Microbiology Terms Starting With M
Microbiology Glossary: M
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Microbiome
/ MY-kroh-by-ohm / · Greek mikros (small) + bios (life) + -ome (complete set)
Microbiome is the complete collection of microorganisms, their genomes, and the metabolic products they generate within a defined environment such as the human gut, skin, or soil.
The human gut microbiome contains roughly 38 trillion bacterial cells representing over 1,000 species and encodes approximately 150 times more genes than the human genome, contributing extensively to carbohydrate metabolism, immune education, and gut barrier function. Dysbiosis, an imbalance in microbiome composition, has been associated with conditions including inflammatory bowel disease, obesity, type 2 diabetes, and depression, though causal relationships remain an active area of research and correlation does not establish causation. Factors shaping the microbiome include birth mode, diet, antibiotic use, geographic location, and host genetics.
Soil microbiomes are equally rich, with a single gram of fertile agricultural soil harboring up to one billion bacterial cells from thousands of species.
Ocean microbiomes drive planetary-scale chemistry. Marine microorganisms, particularly cyanobacteria and proteobacteria, produce roughly half of Earth's atmospheric oxygen through photosynthesis and fix substantial quantities of nitrogen, linking ocean microbial communities directly to the habitability of the planet.
The microbiome is only found in the human gut. Every environment with moisture and organic matter, including skin, soil, ocean water, and plant root zones, supports its own distinct microbial community.
The human colon harbors a dense microbiome dominated by Firmicutes and Bacteroidetes, bacterial phyla that ferment dietary fiber into short-chain fatty acids such as butyrate. Butyrate concentrations in the colon typically reach 10 to 20 millimolar and supply roughly 70 percent of the energy used by colonocytes, the cells lining the colon wall.
Microorganism
/ MY-kroh-or-gan-iz-um / · Greek mikros, small; organon, instrument; ismos
Microorganism is any living entity too small to be seen with the unaided eye, including bacteria, archaea, fungi, algae, and protozoa, as well as viruses, which collectively inhabit every environment on Earth.
Microorganisms were first observed by Antonie van Leeuwenhoek in 1676 using hand-crafted microscopes achieving roughly 270-fold magnification; he called them animalcules. Collectively, they represent the majority of Earth’s biodiversity and biomass, with the total carbon stored in marine bacteria alone exceeding that of all marine plants and animals combined. Microorganisms perform global-scale biogeochemical functions including nitrogen fixation, carbon cycling, ocean primary production, and the decomposition of organic matter that recycles nutrients for all other life.
Archaea thrive in some of the most extreme environments on Earth, with species such as Pyrolobus fumarii surviving at temperatures above 113 degrees Celsius near deep-sea hydrothermal vents.
Tardigrades (Ramazzottius varieornatus) are microscopic animals, not microorganisms in the strict sense, yet they are often grouped with microbial life in ecological studies because of their size. At roughly 0.5 millimeters long, they can survive radiation doses exceeding 570,000 milligrays, a level thousands of times lethal to humans, by expressing unique DNA-protective proteins.
Yeast →All microorganisms cause disease. The vast majority of microbial species do not infect humans, and many perform indispensable ecological and industrial functions, from fermenting food to fixing atmospheric nitrogen.
Paramecium caudatum is a single-celled protozoan found in freshwater ponds and slow-moving streams worldwide. Each cell is roughly 150 to 300 micrometers long and propels itself using thousands of cilia that beat in coordinated waves, allowing it to travel approximately 1 millimeter per second.
Mycology
/ my-KOL-oh-jee / · Greek mykes, fungus; logos, study
Mycology is the scientific study of fungi, encompassing their taxonomy, physiology, biochemistry, ecology, and interactions with other organisms, including yeasts, molds, mushrooms, and their roles as decomposers, symbionts, and pathogens.
Fungi are eukaryotes with cell walls containing chitin, absorptive nutrition delivered by secreted extracellular enzymes, and reproduction by spores. They are primary decomposers in terrestrial ecosystems, forming mutualistic mycorrhizal associations with the majority of vascular plant species and causing disease in plants, animals, and immunocompromised humans. Medical mycology has grown in importance as fungal infections account for approximately 1.7 million deaths per year globally, mainly among patients with HIV/AIDS, organ transplants, or hematologic malignancies.
The field also underpins biotechnology, since the fungus Aspergillus niger produces citric acid industrially at a scale exceeding 1.6 million metric tons per year.
Penicillin, one of the most consequential medicines in history, was discovered in 1928 when Alexander Fleming noticed that the mold Penicillium notatum contaminating a bacterial culture plate had killed the surrounding Staphylococcus colonies, a mycological observation that launched the antibiotic era.
Mycology →Mycology is the study of bacteria. Mycology is exclusively the study of fungi, which are eukaryotes with chitin-containing cell walls and are no more closely related to bacteria than humans are.
Candida albicans is a yeast studied extensively in medical mycology and normally colonizes the oral cavity, gut, and vaginal mucosa of healthy humans without causing harm. When host immunity is suppressed, as in patients receiving chemotherapy, the same organism can cause invasive candidiasis with mortality rates reaching 40 percent in bloodstream infections.
Yeast →Mycorrhiza
/ my-koh-RY-zah / · Greek mykes, fungus; rhiza, root
Mycorrhiza is a mutualistic symbiotic association between a soil fungus and the roots of a vascular plant, in which the fungus receives photosynthetic sugars from the plant and in return supplies the plant with water and mineral nutrients, particularly phosphorus and nitrogen.
Arbuscular mycorrhizal fungi of the phylum Glomeromycota penetrate root cortex cells and form highly branched arbuscular structures where nutrient exchange occurs. Ectomycorrhizal fungi envelop root tips in a hyphal mantle without penetrating cells, and this type predominates among temperate forest trees such as oaks and pines. About 80 percent of all vascular plant species form mycorrhizal associations, and many forest trees cannot grow without their fungal partners, which explains why forest replanting without fungal inoculation often fails.
Mycorrhizal hyphae extend the effective absorptive surface of roots by up to 100-fold, reaching soil pores too narrow for roots to enter.
Mycorrhizal networks connecting neighboring trees of the same or different species can transfer carbon and nutrients between plants. Studies in Douglas fir (Pseudotsuga menziesii) forests have shown that older "mother trees" transfer measurable quantities of carbon-13-labeled sugars to younger seedlings through shared fungal networks.
Mycology →All fungi found on roots are harmful pathogens. Many root-associated fungi form mutualistic partnerships that improve plant survival, and the distinction between beneficial mycorrhizal fungi and harmful root pathogens depends on the specific fungal species and host plant involved.
Pine trees (Pinus sylvestris) growing in nutrient-poor boreal soils depend heavily on ectomycorrhizal fungi such as Suillus bovinus to acquire phosphorus and nitrogen. Seedlings grown in sterilized soil without fungal inoculation typically show 50 to 70 percent lower biomass after one growing season compared with inoculated seedlings in the same soil.