Editing Chemotaxis (section)

=== Behavior ===
The overall movement of a bacterium is the result of alternating tumble and swim phases, called [[run-and-tumble motion]].<ref>{{cite journal | vauthors = Berg HC, Brown DA | s2cid = 1909173 | title = Chemotaxis in Escherichia coli analysed by Three-dimensional Tracking | journal = Nature | volume = 239 | issue = 5374 | pages = 500–504 | date = October 1972 | doi = 10.1038/239500a0 | pmid = 4563019 | bibcode = 1972Natur.239..500B }}</ref> As a result, the trajectory of a bacterium swimming in a uniform environment will form a [[random walk]] with relatively straight swims interrupted by random tumbles that reorient the bacterium.<ref>{{cite journal | vauthors = Sourjik V, Wingreen NS | title = Responding to chemical gradients: bacterial chemotaxis | journal = Current Opinion in Cell Biology | volume = 24| issue = 2| pages = 262–268 | date = April 2012 | doi = 10.1016/j.ceb.2011.11.008 | pmid = 22169400 | pmc = 3320702 }}</ref> Bacteria such as ''[[Escherichia coli|E. coli]]'' are unable to choose the direction in which they swim, and are unable to swim in a straight line for more than a few seconds due to rotational [[diffusion]]; in other words, bacteria "forget" the direction in which they are going. By repeatedly evaluating their course, and adjusting if they are moving in the wrong direction, bacteria can direct their random walk motion toward favorable locations.<ref>{{cite book| vauthors = Berg HC |title=Random walks in biology|year=1993|pages=83–94|publisher=Princeton Univ. Press|location=Princeton, NJ|isbn=978-0-691-00064-0|edition=Expanded, rev.}}</ref>

In the presence of a chemical [[gradient]] bacteria will chemotax, or direct their overall motion based on the gradient. If the bacterium senses that it is moving in the correct direction (toward attractant/away from repellent), it will keep swimming in a straight line for a longer time before tumbling; however, if it is moving in the wrong direction, it will tumble sooner. Bacteria like ''[[Escherichia coli|E. coli]]'' use temporal sensing to decide whether their situation is improving or not, and in this way, find the location with the highest concentration of attractant, detecting even small differences in concentration.<ref>{{cite journal |vauthors= Sourjik V, Wingreen N|date=April 2012|title=Responding to Chemical Gradients: Bacterial Chemotaxis |journal= Current Opinion in Cell Biology|volume=24 |issue= 2|pages=262–8|doi=10.1016/j.ceb.2011.11.008|pmid= 22169400|pmc=3320702}}</ref>

This biased random walk is a result of simply choosing between two methods of random movement; namely tumbling and straight swimming.<ref>{{cite journal | vauthors = Macnab RM, Koshland DE | title = The gradient-sensing mechanism in bacterial chemotaxis | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 69 | issue = 9 | pages = 2509–2512 | date = September 1972 | pmid = 4560688 | pmc = 426976 | doi = 10.1073/pnas.69.9.2509 | doi-access = free | bibcode = 1972PNAS...69.2509M }}</ref> The helical nature of the individual flagellar filament is critical for this movement to occur. The protein structure that makes up the flagellar filament, [[flagellin]], is conserved among all flagellated bacteria.<ref>{{cite journal | vauthors = Nedeljković M, Sastre DE, Sundberg EJ | title = Bacterial Flagellar Filament: A Supramolecular Multifunctional Nanostructure | journal = International Journal of Molecular Sciences | volume = 22 | issue = 14 | pages = 7521 | date = July 2021 | pmid = 34299141 | pmc = 8306008 | doi = 10.3390/ijms22147521 | doi-access = free }}</ref> Vertebrates seem to have taken advantage of this fact by possessing an immune receptor ([[Toll-like receptor|TLR5]]) designed to recognize this conserved protein.<ref>{{cite journal | vauthors = Zhong M, Yan H, Li Y | title = Flagellin: a unique microbe-associated molecular pattern and a multi-faceted immunomodulator | journal = Cellular & Molecular Immunology | volume = 14 | issue = 10 | pages = 862–864 | date = October 2017 | pmid = 28845044 | pmc = 5649114 | doi = 10.1038/cmi.2017.78 }}</ref>

As in many instances in biology, there are bacteria that do not follow this rule. Many bacteria, such as ''Vibrio'', are monoflagellated and have a single flagellum at one pole of the cell. Their method of chemotaxis is different. Others possess a single flagellum that is kept inside the cell wall. These bacteria move by spinning the whole cell, which is shaped like a corkscrew.<ref>{{cite book | vauthors = Berg HC | title=''E. coli'' in motion | year=2003 | isbn = 978-0-387-00888-2 |publisher=Springer | location=New York, NY }}{{page needed|date=March 2017}}</ref>{{page needed|date=March 2017}}