Editing Evolution of flagella (section)

==Bacterial flagellum==
There is good evidence that the bacterial flagellum includes and might even be based on a [[Type three secretion system|Type III secretory and transport system]], given the similarity of proteins in both systems.<ref>{{cite journal | title=Adaptivity and dynamics in type III secretion systems | vauthors=Milne-Davies B, Wimmi S, Diepold A | journal=Molecular Microbiology | volume=115 | issue=3 | pages=395–411 | date=March 2021 | pmid=33251695 | doi=10.1111/mmi.14658 | doi-access=free }}</ref>

All currently known nonflagellar Type III transport systems serve the function of exporting (injecting) [[toxins|toxin]] into eukaryotic cells.  Similarly, flagella grow by exporting [[flagellin]] through the flagellar machinery. It is hypothesised that the flagellum evolved from the type three secretory system. For example, the [[bubonic plague]] [[bacterium]] ''[[Yersinia pestis]]'' has an organelle assembly very similar to a complex flagellum, except that it is missing only a few flagellar mechanisms and functions, such as a needle to inject toxins into other cells. As such, the type three secretory system supports the hypothesis that the flagellum [[natural selection|evolved]] from a simpler [[bacterial secretion system]].

However, the true relationship could be the reverse: recent phylogenetic research strongly suggests the type three secretory system evolved from the flagellum through a series of gene deletions.<ref>{{cite journal | pmid = 23028376 | date = 2012 | last1 = Abby | first1 = S. S. | last2 = Rocha | first2 = E. P. | title = The non-flagellar type III secretion system evolved from the bacterial flagellum and diversified into host-cell adapted systems | journal = PLOS Genetics | volume = 8 | issue = 9 | pages = e1002983 | doi = 10.1371/journal.pgen.1002983 | doi-access = free | pmc = 3459982 }}</ref>

[[Reactive oxygen species]] (ROS) generated by flagellation can cause oxidative damage to DNA and are mutagenic with researchers asking "Did the innovation of a functional flagellum impact either the short- or long-term rate of bacterial evolution?".<ref name="t665">{{cite journal |last=Bhattacharyya |first=Souvik |last2=Lopez |first2=Shelby |last3=Singh |first3=Abhyudai |last4=Harshey |first4=Rasika M. |year=2024 |title=Flagellar motility is mutagenic |journal=Proceedings of the National Academy of Sciences |publisher=Proceedings of the National Academy of Sciences |volume=121 |issue=41 |page= |doi=10.1073/pnas.2412541121 |issn=0027-8424 |doi-access=free|pmc=11474059 }}</ref>

===Eubacterial flagellum ===
Eubacterial flagellum is a multifunctional organelle. It is also one of a range of motility systems in bacteria. The structure of the organelle appears like a motor, shaft and a propeller.<ref name="Young&Taner2004">Young, Matt & [[Taner Edis|Edis, Taner]] (2004). ''Why Intelligent Design Fails: A Scientific Critique of the New Creationism'' {{ISBN|0-8135-3433-X}} Rutgers University press New Brunswick, New Jersey, and London.72-84.</ref> However, the structure of eubacterial flagellae varies based on whether their motor systems run on protons or sodium, and on the complexity of the flagellar whip.<ref>Berry, R. M., and J. P. Armitage. 1999. "The Bacterial Flagella Motor." Advances in Microbial Physiology {{ISBN|978-0-12-027749-0}}. v. 49: 291–337.</ref> The evolutionary origin of eubacterial flagellae is probably an example of indirect evolution. A hypothesis on the evolutionary pathway of the eubacterial flagellum argues that a secretory system evolved first, based around the SMC rod- and pore-forming complex. This is presumed to be the common ancestor of the type-III secretory system and the flagellar system. Then, an ion pump was introduced to this structure which improved secretion. The ion pump later became the motor protein. This was followed by the emergence of the proto-flagellar filament as part of the protein-secretion structure. Gliding-twitching motility arose at this stage or later and was then refined into swimming motility.<ref name="Young&Taner2004"/>