Microaerophiles are microorganisms that require oxygen for growth but at concentrations lower than those found in the atmosphere.
Explanation
Microaerophiles are aerobic organisms that have adapted to live in environments where oxygen is present but at concentrations substantially lower than the ~21 % found in air. Typically they grow best at O2 levels of 2–10 %, and they are damaged or killed by atmospheric oxygen. Their limited capacity to detoxify reactive oxygen species such as superoxide and hydrogen peroxide necessitates lower oxygen exposure. Many microaerophiles also require elevated concentrations of carbon dioxide, reflecting their natural habitats.
In the laboratory, microaerophiles are distinguished by their growth pattern in thioglycollate or semi‑solid oxygen gradient media: they form a band of growth just below the surface where oxygen diffusion has been partially depleted. To cultivate them, microaerobic conditions can be created using candle jars, chemical gas‑generating sachets or controlled gas mixtures. Ecologically, microaerophiles occupy niches where oxygen tension is reduced, such as sediments, deep water columns, soil aggregates, biofilms and the mucosal surfaces of animals. Human pathogens including Helicobacter pylori, which colonizes the stomach, and Campylobacter jejuni, a common cause of gastroenteritis, are microaerophilic. Other examples include some species of Spirillum and Vibrio. By thriving at the interface between oxic and anoxic zones, microaerophiles play roles in nitrogen and sulfur cycling. Understanding their oxygen requirements is important for isolation, identification and management of microaerophilic pathogens.
Characteristics and Examples
- Require 2–10 % oxygen and often elevated CO2 for optimal growth; atmospheric oxygen inhibits or kills them.
- Grow as a tight band in thioglycollate broth where oxygen concentration matches their preference.
- Examples: Helicobacter pylori, Campylobacter jejuni, Microaerobacter aerodenitrificans, and some Vibrio species.
- Microaerophilic conditions are generated using candle jars, gas‑pack systems or incubators with precise gas control.
Microaerophiles occupy ecological and clinical niches where low oxygen tension is maintained. Cultivating and studying them requires special gas mixtures, but understanding their physiology is important for food safety, infectious disease and environmental microbiology.
Related Terms: Aerotolerant, Obligate Aerobe, Facultative Anaerobe, Capnophile, Oxygen Gradient