Microorganisms often cause illness, but the microbial world is diverse. Archaea, a distinct domain of life, are microscopic entities often mistaken for bacteria. This raises a common question: Do archaea cause disease in humans? While some microbes are pathogens, archaea’s role in human health, particularly concerning disease, is complex.
Understanding Archaea
Archaea represent one of the three fundamental domains of life, alongside bacteria and eukaryotes. Though single-celled organisms resembling bacteria under a microscope, archaea possess unique biological characteristics. Their cell walls lack peptidoglycan, found in most bacteria, instead using pseudopeptidoglycan, glycoproteins, or protein-based structures.
Archaea’s cell membrane lipids are ether-linked phytanyl units, unlike the ester-linked fatty acids in bacterial and eukaryotic membranes. Some archaeal membranes can even form a single lipid monolayer rather than a bilayer. While prokaryotes like bacteria, archaea share molecular mechanisms, such as transcription and translation, more akin to eukaryotes. They exhibit remarkable metabolic diversity, utilizing various energy sources from organic compounds to ammonia, metal ions, or hydrogen gas. Historically recognized for thriving in extreme environments like hot springs and salt lakes, archaea are now known to be abundant in more common habitats, including soil, oceans, and marshlands.
Archaea in the Human Body
Archaea are a common part of the human microbiome, inhabiting various locations within the body. They are found in the gut, mouth, and on the skin. Unlike many bacteria, archaea are commensal or neutral inhabitants, coexisting with humans without causing harm.
A prominent example of archaea in the human body are methanogens, which produce methane. Methanobrevibacter smithii is a prevalent methanogen found in the human gut, where it plays a role in facilitating digestion. These organisms contribute to the microbial environment by consuming hydrogen produced by other gut microbes and converting it into methane. This process can help maintain a balanced gut environment, potentially protecting against certain intestinal disorders.
Exploring Disease Associations
Despite their widespread presence, archaea are not widely recognized as primary human pathogens. No known archaea have been definitively identified as direct causes of human disease. Direct causation of disease by archaea is rare or unproven.
However, archaea have been associated with certain health conditions, though these are correlations, not direct causation. For example, Methanobrevibacter oralis is detected more frequently in patients with periodontitis than in healthy individuals. Similarly, Methanobrevibacter smithii has been linked to diverticulosis and, in mouse models, to increased obesity when interacting with other bacteria. In such cases, archaea’s role is secondary, acting synergistically with other microbes or indicating an altered microbial environment, rather than being the sole cause of illness. Research continues to explore these associations, but archaea are not considered disease-causing agents in the traditional sense.