300px|thumb|Aerobic and anaerobic [[bacteria can be identified by growing them in test tubes of thioglycollate broth: <br /> 1: Obligate aerobes need oxygen because they cannot ferment or respire anaerobically. They gather at the top of the tube where the oxygen concentration is highest. <br /> 2: Obligate anaerobes are poisoned by oxygen, so they gather at the bottom of the tube where the oxygen concentration is lowest. <br /> 3: Facultative anaerobes can grow with or without oxygen because they can metabolise energy aerobically or anaerobically. They gather mostly at the top because aerobic respiration generates more ATP than either fermentation or anaerobic respiration. <br /> 4: Microaerophiles need oxygen because they cannot ferment or respire anaerobically. However, they are poisoned by high concentrations of oxygen. They gather in the upper part of the test tube but not the very top. <br /> 5: Aerotolerant organisms do not require oxygen as they metabolise energy anaerobically. Unlike obligate anaerobes however, they are not poisoned by oxygen. They can be found evenly spread throughout the test tube. ]]
An obligate aerobe is an organism that requires oxygen to grow. Through cellular respiration, these organisms use oxygen to metabolise substances, like sugars or fats, to obtain energy. but obligate aerobes are subject to high levels of oxidative stress.
{| class="wikitable"
|+Table 1. Terms used to describe O<sub>2</sub> Relations of Microorganisms.
! rowspan="2" |Group
! colspan="2" |Environment
! rowspan="2" |O<sub>2</sub> Effect
|-
!Aerobic
!Anaerobic
|-
|Obligate Aerobe
|Growth
|No growth
|Required (used for aerobic respiration)
|-
|Obligate Anaerobe
|No growth
|Growth
|Toxic
|-
|Facultative Anaerobe (Facultative Aerobe)
|Growth
|Growth
|Not required for growth but used when available
|-
|Microaerophile
|Growth if level is not too high
|No growth
|Required but at levels below 0.2 atm
|-
|Aerotolerant Anaerobe
|Growth
|Growth
|Not required and not used
|}
Examples
Among organisms, almost all animals, most fungi, and several bacteria are obligate aerobes. Bacillus (Gram-positive), With the exception of the yeasts, most fungi are obligate aerobes. It is unique because the genome of this obligate aerobe encodes numerous enzymes with functions that are usually attributed to anaerobic metabolism in facultatively and strictly anaerobic bacteria. Under these conditions, Mycobacterium smegmatis can quickly switch between fermentative hydrogen production and hydrogen oxidation with either oxygen or fumarate reduction depending on the availability of electron acceptor.
See also
- Aerobic respiration
- Anaerobic respiration
- Fermentation
- Obligate anaerobe
- Facultative anaerobe
- Microaerophile