Abstract
Cilia and flagella are organelles of motility that enable cells to swim or move liquid over its surface. An exhaustive literature survey for the presence of the organelle in organisms across phyla showed that most animal cells harbor cilia in contrast to very few fungal cells. While this was not unexpected, it was the position and arrangement of this organelle in each cell that intrigued our attention. Natural selection might have favored motility over chemotaxis; and it would have done so to evolve a stable structure that could have undergone an optimization process requiring a precise geometry in the shape of cells and the structure that would help cells to move. The positioning of such a structure would play a pre-dominant role in optimal motility. It is now known that the flagellar position of a cell is a genetically distinct trait, occasionally used in phylogeny of bacteria, distributed in distinguishing patterns over cellular surface, but basically are of two types, either polar (one flagellum arising from one pole per cell) or peritrichous (lateral flagella distributed over the entire cell surface). Irrespective of the cellular habitat, flagella origin, ultrastructure and proteome, the present investigation surveyed 26 sub-types of flagellar arrangements from as many species as possible. A peculiar pattern ensued-Prokaryotes harbored predominantly polar and peritrichous types; eukaryotes showed a mere change of the peritrichous one. These numbers when used to create a Similarity tree depicted a similarity distance of 14 between the Eubacteria and Archaebacteria forming the first neighborhood; Protozoans, Algae, Fungi, Plantae and Animalia formed a second neighborhood. We offer a working hypothesis for this pattern and the gradual shift in the flagellar arrangement from polar, peritrichous, sub-apical, and apical to lateral throughout evolution.
Highlights
Most organisms modulate their motility in response to environmental variables such as nutrients, abiotic and biotic stress [1,2]
It is known that the flagellar position of a cell is a genetically distinct trait, occasionally used in phylogeny of bacteria, distributed in distinguishing patterns over cellular surface, but basically are of two types, either polar or peritrichous
We offer a working hypothesis for this pattern and the gradual shift in the flagellar arrangement from polar, peritrichous, sub-apical, and apical to lateral throughout evolution
Summary
Most organisms modulate their motility in response to environmental variables such as nutrients, abiotic and biotic stress [1,2]. The once vestigial organelle, the flagellum, and its evolution is of enormous interest to biologists because the three known varieties (eukaryotic, bacterial, and archaeal flagella) represent an advanced protein-based structure that requires the interaction of its components within itself and with many systems; their molecular mechanism of motility and sensory transduction remaining elusive. An approach to the evolutionary origin of any cellular component(s) is to devise in silico homology searches among the protein or nucleotide sequences of the two components that one is trying to find evolutionary relatedness This very approach has suggested that a subset of the bacterial flagellar components is similar to the Type III secretory and transport system; the latter defensive systems provide the function of injecting a toxin into eukaryotic cells. If natural selection favored motility, at least for the sake of costbenefits, arrangement of the flagella seemed critical
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