Archaea get food in several fundamentally different ways depending on the species. Some make their own organic molecules from carbon dioxide and inorganic chemicals, functioning as self-sufficient producers. Others consume organic material like sugars and proteins, similar to how animals obtain nutrition. A few even harvest energy from sunlight, though through a completely different mechanism than plants use. This metabolic diversity is one reason archaea thrive in nearly every environment on Earth, from boiling hydrothermal vents to the human gut.
Chemical Energy From Inorganic Sources
Many archaea are chemolithotrophs, meaning they extract energy from simple inorganic chemicals rather than eating organic food. These organisms oxidize substances like hydrogen gas, sulfur, iron, or ammonia the way you might burn fuel, capturing the released energy to power their cells. In volcanic hot springs and deep-sea hydrothermal vents, reduced sulfur compounds (hydrogen sulfide and elemental sulfur) are especially abundant energy sources. Archaea in the order Sulfolobales, for example, specialize in oxidizing iron and sulfur, converting sulfides and elemental sulfur into sulfuric acid at rates far exceeding what would happen through simple chemistry alone.
At hydrothermal vents, hydrogen gas released by water-rock reactions and magma degassing serves as another major fuel. Pyrolobus fumarii, which grows at temperatures up to 113°C, gains all its energy by oxidizing hydrogen. Species of Ignicoccus do the same, reducing elemental sulfur to hydrogen sulfide using hydrogen as their electron donor. These organisms then use that energy to build organic molecules from carbon dioxide, making them fully self-sufficient producers at the base of vent food webs.
On the surface world, archaea in the phylum Thaumarchaeota are among the most important ammonia oxidizers on the planet. They extract energy by converting ammonia into other nitrogen compounds. These organisms account for roughly 20 percent of the tiny microorganisms floating in the world’s oceans, and they are thought to be the most abundant ammonia-oxidizing organisms in soils. Even archaea living on human skin belong to this group, feeding on the ammonia present in sweat.
Methane Production as a Way of Life
Methanogens are a large group of archaea with a unique metabolism found nowhere else in biology: they produce methane gas as a direct byproduct of generating energy. They do this through two main pathways. In the first, they combine hydrogen gas (or a related compound called formate) with carbon dioxide, reducing the CO₂ to methane. This reaction releases a meaningful amount of energy, about 135 kilojoules per molecule of methane produced. In the second pathway, they split acetate (a simple organic acid) into methane and carbon dioxide, though this yields far less energy, only about 36 kilojoules per molecule.
Some methanogens can also use methanol, methylamines, and dimethylsulfide as food sources, stripping off methyl groups and converting them to methane. The substrates methanogens depend on, particularly hydrogen and acetate, are mostly waste products from bacterial fermentation. This creates a natural partnership: bacteria break down complex organic matter and release hydrogen and simple acids, and methanogens consume those byproducts. Without methanogens removing hydrogen, the bacterial fermentation reactions would actually slow down and eventually stall.
This lifestyle has a global impact. Methanogens in rice paddies, wetlands, and other waterlogged soils generate an estimated 10 to 25 percent of global methane emissions. In the ocean, a different group of archaea does the opposite, consuming methane trapped in deep-sea sediments through anaerobic oxidation, acting as a natural brake on this potent greenhouse gas.
Consuming Organic Material
Not all archaea make their own food. Heterotrophic archaea consume organic molecules produced by other organisms, much like fungi or animals do. Species of Ferroplasma and related archaea living in acidic mine drainage environments scavenge proteins and carbohydrates from decaying microbial mats around them. Laboratory experiments have shown these organisms can grow on a range of organic substrates including amino acids, protein fragments, and simple organic acids like acetate and lactate. They possess transport systems for importing sugars and peptides, along with enzymes that break down starch and other complex carbohydrates outside the cell before absorbing the pieces.
Aciduliprofundum boonei, found at deep-sea hydrothermal vents, is another heterotroph. It grows in extremely acidic, hot conditions (60 to 75°C, pH as low as 3.3) and uses elemental sulfur or iron as part of its energy-generating chemistry while consuming organic compounds. In the human gut, Methanosphaera stadtmanae has one of the most restricted diets of any known archaeon: it is completely dependent on acetate as its carbon source, combined with methanol and hydrogen for energy.
Harvesting Sunlight Without Photosynthesis
Some salt-loving archaea (haloarchaea) can supplement their energy supply using sunlight, but they do it in a way that is entirely different from plant photosynthesis. Instead of chlorophyll, they use a purple membrane protein called bacteriorhodopsin. When light hits this protein, it pumps protons (hydrogen ions) across the cell membrane, creating an electrical gradient. The cell then uses that gradient to drive an enzyme that produces ATP, the universal energy currency of life. The protein cycles through several intermediate states as it absorbs light and moves protons, ultimately generating usable chemical energy for the cell’s survival.
This is not true photosynthesis because no carbon dioxide is fixed and no oxygen is produced. It is more of an energy supplement. Haloarchaea typically still consume organic compounds as their primary food source, but in the intensely sunlit, nutrient-poor salt lakes where they live, the ability to top off their energy reserves with light gives them a significant survival advantage.
How Nutrients Actually Enter the Cell
Archaea face a unique challenge in getting nutrients across their cell boundary. Most archaea lack the outer membrane that many bacteria have. Instead, their outermost structure is typically a protein lattice called an S-layer, which acts as the first selective barrier between the cell and its environment. This lattice contains tiny pores, about 1.3 nanometers in diameter, that function as molecular sieves, allowing small molecules through while blocking larger ones.
In ammonia-oxidizing archaea, these nanopores carry electrical charges that actively favor the passage of positively charged ammonium ions while repelling negatively charged molecules. This selectivity means the S-layer is not just a passive filter but an active part of the feeding process, concentrating the cell’s preferred nutrient in the space between the S-layer and the inner membrane. From there, dedicated transporter proteins embedded in the cell membrane pull nutrients inside. Genomic studies have found highly conserved ammonia transporters across different species of ammonia-oxidizing archaea, suggesting this nutrient uptake system is ancient and fundamental to their way of life.
Partnerships With Other Organisms
Many archaea do not feed in isolation. In the guts of cows, termites, and humans, methanogens depend on bacteria to do the initial work of breaking down complex plant fibers like cellulose. The bacteria ferment these tough materials anaerobically, releasing hydrogen, carbon dioxide, and acetate as waste. Methanogens then consume those waste products to fuel their own metabolism. This is a genuine mutualism: by removing hydrogen, methanogens keep the chemical conditions favorable for the bacteria to keep fermenting.
Some Asgard archaea, a group of particular interest because of their close evolutionary relationship to the ancestors of all complex life, live in consortia with bacteria in ocean sediments. These syntrophic partnerships involve the exchange of metabolic products between species, with each partner providing something the other needs. This cooperative feeding strategy may have been central to one of the most important events in the history of life: the origin of eukaryotic cells, which are the building blocks of all plants, animals, and fungi.