Methanospirillum hungatei is a single-celled microorganism belonging to a group of ancient life forms known as Archaea. It is a methanogen, meaning it has the metabolic ability to produce methane gas. This microbe is recognized by its distinctive long, spiral, or corkscrew-shaped cellular structure. First isolated from a sewage treatment facility, its existence highlights the diversity of microbial life in various environments, including the human body.
What is Methanospirillum hungatei?
Methanospirillum hungatei is classified within the domain Archaea, a group of single-celled organisms with a separate evolutionary history from bacteria. While both are microscopic and lack a nucleus, they differ in their genetic makeup, cell wall composition, and metabolic processes. The cell wall of M. hungatei, for example, lacks peptidoglycan, a substance common in bacterial cell walls, and is instead composed of protein.
The physical structure of M. hungatei is a defining feature. Individual cells are thin, curved rods that join end-to-end to form long, helical filaments. These chains are encased in a durable, sheath-like structure made of a protein called MspA. This sheath holds the cells together, and the entire filament can extend over 100 micrometers in length.
This organism is a strict anaerobe, meaning it cannot survive in environments containing oxygen. To move, the terminal cells at the ends of the filaments use polar tufts of flagella, which are whip-like appendages that enable weak motility.
Natural Habitats and Environments
Methanospirillum hungatei is found in a variety of anaerobic settings, including the sediment of freshwater lakes and ponds. It is also common in the oxygen-poor sludge of sewage treatment plants, where it was first discovered. The organism thrives where organic matter is being decomposed by other microbes, which provides the necessary substrates for its metabolism.
Beyond these external environments, M. hungatei is a known resident of the digestive systems of several animals. It is frequently identified in the rumen of ruminant animals like cattle, where it plays a part in digesting fibrous plant material. In these animals, it contributes to the production of methane, a significant byproduct of their digestion. Its presence is not limited to ruminants, as it has been found in the gut of other mammals.
This methanogen is also a natural inhabitant of the human gastrointestinal tract, specifically the large intestine. The human colon is a densely populated, anaerobic environment, making it a suitable home for this microbe. Here, it coexists with trillions of other microorganisms, collectively known as the gut microbiome.
Metabolic Function and Methane Production
The primary metabolic function of Methanospirillum hungatei is methanogenesis, the biological production of methane. It utilizes simple chemical compounds, primarily hydrogen gas (H₂) and carbon dioxide (CO₂), as its energy sources. In a chemical reaction, it combines hydrogen with carbon dioxide to produce methane (CH₄) and water as byproducts. Some strains can also use a compound called formate as an alternative energy source.
This methanogen does not operate in isolation, instead engaging in a cooperative relationship with other microbes known as syntrophy. In environments like the human gut, other bacteria break down complex organic matter through fermentation, which releases hydrogen gas as a waste product. M. hungatei consumes this excess hydrogen, allowing the fermenting bacteria to continue their function efficiently.
This syntrophic relationship is a form of microbial teamwork. Bacteria such as Smithella and Syntrophomonas break down organic compounds that they cannot fully process alone under anaerobic conditions. The hydrogen they produce is quickly used by M. hungatei, which maintains low hydrogen levels that make the initial breakdown thermodynamically favorable.
The machinery for methanogenesis involves a series of specialized enzymes and cofactors unique to methanogens. The complete genome sequence of M. hungatei has revealed the genes that code for these complex pathways. These genetic blueprints control the step-by-step conversion of hydrogen and carbon dioxide into methane.
Association with Human Health and Disease
The presence and activity of Methanospirillum hungatei in the human gut are linked to certain physiological effects and gastrointestinal conditions. Its methane production is not a benign process; the gas itself acts as a neuromuscular signaling agent in the intestines. Methane can slow down intestinal transit time, which is the speed at which food and waste move through the digestive tract. This slowing effect can contribute to and worsen constipation.
An overgrowth of methanogens like M. hungatei can lead to a condition known as Intestinal Methanogen Overgrowth (IMO). IMO is distinct from Small Intestinal Bacterial Overgrowth (SIBO) and is specifically characterized by an excessive amount of methane-producing archaea in the gut. This condition is strongly associated with constipation-predominant Irritable Bowel Syndrome (IBS-C).
The symptoms linked to high levels of methane in the gut extend beyond just constipation. Severe and persistent bloating is a frequent complaint, as the trapped methane gas expands the intestines, causing a feeling of fullness and visible abdominal distension. This can be accompanied by excessive flatulence and abdominal discomfort or pain.
Diagnosing the overgrowth of methanogens is done through a non-invasive procedure called a hydrogen and methane breath test. After consuming a sugar solution, a patient breathes into a collection device at regular intervals. The device measures the concentration of hydrogen and methane gases in the breath. An elevated level of methane gas is a direct indicator of the activity of methanogens like M. hungatei in the gastrointestinal tract, confirming a diagnosis of IMO.