Microbiology Terms Starting With F
Microbiology Glossary: F
Flagellum
/ fluh-JEL-um / · Latin flagellum (whip)
Flagellum is a long, helical, filamentous appendage extending from the bacterial cell surface that rotates, driven by a proton-motive force-powered motor, to propel the cell through liquid environments.
The bacterial flagellum consists of three main structural components: the basal body embedded in the cell membranes, the hook that connects the basal body to the filament and transmits rotational force, and the helical filament composed of polymerized flagellin protein subunits. Rotation of the motor can reach speeds of up to 100,000 rpm in some species, and switching the direction of rotation controls chemotaxis by alternating between smooth swimming runs toward attractants and tumbling that randomly reorients the cell. Flagellin is recognized by Toll-like receptor 5 on host immune cells, making the flagellum both a motility structure and a target of innate immunity.
Eukaryotic flagella, by contrast, bend through coordinated dynein motor activity along a 9+2 microtubule axoneme and are not homologous to the bacterial structure.
The flagellar motor of Vibrio alginolyticus can spin at over 100,000 rpm and switches rotational direction in under one millisecond, making it one of the fastest known biological rotary machines. This speed is powered entirely by sodium ions rather than protons, unlike the proton-driven motors of most other flagellated bacteria.
All bacteria have flagella. Many bacteria are nonmotile, and others move by entirely different mechanisms such as gliding, twitching via type IV pili, or gas vesicle-mediated buoyancy.
Salmonella enterica uses peritrichous flagella to swim through intestinal mucus during infection. Each flagellum rotates at roughly 10,000 rpm under physiological conditions, and a single cell may carry 6 to 10 flagellar filaments that bundle together during smooth swimming runs.
FtsZ
/ ef-tee-es-ZEE / · Scientific term used in bacterial cell biology.
FtsZ is a GTP-hydrolyzing bacterial protein that polymerizes into a contractile ring at the midcell and coordinates cell division by recruiting the machinery that synthesizes the new septum.
FtsZ polymerizes into the Z-ring at the future division site, with GTP hydrolysis driving the conformational changes that generate constrictive force. This ring recruits more than 20 additional proteins, including FtsA, FtsK, and penicillin-binding proteins, that collectively form the divisome and build the new cell wall septum. In Escherichia coli, midcell positioning of the Z-ring depends on two systems working together: nucleoid occlusion, which prevents ring assembly over the chromosome, and the Min system, whose proteins oscillate pole to pole roughly once per second to suppress off-center assembly.
As cytokinesis progresses, the ring’s diameter contracts from approximately 1 micrometer to less than 0.2 micrometers, physically pinching the cell into two daughters.
FtsZ shares structural and biochemical similarity with tubulin, the eukaryotic cytoskeletal protein, despite sharing less than 20 percent amino acid sequence identity. This relationship suggests that the ancestral cell division GTPase predates the divergence of bacteria and eukaryotes.
Bacteria divide without organized cell machinery. Proteins such as FtsZ precisely coordinate the division site, timing, and septum synthesis in a regulated sequence comparable in organization to eukaryotic cytokinesis.
Cell Cycle →Caulobacter crescentus, a freshwater bacterium used widely in cell biology research, assembles an FtsZ ring only at the stalked cell pole during its asymmetric division cycle. The ring constricts over roughly 20 minutes, after which the two daughter cells adopt distinct morphologies and fates.
Learn Cell Wall Concepts →