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Ranked: Biotoxins in Nature, by Lethal Dose

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Biotoxins: Poisons of the Natural World

Biotoxins are harmful substances that come from living organisms.

They can take many forms, from the venom of a snake or spider to the neurotoxins produced by certain types of algae or microbes.

In the infographic above, we look at some common biotoxins in the natural world and rank them based on how deadly they are to an average 70 kg (154 lb) human being.

Ranking Biotoxins on a Toxic Scale

A basic concept in toxicology is that “only the dose makes the poison”. Everyday harmless substances like water have the potential to be lethal when consumed in large enough concentrations. Measuring a lethal dosage is very difficult.

First, living things are complex: factors like size, diet, biochemistry, and genetics vary across species. This makes it difficult to qualify toxicity in a universal way.

Second, individual factors like age or sex can also affect how deadly a substance is. This is why children have different doses for medications than adults.

Third, how a poison is taken into the body (orally, intravenously, dermally, etc.) can also impact its deadliness.

As a result, there are many ways to measure and rank toxicity, depending on what substance or organism is under investigation. Median lethal dose (LD50) is one common way for measuring toxicity. LD50 is the dose of a substance that kills 50% of a test population of animals. It is commonly reported as mass of substance per unit of body weight (mg/kg or g/kg). In the graphic above, we curate LD50 data of some select biotoxins found in nature and present them on a scale of logarithmic LD50 values.

What’s surprising is just how potent some toxins can be.

Bits and Bites about Biotoxins

While one would think that biotoxins are avoided at all costs by humans, the reality is more complicated. Here are some interesting facts about biotoxins present in nature, and our unusual relationships with the organisms that create them:

1. Fungi and molds make poisons called mycotoxins
Mycotoxins are a global problem. They affect crops from many countries, and can cause significant economic losses for farmers and food producers.

2. Phytotoxins can defend plants…and attack cancer
Plants use phytotoxins to defend themselves other organisms, like humans. Urushiol, for example, is the main toxic component in the leaves of poison ivy, poison oak, and sumac. But the Pacific yew tree produces taxol that’s valuable in chemotherapy treatments.

3. Fire salamander toxin is an ingredient in Slovenian whisky
Though not widely available, some whisky makers in Slovenia use samandarine from the fire salamander to create a psychedelic alcohol.

4. Ciguatoxins exist in the guts of reef fish
Very unique species of bacteria living in the digestive tract of reef fishes make ciguatoxin. They transmit this poison to other organisms when the host fish is eaten.

5. Pufferfish are deadly, but also delicious
Pufferfish contain tetrodotoxin, a potent neurotoxin in their ovaries, liver, and skin called tetrodotoxin. Despite being a delicacy in many countries around the world, it has a lot of strict regulations because of its ability to kill people. In Japan, for example, only specially licensed chefs can prepare pufferfish for consumption.

6. Batrachotoxin is lethal to the touch
The skin of some poison dart frogs secretes a deadly substance called batrachotoxin. It is so potent that simply touching the poison can be fatal. Indigenous people of Central and South America used batrachotoxin to poison the tips of hunting weapons for centuries.

7. Botox contains the most deadly biotoxin known
Commercial botox uses an extremely small amount of biotoxin from a microbe called Clostridium botulinum. It paralyzes the muscles, preventing contraction (i.e. wrinkling). It is the deadliest known biotoxin on Earth. One gram of botulinum toxin can kill up to one million people.

Caveats of Measuring and Reporting Biotoxicity

While we use LD50 data to rank biotoxicity, it isn’t an exact science. There is room for improvement.

For starters, no LD50 data exists for humans. That means data from other organisms has to be converted to apply to humans. There is a lot of contention amongst scientific communities about how accurate this is.

There has also been an increasing effort to move to new methods of measuring toxicity that are not harmful to animals. Several countries, including the UK, have taken steps to ban the oral LD50, and the Organisation for Economic Co-operation and Development (OECD) abolished the requirement for the oral test in 2001.

Now, new ways of evaluating toxicity are under investigation, like cell-based screening methods.

Correction: Water was mislabeled on a previous version of the infographic. Full sources here

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Healthcare

Visualized: What Lives in Your Gut Microbiome?

The human gut microbiome contains a world of microbes. We look at the the bacteria that deeply affect our health and well-being.

