Magnetotaxis

{{Short description|Bacteria movement with Earth's magnetic field}} {{Use dmy dates|date=April 2022}} '''Magnetotaxis''' is a process implemented by a diverse group of Gram-negative bacteria that involves orienting and coordinating movement in response to Earth's magnetic field.<ref name="one">{{cite journal|last1=Lefevre|first1=C. T.|last2=Bazylinski|first2=D. A.|title=Ecology, Diversity, and Evolution of Magnetotactic Bacteria|journal=Microbiology and Molecular Biology Reviews|date=4 September 2013|volume=77|issue=3|pages=497–526|doi=10.1128/MMBR.00021-13|pmid=24006473|pmc=3811606}}</ref> This process is mainly carried out by microaerophilic and anaerobic bacteria found in aquatic environments such as salt marshes, seawater, and freshwater lakes.<ref name="three">{{cite journal|last1=Yan|first1=Lei|last2=Zhang|first2=Shuang|last3=Chen|first3=Peng|last4=Liu|first4=Hetao|last5=Yin|first5=Huanhuan|last6=Li|first6=Hongyu|title=Magnetotactic bacteria, magnetosomes and their application|journal=Microbiological Research|date=October 2012|volume=167|issue=9|pages=507–519|doi=10.1016/j.micres.2012.04.002|pmid=22579104|doi-access=free}}</ref> By sensing the magnetic field, the bacteria are able to orient themselves towards environments with more favorable oxygen concentrations. This orientation towards more favorable oxygen concentrations allows the bacteria to reach these environments faster as opposed to random movement through Brownian motion.<ref name="four">{{cite journal|last1=Smith|first1=M.J.|last2=Sheehan|first2=P.E.|last3=Perry|first3=L.L.|last4=O’Connor|first4=K.|last5=Csonka|first5=L.N.|last6=Applegate|first6=B.M.|last7=Whitman|first7=L.J.|title=Quantifying the Magnetic Advantage in Magnetotaxis|journal=Biophysical Journal|date=August 2006|volume=91|issue=3|pages=1098–1107|doi=10.1529/biophysj.106.085167|pmid=16714352|bibcode=2006BpJ....91.1098S|pmc=1563769}}</ref>

== Overview == Magnetic bacteria (e.g. ''Magnetospirillum magnetotacticum'') contain internal structures known as magnetosomes which are responsible for the process of magnetotaxis. After orienting to the magnetic field using the magnetosomes, the bacteria use flagella to swim along the magnetic field, towards the more favorable environment.<ref name="two">{{cite journal |last1=Frankel |first1=Richard B |date=2003 |title=Biological Permanent Magnets |url=https://digitalcommons.calpoly.edu/phy_fac/109 |journal=Hyperfine Interactions |volume=151 |issue=1 |pages=145–153 |bibcode=2003HyInt.151..145F |doi=10.1023/B:HYPE.0000020407.25316.c3|s2cid=41997803 |url-access=subscription }}</ref> Magnetotaxis has no impact on the average speed of the bacteria.<ref name="four" /> However, magnetotaxis allows bacteria to guide their otherwise random movement. This process is similar in practice to aerotaxis, but governed by magnetic fields instead of oxygen concentrations.<ref>{{Citation |last1=Bennet |first1=Mathieu A. |title=Magnetoreception and Magnetotaxis |date=2016-07-05 |url=https://onlinelibrary.wiley.com/doi/10.1002/9783527691395.ch22 |work=Iron Oxides |pages=567–590 |editor-last=Faivre |editor-first=Damien |edition=1 |publisher=Wiley |language=en |doi=10.1002/9783527691395.ch22 |isbn=978-3-527-33882-5 |access-date=2022-04-24 |last2=Eder |first2=Stephan H. K.|url-access=subscription }}</ref> Magnetotaxis and aerotaxis often function together, as bacteria can use both magnetotactic and aerotactic systems to find proper oxygen concentrations. This is referred to as magneto-aerotaxis.<ref name=":0">{{Cite book |title=Encyclopedia of microbiology |date=2009 |publisher=Elsevier |others=Moselio Schaechter |isbn=978-0-12-373944-5 |edition=3rd |location=[Amsterdam] |oclc=399645273}}</ref> By orienting towards the Earth's poles, marine bacteria are able to direct their movement downwards, towards the anaerobic/micro aerobic sediments. This allows bacteria to change metabolic environments, which can enable chemical cycles.<ref>{{Cite journal |last1=Li |first1=Jinhua |last2=Liu |first2=Peiyu |last3=Wang |first3=Jian |last4=Roberts |first4=Andrew P. |last5=Pan |first5=Yongxin |date=December 2020 |title=Magnetotaxis as an Adaptation to Enable Bacterial Shuttling of Microbial Sulfur and Sulfur Cycling Across Aquatic Oxic-Anoxic Interfaces |url=https://onlinelibrary.wiley.com/doi/10.1029/2020JG006012 |journal=Journal of Geophysical Research: Biogeosciences |language=en |volume=125 |issue=12 |doi=10.1029/2020JG006012 |bibcode=2020JGRG..12506012L |s2cid=228886950 |issn=2169-8953|url-access=subscription }}</ref>

