Microbiology Terms Starting With U
Microbiology Glossary: U
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Ubiquitous Microbe
/ yoo-BIK-wih-tus MY-krohb / · Latin ubique (everywhere) + Greek mikros (small) + bios (life)
Ubiquitous Microbe is a microorganism found in virtually all environments examined, including soil, water, air, extreme habitats, and in and on the bodies of all multicellular organisms.
Pseudomonas aeruginosa exemplifies microbial ubiquity: it thrives in soil, freshwater, hospital surfaces, and the airways of immunocompromised patients, tolerating temperatures from 4°C to 42°C and a broad range of pH. Its small cell size, typically 1 to 5 micrometers, and rapid doubling time of roughly 40 minutes under favorable conditions allow populations to establish in newly formed habitats with little delay. Efficient dispersal by air currents, water flow, and animal movement carries microbial cells across continents, explaining why the same species appear in geographically distant soils.
This near-universal presence means microbes underpin every major biogeochemical cycle, from carbon and nitrogen fixation to sulfur and phosphorus turnover.
Bacillus subtilis spores collected from the stratosphere at altitudes above 20 kilometers demonstrate that microbial dispersal reaches far beyond the surface biosphere, with viable cells recovered from air samples taken over the open Pacific Ocean.
Ubiquitous microbes are dangerous because of their widespread distribution. Most ubiquitous microbes are free-living environmental organisms that rarely cause disease in healthy hosts.
Pseudomonas fluorescens colonizes the surfaces of plant roots in soils worldwide, including Antarctic soils where temperatures remain near 0°C for most of the year. Researchers have recovered viable populations from soils separated by more than 10,000 kilometers, with cell densities reaching 10 million colony-forming units per gram of rhizosphere soil.
Urease
/ YOOR-ee-ase / · From Greek ouron, meaning urine, with suffix -ase indicating an enzyme.
Urease is a nickel-containing enzyme that catalyzes the hydrolysis of urea into ammonia and carbon dioxide.
Each active site of urease requires two nickel ions and can catalyze roughly 10,000 reactions per second, making it one of the fastest known metalloenzymes. Helicobacter pylori (H. pylori) depends on urease to survive the acidic stomach environment: the ammonia produced neutralizes gastric acid immediately around the bacterium, allowing it to colonize the gastric mucosa and contribute to peptic ulcer disease in an estimated 10 percent of infected individuals.
Proteus mirabilis produces urease at particularly high levels during urinary tract infections, where ammonia generation raises urine pH and causes calcium and magnesium phosphate to precipitate as struvite kidney stones. Clinically, a positive urease test, detected by color change in urea-containing media, helps microbiologists distinguish urease-positive genera such as Proteus and Helicobacter from urease-negative pathogens.
Urease was the first enzyme ever crystallized, a feat accomplished by James Sumner at Cornell University in 1926. That achievement provided the first direct evidence that enzymes are proteins and earned Sumner the Nobel Prize in Chemistry in 1946.
Urease only benefits bacteria living in acidic environments. The enzyme also supports nitrogen scavenging from urea in nitrogen-poor soils and contributes to kidney stone formation in alkaline urinary tract infections caused by Proteus mirabilis.
Clinical microbiology laboratories use the rapid urease test, sometimes called the CLO test, to detect Helicobacter pylori from gastric biopsy specimens within minutes rather than the days required for culture. A biopsy is placed in a urea-containing medium with a pH indicator, and a color change from yellow to pink within 2 to 24 hours signals that any urease-positive Helicobacter in the sample has split urea into ammonia, raising the local pH and revealing the infection without the need for slow conventional identification.