Microaerophile

{{Short description|Microorganism requiring lower levels of oxygen than normally found in atmosphere}} [[Image:Anaerobic.png|300px|thumb|right|Anaerobic bacteria can be identified by growing them in test tubes of thioglycollate broth: 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. 2: Obligate anaerobes are poisoned by oxygen, so they gather at the bottom of the tube where the oxygen concentration is lowest. 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. 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. 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. ]]

A '''microaerophile''' is a microorganism that requires environments containing lower levels of dioxygen than those present in the atmosphere (i.e. < 21% O2; typically 2–10% O2) for optimal growth.<ref name=Fuduche/> A more restrictive interpretation requires the microorganism to be obligate in this requirement.<ref name=Hogg>{{cite book |author=Hogg, S. |title=Essential Microbiology| publisher = Wiley |year=2005 |edition=1st |pages=91–107| isbn = 0-471-49754-1}}</ref><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> Many microaerophiles are also capnophiles, requiring an elevated concentration of carbon dioxide (e.g. 10% CO2 in the case of ''Campylobacter'' species).<ref name=JMA>{{cite book |vauthors=Brooks GF, Carroll KC, Butel JS, Morse SA |title=Jawetz, Melnick & Adelberg's Medical Microbiology |url=https://archive.org/details/jawetzmelnickade00broo_450 |url-access=limited |publisher = McGraw Hill |year=2007 |edition=24th |pages=[https://archive.org/details/jawetzmelnickade00broo_450/page/n274 273]–275| isbn = 978-0-07-128735-7 }}</ref>

The original definition of a ''microaerophile'' has been criticized for being too restrictive and not accurate enough compared to similar categories. The broader term '''microaerobe''' has been coined to describe microbes ''able'' to respire oxygen "within microoxic environments by using high-affinity terminal oxidase".<ref name=Fuduche>{{cite journal |last1=Fuduche |first1=Maxime |last2=Davidson |first2=Sylvain |last3=Boileau |first3=Céline |last4=Wu |first4=Long-Fei |last5=Combet-Blanc |first5=Yannick |title=A Novel Highly Efficient Device for Growing Micro-Aerophilic Microorganisms |journal=Frontiers in Microbiology |date=19 March 2019 |volume=10 |pages=534 |doi=10.3389/fmicb.2019.00534|pmid=31001208 |pmc=6434946 |doi-access=free }}</ref>

==Culture== Microaerophiles are traditionally cultivated in candle jars. Candle jars are containers into which a lit candle is introduced before sealing the container's airtight lid. The candle's flame burns until extinguished by oxygen deprivation, creating a carbon dioxide-rich, oxygen-poor atmosphere.<ref name="pmid24399385">{{cite journal |vauthors=Salim SM, Mandal J, Parija SC |title=Isolation of ''Campylobacter'' from human stool samples|journal=Indian J Med Microbiol |volume=32 |issue=1 |pages=35–38 |date= March 2014 |pmid=24399385 |doi= 10.4103/0255-0857.124294|doi-access=free }}</ref>

Newer oxystat bioreactor methods allow for more precise control of gas levels in the microaerobic environment, using a probe to measure the oxygen concentration or redox potential in real time.<ref>{{cite journal |last1=Liu |first1=Chen-Guang |last2=Xue |first2=Chuang |last3=Lin |first3=Yen-Han |last4=Bai |first4=Feng-Wu |title=Redox potential control and applications in microaerobic and anaerobic fermentations |journal=Biotechnology Advances |date=March 2013 |volume=31 |issue=2 |pages=257–265 |doi=10.1016/j.biotechadv.2012.11.005|pmid=23178703 }}</ref> Ways to control oxygen intake include gas-generating packs and gas exchange.<ref name="JMA"/>

As oxystat bioreactors are expensive to buy and run, lower-cost solutions have been devised. For example, the Micro-Oxygenated Culture Device (MOCD) is a system involving ordinary flasks, oxygen-permeable tubes, sensors, and water pumps. Aeration is done by pumping the culture medium through the tubes.<ref name=Fuduche/>

==Examples== A wide variety of microaerobic conditions exist in the world: in human bodies, underwater, etc. Many bacteria from these sources are microaerobes, some of which are also microaerophiles. * Some members of Campylobacterales are microaerophilic: ** ''Campylobacter'' species are microaerophilic.<ref name="JMA"/><ref name="pmid330861">{{cite journal |vauthors=Fernie DS, Park RW |title=The isolation and nature of campylobacters (microaerophilic vibrios) from laboratory and wild rodents |journal=J. Med. Microbiol. |volume=10 |issue=3 |pages=325–9 |date=August 1977 |pmid=330861 |doi= 10.1099/00222615-10-3-325|doi-access=free }}</ref> ** ''Helicobacter pylori'' (previously identified as a ''Campylobacter''), a species of Campylobacterota that has been linked to peptic ulcers and some types of gastritis<ref name="pmid23015486">{{cite book |author=Cover TL|title=Perspectives on methodology for ''in vitro'' culture of ''Helicobacter pylori'' |chapter=Perspectives on Methodology for in Vitro Culture of Helicobacter pylori |series=Methods Mol Biol |volume=921 |pages=11–15 |year=2012 |pmid=23015486 |doi=10.1007/978-1-62703-005-2_3 |pmc=3921885|isbn=978-1-62703-004-5 }}</ref> * Many members of ''Lactobacillus'' sensu lato (see Lactobacillaceae) are microaerophiles. As facultative anaerobes, they do survive anaerobic conditions, but grow better with a little oxygen.<ref>{{cite journal |last1=Goldstein |first1=Ellie J. C. |last2=Tyrrell |first2=Kerin L. |last3=Citron |first3=Diane M. |title=Lactobacillus Species: Taxonomic Complexity and Controversial Susceptibilities |journal=Clinical Infectious Diseases |date=15 May 2015 |volume=60 |issue=suppl_2 |pages=S98–S107 |doi=10.1093/cid/civ072|pmid=25922408 |doi-access=free }}</ref> * ''Magnetospirillum gryphiswaldense'' and ''Magnetospira'' sp. QH-2 are aquatic microaerophilic magnetotactic bacteria. The formation of magnetite in such bacteria in general require microaerobic conditions.<ref name=Fuduche/>

==References== {{reflist}}

==External links== * [https://archive.today/20130801122104/http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=3343302 Characterization of an unclassified microaerophilic bacterium associated with gastroenteritis.]

Category:Microbial growth and nutrition