shorten with each successive DNA replication. There is an enzyme called telomerase which re-lengthens them, but eventually, as we age, our telomeres shorten further and further, and the theory is that this contributes to the decline of our cells as we age. (This hypothesis is supported by the fact that cancer cells’ and germ-line cells’ telomeres don’t shrink at all.) Another hypothesis is called “antagonistic pleiotropy,” the idea of mutations accumulating in body cells (see above question), eventually reaching a detrimental level. Of course, one’s environment also plays into aging; people who eat healthy and so forth “age better” than those who don’t.

With that very long background discussion, we can get to some of my educated guesses. Perhaps humans would be able to engineer some kind of hyperactive telomerase to prevent the degradation of telomeres, or an extra-corrective DNA polymerase that could go back and fix its mistakes at a higher rate than normal DNA pol. And it might eventually be considered a form of gene therapy to go back and “fix” a person’s aged genes and try to make them younger again (although it’s a long shot that this would work, in my opinion). Environmental factors, of course, can always be improved; good diets, for example, might become more prevalent in the future.


That’s it for me today!

What do you think? Does this apply to any of your writing? Have you thought about these questions before? Do you have any follow-up questions? (I might not be able to answer them all, but I’ll give it my best shot!) Tell me in the comments!

Are Allergies Genetic? (Said the Science Nerd)

Yes, yes, on second Saturdays of the month, everything I say is from science-nerd mode, isn’t it? Specifically biology-nerd mode. I suppose that’s what happens when one is a genetics student.

Really, though, a couple of things influenced me to ask myself this question. Number one, I am a genetics student; therefore, I am curious about genetics. Number two, I have allergies, as does everyone else in my family. We’ve been sneezing off the hook for about three months now. I am mostly allergic to pollen (a real letdown for a plant lover), but people in my family are allergic to all sorts of things: horses, corn, sheep, hazelnuts, cats, you name it. So I wondered: are allergies genetic?

I asked Google that question, and it was kind enough to direct me to this interesting article, which not only answered my original question, but added more to the answer. It turns out that allergies are genetic, passed from parent to child. They are also sex-related; for example, girls are more predisposed to have allergies if their mothers also have allergies, and vice versa for boys.

Another article points out that there are different kinds of “allergic diseases,” including eczema and asthma as well as hay fever (pollen allergy). And, like anything else, allergies are influenced by environmental factors, including air pollution, chemicals, and types of animals and plants in the area, as well as by genetics. (See this abstract for more.)

Well, this turned out to be a short post. There are some quick facts about allergy genetics for you!

What do you think? Do you have allergies or something similar, like asthma? If so, do your family members have it, too, and have you ever wondered whether it was genetic? Tell me in the comments!