An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form, but it is not a true spore. It is a stripped-down, dormant form to which the bacterium can reduce itself. Endospore formation is usually triggered by a lack of nutrients, and usually occurs in gram-positive bacteria. In endospore formation, the bacterium divides within its cell wall, and one side then engulfs the other. Endospores enable bacteria to lie dormant for extended periods, even centuries. There are many reports of spores remaining viable over 10,000 years, and revival of spores millions of years old has been claimed. There is one report of viable spores of Bacillus marismortui in salt crystals approximately 25 million years old. When the environment becomes more favorable, the endospore can reactivate itself into a vegetative state. Most types of bacteria cannot change to the endospore form. Examples of bacterial species that can form endospores include Bacillus cereus, Bacillus anthracis, Bacillus thuringiensis, Clostridium botulinum, and Clostridium tetani. Endospore formation is not found among Archaea.
Clostridium botulinum is a gram-positive, rod-shaped, anaerobic, spore-forming, motile bacterium with the ability to produce botulinum toxin, which is a neurotoxin.
Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic beta carbon substituent. Tryptophan is also a precursor to the neurotransmitter serotonin, the hormone melatonin, and vitamin B3. It is encoded by the codon UGG.
The human microbiome is the aggregate of all microbiota that reside on or within human tissues and biofluids along with the corresponding anatomical sites in which they reside, including the gastrointestinal tract, skin, mammary glands, seminal fluid, uterus, ovarian follicles, lung, saliva, oral mucosa, conjunctiva, and the biliary tract. Types of human microbiota include bacteria, archaea, fungi, protists, and viruses. Though micro-animals can also live on the human body, they are typically excluded from this definition. In the context of genomics, the term human microbiome is sometimes used to refer to the collective genomes of resident microorganisms; however, the term human metagenome has the same meaning.
Melatonin, an indoleamine, is a natural compound produced by various organisms, including bacteria and eukaryotes. Its discovery in 1958 by Aaron B. Lerner and colleagues stemmed from the isolation of a substance from the pineal gland of cows that could induce skin lightening in common frogs. This compound was later identified as a hormone secreted in the brain during the night, playing a crucial role in regulating the sleep-wake cycle, also known as the circadian rhythm, in vertebrates.
Clostridium is a genus of anaerobic, Gram-positive bacteria. Species of Clostridium inhabit soils and the intestinal tract of animals, including humans. This genus includes several significant human pathogens, including the causative agents of botulism and tetanus. It also formerly included an important cause of diarrhea, Clostridioides difficile, which was reclassified into the Clostridioides genus in 2016.
Tryptamine is an indolamine metabolite of the essential amino acid, tryptophan. The chemical structure is defined by an indole—a fused benzene and pyrrole ring, and a 2-aminoethyl group at the second carbon (third aromatic atom, with the first one being the heterocyclic nitrogen). The structure of tryptamine is a shared feature of certain aminergic neuromodulators including melatonin, serotonin, bufotenin and psychedelic derivatives such as dimethyltryptamine (DMT), psilocybin, psilocin and others. Tryptamine has been shown to activate trace amine-associated receptors expressed in the mammalian brain, and regulates the activity of dopaminergic, serotonergic and glutamatergic systems. In the human gut, symbiotic bacteria convert dietary tryptophan to tryptamine, which activates 5-HT4 receptors and regulates gastrointestinal motility. Multiple tryptamine-derived drugs have been developed to treat migraines, while trace amine-associated receptors are being explored as a potential treatment target for neuropsychiatric disorders.
The hydroxyl radical, •HO, is the neutral form of the hydroxide ion (HO–). Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry. Most notably hydroxyl radicals are produced from the decomposition of hydroperoxides (ROOH) or, in atmospheric chemistry, by the reaction of excited atomic oxygen with water. It is also an important radical formed in radiation chemistry, since it leads to the formation of hydrogen peroxide and oxygen, which can enhance corrosion and SCC in coolant systems subjected to radioactive environments. Hydroxyl radicals are also produced during UV-light dissociation of H2O2 (suggested in 1879) and likely in Fenton chemistry, where trace amounts of reduced transition metals catalyze peroxide-mediated oxidations of organic compounds.
Indole-3-acetic acid is the most common naturally occurring plant hormone of the auxin class. It is the best known of the auxins, and has been the subject of extensive studies by plant physiologists. IAA is a derivative of indole, containing a carboxymethyl substituent. It is a colorless solid that is soluble in polar organic solvents.
