A flagellum is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Bacterial flagella are helical filaments, each with a rotary motor at its base which can turn clockwise or counterclockwise.
The helical flagellum is supposed either to rotate as a whole, like a rigid corkscrew or to deform continuously in a traveling helical wave, like a helical snake. The two motions are externally indistinguishable in the limit of vanishing thickness of the helical filament, but the latter case calls for some mechanism inside the flagellum to drive the wave.
Bacteria mainly comprises a simple cellular structure, including:
- Capsule
- Cell wall
- Flagellum
- Pili
- Cytoplasm
- Ribosomes
- Chromosomes.
Bacteria are a giant group of minute, unicellular living organisms, which are also called microbes or microorganisms. These microscopic organisms are called prokaryotes as they lack a true nucleus and other cellular organelles.
Other structural features of these prokaryotic microorganisms are:
- It lacks a membrane-bound nucleus.
- It has a circular-shaped, single chromosome of DNA found within the cytoplasm.
- The nucleoid of a bacterial cell comprises the chromosome with its associated proteins.
- Every bacterial cell has its own plasmids, which are involved in some functions like antibiotic resistance.
- These plasmids are small, circular, extrachromosomal double-stranded DNA structures, which are naturally found in all bacterial cells. Plasmids are used as cloning vectors in rDNA technology.
- The mode of reproduction process in bacteria is both through sexual and asexual methods. Most bacteria rely on binary fission.
Most of the studies on bacteria‐driven microswimmers adopt a similar design, which is a sphere‐shaped microbead driven by single or multiple flagellated bacteria attached to it in random locations and orientations. Scanning electron microscope (SEM) images show that bacteria typically attach to spherical surfaces on their sides or with a small tilt angle, but other than that, the attachment orientation of bacteria is purely random.
Below is a summary of the major assumptions of the bacterial multicellular propulsion model:
- Attached bacteria maintain their positions and orientations over time and perform rigid body translation and rotation together with the sphere;
- Attached bacteria transition between run and tumble states and exert different forces and torques under different states;
- Interactions between the attached bacteria on the same sphere, if exist, are small and thus negligible for studying the behavior of the microswimmers;
- Interactions between bacterial flagella and the sphere surface are negligible;
- The swimming motion occurs at low Reynolds numbers and can be approximated by Stokes’ flow around a sphere, where the fluid drag due to attached bacteria is neglected;
- Physical interactions among the microswimmers are neglected due to their low concentration in the medium.
Bacterium E. coli[1] develops many flagella which are long, thin, helical filaments attached to rotary motors. When rotated in unison they enable the cell to swim by propulsion.
Footnotes
- Escherichia coli ( also known as E. coli) is a Gram-negative, facultatively anaerobic, rod-shaped, coliform bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms. Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in their hosts and are occasionally responsible for food contamination incidents that prompt product recalls. Most strains do not cause disease in humans and are part of the normal microbiota of the gut; such strains are harmless or even beneficial to humans (although these strains tend to be less studied than the pathogenic ones). [Back]
Further Reading
Sources
National Library of Medicine
Wikipedia
Proceedings of the National Association of Sciences
Science Advantages
Science Daily
BYJU’s
