Nature is a large factory of highly complex biochemical compounds, some of which have the purpose of defense by synthesizing poisons that can also be lethal to humans.
Many toxins that affect humans are substances produced by living things. Some animals, plants, protists or bacteria are authentic living chemical laboratories that produce the most varied toxins.
In living beings we can find powerful poisons, such as tetradotoxin present in fugu fish, conanthoquin-p present in cone worms, muscarine in the fungus Amarita muscaria or cyanide derivatives in a good number of seeds. Or even more toxic substances. And they are closer than you might think.
A tree well known for its high toxicity grows in the rainforests of Southeast Asia and Northern Australia. Commonly known as nux vomica, the seeds of Strichnos nux-vomica are carriers of two powerful toxins: brucine and strychnine.
Strychnine is considered the fifth most potent biological poison in the world. It is a neurotoxic alkaloid that attacks the central nervous system. It causes a general contraction of the body’s muscles and causes convulsions that can last up to 2 or 3 hours, the time it takes for the victim to die. 25 µg of strychnine is estimated to be the lethal dose for a mouse, and for adult humans it is estimated to be between 50 and 100 mg.
It is a toxin that is rapidly absorbed by the mucous membranes and the gastrointestinal tract, but does not occur through the skin. Once it enters the body, the toxin is rapidly distributed through the tissues and is metabolized in a very short time. Its elimination in the urine is very low (no more than 20%).
One of the most powerful poisons in the world is not found in animals or plants, but in small, single-celled aquatic organisms. In traditional classifications they are grouped as algae, although they are evolutionarily closer to other organisms traditionally considered protozoa, such as the genus plasmodium (the parasite that causes malaria) than with true algae. We’re talking about dinoflagellates.
Dinoflagellates are peculiar organisms; many are photosynthetic but also consume prey by phagocytosis; organisms capable of performing both actions are called mixotrophs. Many have a cellulose covering, called teak, that covers the cell body and protects it, and all have two flagella, one that wraps around the body like a belt, and another long one that it uses to propel itself along.
When an unusually high number of dinoflagellates concentrate in a body of water, it turns a reddish color. This phenomenon, which resembles a biblical curse, is called “red tide”, and can cause intoxication, both by drinking the water and consuming animals that live there, especially if they are filter feeders, such as mussels or clams, as they retain the dinoflagellates in your body.
The fourth most potent biological toxin is produced by a dinoflagellate: Gambierdiscus toxicus. Maitotoxin is a molecule composed of 32 carbon rings and is one of the largest and most complex non-protein and non-polysaccharide biomolecules. It is a powerful toxin that causes heart failure and death in a very short time, both by ingestion, inhalation and even contact. It is estimated that 2.5 ng of maitotoxin is enough to kill a mouse. The lethal dose in humans has not been estimated.
Batrachotoxin is the most potent animal poison known. It is a neurotoxic alkaloid that induces irreversible depolarization of nerves and muscles, which can lead to paralysis, fibrillation and heart failure. It is excreted through the skin of frogs of the genus philobates, native to Colombia, and also by some birds from New Guinea. It is so potent that just 10 ng of toxin can be lethal to a mouse and between 100 and 200 µg to a human.
A curious fact is that frogs raised in captivity do not produce batrachotoxin, so it is suspected that the toxin is not produced by their metabolism, but that they probably obtain it through their diet. Beetles of the genus chorusin, which produce toxins of the same group, although in much lower concentration. If this hypothesis is true, frogs and birds would sequester the toxin, metabolize it into batrachotoxin, to which they are immune, and concentrate it, excreting it through their skin.
When one living being is attacked by another, it usually follows a response called hyperarousal. It is described as a fight or flight reaction, that is, the organism that perceives the attack tries to fight back or avoid the attack.
Plants cannot flee, in the literal sense of the term, nor can they respond with an active attack, so they often opt for preemptive defense. Some plants generate structures that repel the ‘attacker’: they have thorns or spurs as a way to avoid the attack. It would be their form of “escape”. But others opt for biochemical defense. And is that plants have an extraordinarily complex secondary metabolism and are able to synthesize a wide range of chemical substances with which to “fight” against their aggressor.
Of them all, the one with the deadliest defense is the beaver (Ricinus communis). This plant came to synthesize the most lethal plant toxin, ricin, the most poisonous substance produced by a eukaryote, and the second of all living beings. Unlike strychnine, batrachotoxin or maitotoxin, which are relatively two alkaloids and a chain of carbon rings, ricin is a protein. Its toxicity occurs at the cellular level, inhibiting protein synthesis. Symptoms are different depending on the route of exposure, but in any case, a minimal dose can be lethal.
1. Botulinum toxin
The most lethal toxin produced by a living being is botulinum, produced by the bacterium Clostridium botulinum. It is an anaerobic bacterium, it only grows in the absence of oxygen, but it is practically ubiquitous. It can grow on food, especially canned food, as long as it does not come into contact with air. During the fermentation process, bacteria produce gas, so if a canning container is contaminated, it will look bloated.
Botulinum toxin is a neurotoxin of a protein nature, just a few nanograms are enough to kill an adult. It causes muscle and nerve paralysis by preventing the release of the neurotransmitter acetylcholine; an intoxication that has its own name: botulism.
A small amount of the toxin is found in ‘botox’, which paralyzes muscles to minimize wrinkles. With carefully measured doses, it is also used as a muscle antispasmodic.
Now that you know these substances, it’s best to stay away from them, even though many have medical or cosmetic applications in the right doses.
Dumbacher, JP et al. 2004. Melyrid Beetles (Choresine): A putative source for the batrachotoxin alkaloids found in poisonous frogs and toxic passerine birds. Proceedings of the National Academy of Sciences, 101(45), 15857-15860. DOI: 10.1073/pnas.0407197101
EASA 2008. Ricin (from Ricinus communis) as undesirable substances in animal feed – Scientific Opinion of the Panel on Contaminants in the Food Chain. EFSA Journal, EFSA Journal. DOI: 10.2903/j.efsa.2008.726
Montecucco, C. et al. 2005. Botulinum Neurotoxins: Rebirth of an Ancient Killer. Current Opinion in Pharmacology, 5(3), 274-279. DOI: 10.1016/j.coph.2004.12.006
Stoecker, DK 1999. Mixotrophy among Dinoflagellates. Journal of Eukaryotic Microbiology, 46(4), 397-401. DOI: 10.1111/j.1550-7408.1999.tb04619.x
National Biotechnology Information Center (2022). PubChem Compound Summary for ICD 441071, Strychnine; CID 71460273, Maitotoxin; and CID 6324647, Batrachotoxin.