BIO-Complexity, Vol 2021

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An Engineering Perspective on the Bacterial Flagellum: Part 3 – Observations

Waldean A Schulz


The flagellum is the organelle imparting motility to common bacteria. This paper, the third of three, takes a systems engineering and systems biology perspective on the bacterial flagellum. The first paper (Part 1 of the series) provided a constructive or top-down view from a systems engineering viewpoint. It detailed the typical environment, the purpose, the required existing and new resources, the necessary functional requirements, the various constraints, the control means, and the self-assembly for any kind of bacterial motility organelle. The specification of these requirements was intended to be independent of knowledge about the actual flagellum. A converse approach was detailed in the second paper (Part 2 of the series). It was an analytical or bottom-up view, which discussed the known 40+ protein components and the observed and inferred structure, control, and assembly of a typical bacterial flagellum. This cellular subsystem is well researched. Much of that research was reviewed in Part 2 from a systems biology viewpoint, including the chemotaxis feedback control system. Part 2 included a very detailed dependency graph of the orchestrated assembly not found elsewhere. This third paper (Part 3) concludes the three-part study with original observations. The observations include an ontology of the exceedingly specific protein binding relationships in the flagellum. The latter observation is new and significant and suggests research to further elaborate the details of the molecular configurations of the proteins. Part 3 also compares the independent constructive and analytical views, which correlate well. Finally, it is suggested that a motility organelle of this scope and scale seems profoundly unlikely to naturally evolve in the absence of foresight and mindful intent.

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