Editing Obligate aerobe

{{Short description|Organism that requires oxygen to grow}}
[[Image:Anaerobic.png|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 anaerobe]]s 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: [[Microaerophile]]s 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.<ref name=PHK>{{cite book |vauthors=Prescott LM, Harley JP, Klein DA |title=Microbiology |publisher = Wm. C. Brown Publishers |year=1996 |edition=3rd |pages=130–131| isbn = 0-697-29390-4}}</ref>  Through [[cellular respiration]], these organisms use oxygen to metabolise substances, like sugars or fats, to obtain energy.<ref name="PHK" /><ref name=":0" /> In this type of respiration, oxygen serves as the terminal electron acceptor for the [[electron transport chain]].<ref name="PHK"/>  [[Aerobic respiration]] has the advantage of yielding more energy ([[Adenosine triphosphate|adenosine triphosphate or ATP]]) than [[fermentation]] or [[anaerobic respiration]],<ref name=Hogg>{{cite book |author=Hogg, S. |title=Essential Microbiology| publisher = Wiley |year=2005 |edition=1st |pages=99–100, 118–148| isbn = 0-471-49754-1}}</ref> but obligate aerobes are subject to high levels of [[oxidative stress]].<ref name=":0">"Obligate aerobe - definition from Biology-Online.org." ''Biology Online.'' Biology-Online, n.d. Web. 12 Dec 2009. <http://www.biology-online.org/dictionary/Obligate_aerobe></ref>
{| class="wikitable"
|+Table 1. Terms used to describe O<sub>2</sub> Relations of Microorganisms.<ref>{{Cite web|last=WI|first=Kenneth Todar, Madison|title=Nutrition and Growth of Bacteria|url=http://textbookofbacteriology.net/nutgro_4.html|access-date=2021-04-20|website=textbookofbacteriology.net}}</ref>
! 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|Obligate Anaerobe]]
|No growth
|Growth
|Toxic
|-
|[[Facultative anaerobic organism|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|Aerotolerant Anaerobe]]
|Growth
|Growth
|Not required and not used
|}

== Examples ==
Among organisms, almost all animals, most [[Fungus|fungi]], and several [[bacteria]] are obligate aerobes.<ref name=":0" /> Examples of obligately aerobic bacteria include ''[[Mycobacterium tuberculosis]]'' ([[Acid-fastness|acid-fast]]),<ref name=":0" /><ref name="Levinson, W. 2010 150-157">{{cite book |author=Levinson, W. |title=Review of Medical Microbiology and Immunology| publisher = McGraw-Hill |year=2010 |edition=11th |pages=150–157| isbn = 978-0-07-174268-9}}</ref> ''[[Bacillus]]'' ([[Gram-positive bacteria|Gram-positive]]),<ref name=":0" /> and ''[[Nocardia asteroides]]'' ([[Gram-positive bacteria|Gram-positive]]).<ref name=":0" /><ref name="Sherris">{{cite book | editor = Ryan KJ | editor2 = Ray CG | title = Sherris Medical Microbiology | edition = 4th | publisher = McGraw Hill | year = 2004 | pages= 460–462| isbn = 0-8385-8529-9 }}</ref>  With the exception of the [[yeasts]], most [[fungus|fungi]] are obligate aerobes.<ref name="PHK" />  Also, almost all [[algae]] are obligate aerobes.<ref name="PHK" />

A unique obligate aerobe is ''[[Streptomyces coelicolor]]'' which is [[Gram-positive bacteria|gram-positive]], soil-dwelling, and belongs to the [[phylum]] [[Actinomycetota]].<ref name=":1">{{Cite journal|last1=Fischer|first1=Marco|last2=Alderson|first2=Jesse|last3=van Keulen|first3=Geertje|last4=White|first4=Janet|last5=Sawers|first5=R. GaryYR 2010|title=The obligate aerobe Streptomyces coelicolor A3(2) synthesizes three active respiratory nitrate reductases|journal=Microbiology|year=2010|volume=156|issue=10|pages=3166–3179|doi=10.1099/mic.0.042572-0|pmid=20595262|issn=1465-2080|doi-access=free}}</ref> It is unique because the [[genome]] of this obligate aerobe encodes numerous [[Enzyme|enzymes]] with functions that are usually attributed to [[anaerobic metabolism]] in facultatively and strictly [[anaerobic bacteria]].<ref name=":1" />

== Survival strategies ==
When obligate aerobes are in a temporarily oxygen-deprived environment, they need survival strategies to avoid death.<ref name=":2">{{Cite journal|last1=Berney|first1=Michael|last2=Greening|first2=Chris|last3=Conrad|first3=Ralf|last4=Jacobs|first4=William R.|last5=Cook|first5=Gregory M.|date=2014-08-05|title=An obligately aerobic spirillum fermentative hydrogen production to survive reductive stress during hypoxia|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=111|issue=31|pages=11479–11484|doi=10.1073/pnas.1407034111|issn=0027-8424|pmc=4128101|pmid=25049411|bibcode=2014PNAS..11111479B|doi-access=free}}</ref> 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]].<ref name=":2" /> This example is the first time that [[hydrogen production]] has been seen in an obligate aerobe.<ref name=":2" /> It also confirms the [[fermentation]] in a [[mycobacterium]] and is evidence that hydrogen plays a role in survival as well as growth.<ref name=":2" />

Problems can also arise in oxygen-rich environments, most commonly attributed to [[oxidative stress]]. This occurrence is when there is an imbalance of [[free radicals]] and [[Antioxidant|antioxidants]] in the cells of the organism, largely due to [[pollution]] and [[radiation]] in the environment. Obligate aerobes survive this [[phenomenon]] by using the organism's [[immune system]] to correct the imbalance.<ref>{{Cite web|date=2019-04-03|title=What is oxidative stress? Effects on the body and how to reduce|url=https://www.medicalnewstoday.com/articles/324863|access-date=2021-05-08|website=www.medicalnewstoday.com|language=en}}</ref>

== See also ==
* [[Aerobic respiration]]
* [[Anaerobic respiration]]
* [[Fermentation]]
* [[Obligate anaerobe]]
* [[Facultative anaerobic organism|Facultative anaerobe]]
* [[Microaerophile]]

== References ==
{{Reflist}}

{{Bacteria}}

{{DEFAULTSORT:Obligate Aerobe}}
[[Category:Microbiology]]


{{Microbiology-stub}}