== Magnetosomes == Magnetosomes contain crystals - often magnetite (Fe₃O₄).<ref>{{Cite journal |last1=Lower |first1=Brian H. |last2=Bazylinski |first2=Dennis A. |date=2013 |title=The Bacterial Magnetosome: A Unique Prokaryotic Organelle |url=https://www.karger.com/Article/FullText/346543 |journal=Journal of Molecular Microbiology and Biotechnology |language=en |volume=23 |issue=1–2 |pages=63–80 |doi=10.1159/000346543 |pmid=23615196 |s2cid=25856024 |issn=1660-2412|url-access=subscription }}</ref> Some extremophile bacteria from sulfurous environments have been isolated with greigite (an iron-sulfide compound Fe₃S₄).<ref name="five">{{cite book |last1=Dusenbery |first1=David B. |title=Living at micro scale : the unexpected physics of being small |date=2009 |publisher=Harvard University Press |isbn=9780674031166 |location=Cambridge, Mass.}}</ref> Some magnetotactic bacteria also contain pyrite (FeS₂) crystals, possibly as a transformation product of greigite.<ref>{{cite journal|journal=Nature|title=Biomineralization of ferrimagnetic greigite (Fe₃S₄) and iron pyrite (FeS₂) in a magnetotactic bacterium|last1=Mann|first1=Stephen|volume=343|issue=6255|pages=258–261|url=https://www.nature.com/articles/343258a0|publication-date=18 January 1990|year=1990|last2=Sparks|first2=Nicholas H. C.|last3=Frankel|first3=Richard B.|last4=Bazylinski|first4=Dennis A.|last5=Jannasch|first5=Holger W.|doi=10.1038/343258a0|bibcode=1990Natur.343..258M |s2cid=4351424 |display-authors=3|url-access=subscription}} </ref> These crystals are contained within a bilayer membrane called the magnetosome membrane which is embedded with specific proteins. There are many different shapes of crystals. Crystal shape is typically consistent within a bacterial species.<ref name="three" /> The most common arrangement of magnetosomes is in chains which allows a maximum magnetic dipole moment to be created.<ref name="one" /> Within bacteria, there can be many chains of magnetosomes of different lengths that tend to align along the long axis of bacterial cell.<ref name="two" /> The dipole moment created from the chains of magnetosomes allows the bacteria to align with the magnetic field as they move.<ref name="one" /> Once magnetic bacteria die, they are able to orient themselves to the Earth's magnetic field but they are incapable of migrating along the field.<ref name="two" />

== Hemispheres and magnetic fields == In the northern hemisphere, north-seeking bacteria move downwards towards sediment (parallel to the magnetic field). In the southern hemisphere, south seeking bacteria dominate and move downwards toward the sediment (antiparallel to the magnetic field).<ref name=":0" /> It was originally thought by scientists that south seeking bacteria would move upwards in the north hemisphere, towards very high concentrations of oxygen. This would negatively select south seeking bacteria; so that north seeking bacteria dominate in the northern hemisphere and vice versa. However, south-seeking bacteria have been found in the northern hemisphere. Additionally, both north and south seeking magnetic bacteria, are found even at the Earth's magnetic equator, where the field is directed horizontally.<ref name="one" />

==See also== * Magnetoception * Magnetotactic bacteria

==Notes and references== {{reflist}}

==Further reading== *{{cite book|last1=Odenwald|first1=Sten|title=The 23rd Cycle|url=https://archive.org/details/23rdcyclelearnin00oden|url-access=registration|date=March 15, 2002|publisher=Columbia University Press|isbn=978-0231120791|pages=[https://archive.org/details/23rdcyclelearnin00oden/page/57 57]&ndash;62}}

==External links== * [http://www.calpoly.edu/~rfrankel/magbac101.html Magnetotaxis in bacteria] * [http://www.astronomycafe.net/qadir/ask/a11651.html Do animals really use magnetism in any interesting way to navigate?] (The Astronomy Cafe)

{{Taxes (Biology)}}

Category:Magnetoreception Category:Taxes (biology)