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Visualized: What Lives in Your Gut Microbiome

Inside all of us lies a complex ecosystem of microbes. It includes bacteria, fungi, and even viruses that live in virtually every part of our bodies.

Researchers are continuing to discover how deeply connected our overall gastrointestinal health—gut health—is to these microbes.

Because bacteria outnumber all other microbes, we take a look at which ones live inside of us and what they do.

The Bacteria of the Gut Microbiome

The gut microbiome is composed of six main types of microbes. Each of these types of microbes has a unique function and role within the human body:

  • Firmicutes: Firmicutes break down complex carbohydrates and produce short-chain fatty acids for energy. They help maintain the functioning of the gut barrier, which obstructs bacteria, harmful microorganisms, and toxins from entering the bloodstream through the intestinal tracks. Firmicutes are also linked to obesity and metabolic disorders when imbalanced.
  • Actinomycetota: Actinomycetota break down complex carbs and produce vitamins B12 and K2, which are crucial for calcium absorption and energy generation in the body. They also protect the gut from harmful pathogens.
  • Pseudomonadota: Pseudomonadota lowers the gut’s redox potential, a measure of the balance between oxidants and antioxidants in the gastrointestinal tract. This is important for breaking down, storing, and using energy. They do this by producing short-chain fatty acids and breaking down complex molecules, promoting the growth of other beneficial gut microbes.
  • Fusobacteriota: Fusobacteriota can activate inflammatory responses to fight pathogens. But when imbalanced, they can contribute to inflammation and disease, such as periodontal disease.
  • Bacteroides: Bacteroides break down complex carbohydrates, regulate the immune system, and produce vitamins and metabolites important for overall health in the human gut microbiome.
  • Other: The “other” category includes a diverse range of microbes that contribute to various functions within the gut. These include various types of bacteria including TM7 (oral bacteria), cyanobacteria, acidobacteria, and verrucomicrobiota.

Dynamic Composition of the Microbiome

Interestingly, the proportions of these six microbe populations vary throughout the gastrointestinal tract.

Section of Gut MicrobiomeExponential Microbial Population (CFU/ml)Dominant Microbe
Mouth10⁵Firmicutes
Esophagus10⁷Firmicutes
Stomach10³Actinomycetota
Duodenum (Small Intestine)10³Firmicutes
Jejunum (Small Intestine)10⁵Firmicutes
Ileum (Small Intestine)10⁸Firmicutes
Large Intestine10¹⁰-10¹²Bacteroides

The presence, absence, and dominance of each of these microbes is based on their functionality. For example, in the mouth and esophagus, the microbial populations are relatively low. But the dominant microbe found here, Firmicutes, helps begin the process of breaking down sugars and carbohydrates from ingested food.

Meanwhile, the stomach is a harsh environment, with low pH levels that limit microbial growth. A small population of microbes is still present here.

The microbial population becomes more diverse in the small intestine. Here, Firmicutes and Actinomycetota are the dominant species, but Bacteroides and other microbes begin to make up a more substantial portion of the population.

The microbial population further diversifies in the large intestine, with Bacteroides and other microbes making up the majority of the population.

These proportions of bacteria in the gut microbiome represent the typical ratios for the average human body. But they can be influenced by factors including medical history, diet, age, and even geographical location.

The Gut-Brain Axis

The six microbe populations have effects way outside the gastrointestinal tract too.

The Gut-Brain Axis is a two-way link between the gut and the brain. This connection involves physical pathways and various forms of communication, including hormones, metabolism, and immunity.

Through these connections, the gut sends the brain signals when troubled. A distressed stomach or intestine is linked to anxiety, stress, depression, and other mental health issues. Irritable bowel syndrome (IBS) is another example of a disease influenced by the gut microbiome.

At the same time, the brain also signals the gut when distressed. Scientists believe that emotions like anger, anxiety, sadness, and happiness trigger gut issues.

Towards a Healthy Gut

The gut is known as our body’s “second brain” and more and more people are now paying close attention to their gut health.

Over the last two decades, we’ve gained a better understanding of how the microbiome affects human health. One example of this is the gut-brain axis. Changes in the microbiome have also been connected to various diseases.

Understanding this microbiome has opened up new opportunities in medicine and healthcare, as the knowledge of the role of every microbe could also uncover new treatments for illnesses linked to it.

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