Bacterial cell structure
Typical examples include: Cell shape is generally characteristic of a given bacterial species, but can vary depending on growth conditions.
Some bacteria have complex life cycles involving the production of stalks and appendages (e.g. Caulobacter) and some produce elaborate structures bearing reproductive spores (e.g. Myxococcus, Streptomyces).
Therefore, a typical fully grown 1-liter culture of Escherichia coli (at an optical density of 1.0, corresponding to c. 109 cells/ml) yields about 1 g wet cell mass.
Peptidoglycan is made up of a polysaccharide backbone consisting of alternating N-Acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) residues in equal amounts.
The enzyme lysozyme, found in human tears, also digests the cell wall of bacteria and is the body's main defense against eye infections.
The cell wall of some Gram-positive bacteria can be completely dissolved by lysozymes which attack the bonds between N-acetylmuramic acid and N-acetylglucosamine.
In laboratory culture, the S-layer and capsule are often lost by reductive evolution (the loss of a trait in absence of positive selection).
The chemical structure of the outer membrane's lipopolysaccharide is often unique to specific bacterial sub-species and is responsible for many of the antigenic properties of these strains.
The chemical structure of the outer membrane lipopolysaccharides is often unique to specific bacterial strains, and is responsible for many of their antigenic properties.
The periplasm contains the peptidoglycan layer and many proteins responsible for substrate binding or hydrolysis and reception of extracellular signals.
The periplasm is thought to exist as a gel-like state rather than a liquid due to the high concentration of proteins and peptidoglycan found within it.
The relative proportions of these fatty acids can be modulated by the bacterium to maintain the optimum fluidity of the membrane (e.g. following temperature change).
The periplasm contains the peptidoglycan layer and many proteins responsible for substrate binding or hydrolysis and reception of extracellular signals.
The periplasm is thought to exist in a gel-like state rather than a liquid due to the high concentration of proteins and peptidoglycan found within it.
Fimbriae (sometimes called "attachment pili") are protein tubes that extend out from the outer membrane in many members of the Pseudomonadota.
They are generally short in length and present in high numbers about the entire bacterial cell surface.
Pili are similar in structure to fimbriae but are much longer and present on the bacterial cell in low numbers.
The exact function of S-layers is unknown, but it has been suggested that they act as a partial permeability barrier for large substrates.
Common forms include: The bacterial flagellum consists of three basic components: a whip-like filament, a motor complex, and a hook that connects them.
The processes concerning the transfer of genetic information — translation, transcription, and DNA replication — therefore all occur within the same compartment and can interact with other cytoplasmic structures, most notably ribosomes.
An early idea was that bacteria might contain membrane folds termed mesosomes, but these were later shown to be artifacts produced by the chemicals used to prepare the cells for electron microscopy.
Positive buoyancy is needed to keep the cells in the upper reaches of the water column, so that they can continue to perform photosynthesis.
Natural selection has fine tuned the structure of the gas vesicle to maximise its resistance to buckling, including an external strengthening protein, GvpC, rather like the green thread in a braided hosepipe.
Deep lakes that experience winter mixing expose the cells to the hydrostatic pressure generated by the full water column.
Bacterial microcompartments are widespread, organelle-like structures that are made of a protein shell that surrounds and encloses various enzymes.
provide a further level of organization; they are compartments within bacteria that are surrounded by polyhedral protein shells, rather than by lipid membranes.
Magnetosomes are bacterial microcompartments found in magnetotactic bacteria that allow them to sense and align themselves along a magnetic field (magnetotaxis).
It has been proposed that endospore formation has allowed for the survival of some bacteria for hundreds of millions of years (e.g. in salt crystals)[14][15] although these publications have been questioned.
Dipicolinic acid is a chemical compound which composes 5% to 15% of the dry weight of bacterial spores and is implicated in being responsible for the heat resistance of endospores.
Archaeologists have found viable endospores taken from the intestines of Egyptian mummies as well as from lake sediments in Northern Sweden estimated to be many thousands of years old.
