Capsules help the organism adhere to host cells. The capsule also facilitates and maintains bacterial colonization of biological e. Last updated on June 21st, Bacterial spores are highly resistant, dormant structures i. When vegetative cells of certain bacteria such as Bacillus spp and […]. Last updated on June 18th, Lipopolysaccharide LPS layer also called the outer membrane is the outermost layer present only in the cell wall of gram-negative bacteria. Last updated on June 21st, Flagella singular, flagellum are the locomotory structures of many prokaryotes.
The flagellum functions by rotation to push or pull the cell through a liquid medium. Contents1 Bacterial Flagella 1. This site uses Akismet to reduce spam. Learn how your comment data is processed. News Ticker. Contents 1 Structure and Composition 2 Capsule Vs. Slime Layers 2. Bacterial Capsule. Anti-phagocytic nature of Bacterial capsule.
Structure of Bacterial Cells. About Acharya Tankeshwar Articles. Capsules also protect bacterial cells from engulfment by predatory protozoa or white blood cells phagocytes , or from attack by antimicrobial agents of plant or animal origin. Capsules in certain soil bacteria protect cells from perennial effects of drying or desiccation.
Capsular materials e. Colonies of Bacillus anthracis. The slimy or mucoid appearance of a bacterial colony is usually evidence of capsule production. In the case of B. The capsule is an essential determinant of virulence to the bacterium. In the early stages of colonization and infection the capsule protects the bacteria from assaults by the immune and phagocytic systems.
Some bacteria produce slime materials to adhere and float themselves as colonial masses in their environments. Other bacteria produce slime materials to attach themselves to a surface or substrate.
Bacteria may attach to surface, produce slime, divide and produce microcolonies within the slime layer, and construct a biofilm , which becomes an enriched and protected environment for themselves and other bacteria.
A classic example of biofilm construction in nature is the formation of dental plaque mediated by the oral bacterium, Streptococcus mutans. The bacteria adhere specifically to the pellicle of the tooth by means of a protein on the cell surface.
The bacteria grow and synthesize a dextran capsule which binds them to the enamel and forms a biofilm some cells in thickness. S-Layer Some bacteria have a highly organized layer made of secreted proteins or glycoproteins that self-assemble into a matrix on the outer part of the cell wall.
This regularly structured S-layer is anchored into the cell wall, although it is not considered to be officially part of the cell wall in bacteria. S-layers have very important roles for the bacteria that have them, particularly in the areas of growth and survival, and cell integrity. S layers help maintain overall rigidity of the cell wall and surface layers, as well as cell shape, which are important for reproduction. They can provide cell adhesion to other cells or surfaces.
For pathogenic bacteria they can provide protection from phagocytosis. The building blocks for these structures are typically made within the cell and then secreted past the cell membrane and cell wall, to be assembled on the outside of the cell. Fimbriae are thin filamentous appendages that extend from the cell, often in the tens or hundreds. They are composed of pilin proteins and are used by the cell to attach to surfaces.
They can be particularly important for pathogenic bacteria, which use them to attach to host tissues. Pili are very similar to fimbriae some textbooks use the terms interchangeably in that they are thin filamentous appendages that extend from the cell and are made of pilin proteins. Pili can be used for attachment as well, to both surfaces and host cells, such as the Neisseria gonorrhea cells that use their pili to grab onto sperm cells, for passage to the next human host.
So, why would some researchers bother differentiating between fimbriae and pili? Pili are typically longer than fimbriae, with only present on each cell, but that hardly seems enough to set the two structures apart.
It really boils down to the fact that a few specific pili participate in functions beyond attachment. The conjugative pili participate in the process known as conjugation , which allows for the transfer of a small piece of DNA from a donor cell to a recipient cell.
The type IV pili play a role in an unusual type of motility known as twitching motility , where a pilus attaches to a solid surface and then contracts, pulling the bacterium forward in a jerky motion. Bacterial motility is typically provided by structures known as flagella. The bacterial flagellum differs in composition, structure, and mechanics from the eukaryotic flagellum, which operates as a flexible whip-like tail utilizing microtubules that are powered by ATP. The bacterial flagellum is rigid in nature, operates more like the propeller on a boat, and is powered by energy from the proton motive force.
Berlin, Heidelberg: Springer Berlin Heidelberg; Mobile genetic elements associated with antimicrobial resistance. Clin Microbiol Rev.
American Society for Microbiology. Appl Environ Microbiol. Modular prophage interactions driven by capsule serotype select for capsule loss under phage predation.
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