Gut microbiota, gut microbiome, or gut flora are the microorganisms, including bacteria, archaea, fungi, and viruses, that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut microbiota. The gut is the main location of the human microbiome. The gut microbiota has broad impacts, including effects on colonization, resistance to pathogens, maintaining the intestinal epithelium, metabolizing dietary and pharmaceutical compounds, controlling immune function, and even behavior through the gut–brain axis.
Clostridium butyricum is a strictly anaerobic endospore-forming Gram-positive butyric acid–producing bacillus subsisting by means of fermentation using an intracellularly accumulated amylopectin-like α-polyglucan (granulose) as a substrate. It is uncommonly reported as a human pathogen and is widely used as a probiotic in Japan, Korea, and China. C. butyricum is a soil inhabitant in various parts of the world, has been cultured from the stool of healthy children and adults, and is common in soured milk and cheeses. The connection with dairy products is shown by the name, the butyr- in butyricum reflects the relevance of butyric acid in the bacteria's metabolism and the connection with Latin butyrum and Greek βούτυρον, with word roots pertaining to butter and cheese.
Indole is an organic compound with the formula C6H4CCNH3. Indoles are derivatives of indole where one or more H's have been replaced by other groups. Indole is classified as an aromatic heterocycle. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indoles are widely distributed in nature, most notably as amino acid tryptophan and neurotransmitter serotonin.
Tryptophol is an aromatic alcohol that induces sleep in humans. It is found in wine as a secondary product of ethanol fermentation. It was first described by Felix Ehrlich in 1912. It is also produced by the trypanosomal parasite in sleeping sickness.
The gut–brain axis is the two-way biochemical signaling that takes place between the gastrointestinal tract and the central nervous system (CNS). The "microbiota–gut–brain axis" includes the role of gut microbiota in the biochemical signaling events that take place between the GI tract and the CNS. Broadly defined, the gut–brain axis includes the central nervous system, neuroendocrine system, neuroimmune systems, the hypothalamic–pituitary–adrenal axis, sympathetic and parasympathetic arms of the autonomic nervous system, the enteric nervous system, vagus nerve, and the gut microbiota.
Urolithins are microflora metabolites of dietary ellagic acid derivatives, such as ellagitannins. They are produced in the gut, and found in the urine in the form of urolithin B glucuronide after absorption of ellagitannins-containing foods, such as pomegranate. During intestinal metabolism by bacteria, ellagitannins and punicalagins are converted to urolithins, which have unknown biological activity in vivo.
6-Hydroxymelatonin (6-OHM) is a naturally occurring, endogenous, major active metabolite of melatonin. Similar to melatonin, 6-OHM is a full agonist of the MT1 and MT2 receptors. It is also an antioxidant and neuroprotective, and is even more potent in this regard relative to melatonin.
3-Indolepropionic acid (IPA), or indole-3-propionic acid, has been studied for its therapeutic therapeutic value in the treatment of Alzheimer's disease. As of 2022 IPA shows potential in the treatment of this disease, though the therapeutic effect of IPA depends on dose and time of therapy initiation.
Indolepropionamide (IPAM) is a chemical compound with the molecular formula C11H12N2O. In vivo (rats), IPAM markedly reduced the proton potential collapse induced by the mitochondrial toxins to nearly baseline levels in both young and old rats and demonstrated free-radical scavenging properties. IPAM was shown to increase complex I and complex IV activity in the mitochondrial electron transport chain, however complex II and complex III were left unchanged. Decreased activity of complexes I and IV results in an inhibition of electron transport that is associated with higher production of ROS. IPAM can also act as a recyclable electron and proton carrier, facilitating reversible endogenous radical and redox reactions, and thereby enabling the formation of a proton gradient that drives mitochondrial ATP synthesis. Thus, IPAM acts as a stabilizer of energy metabolism in mitochondria, thereby reducing the production of reactive oxygen species.
Indoxyl sulfate, also known as 3-indoxylsulfate and 3-indoxylsulfuric acid, is a metabolite of dietary L-tryptophan that acts as a cardiotoxin and uremic toxin. High concentrations of indoxyl sulfate in blood plasma are known to be associated with the development and progression of chronic kidney disease and vascular disease in humans. As a uremic toxin, it stimulates glomerular sclerosis and renal interstitial fibrosis.
Indole-3-carbaldehyde (I3A), also known as indole-3-aldehyde and 3-formylindole, is a metabolite of dietary L-tryptophan which is synthesized by human gastrointestinal bacteria, particularly species of the Lactobacillus genus. I3A is a biologically active metabolite which acts as a receptor agonist at the aryl hydrocarbon receptor in intestinal immune cells, in turn stimulating the production of interleukin-22 which facilitates mucosal reactivity.
