Periplasmic Space: This cellular compartment is unique to bacteria that possess both an outer and plasma membrane (e.g. Gram negative bacteria). Enzymes and other proteins are found in the area, which aid in digestion and the movement of nutrients into the cell. Cell Wall: Made up of peptidoglycan (polysaccharides + protein), the cell wall helps the bacterial cell retain its overall shape. Coccus (spherical), bacillus (rod-shaped), and spirillum are the three basic forms of bacteria (spiral). Mycoplasma are bacteria without a cell wall, and hence lack a distinct form. Outer Membrane: This lipid bilayer is present in Gram negative bacteria and is where lipopolysaccharide (LPS) is located. This layer is absent in Gram positive bacteria. LPS has the potential to be hazardous to the host and to activate the immune system of the host. Capsule: This coating of polysaccharides (and sometimes proteins) shields the bacterial cell and is often linked with harmful bacteria because it acts as a barrier to white blood cell phagocytosis. Capsules may be visible when bacteria are seen in India ink.
A robust PG mesh is required to preserve cell shape and to protect the cell wall from stress caused by external stimuli. Simultaneously, bacterial cell development and separation necessitate a high degree of PG flexibility. These two contradictory requirements need the coordinated and balanced activity of PG synthesizing and degrading enzymes. When this balance is disrupted, growth halt and cell lysis may occur. In bacteria, this balance is maintained primarily by the regulation of potentially fatal autolytic enzymes, or PGHs. PGH regulation may occur at the transcriptional level or by post-transcriptional changes of PGHs or their substrate, PG [60, 61, 80]. Controlling the action of PGH
Flagella - Flagella (singular, flagellum) are hairlike structures that enable bacteria to move. They may be present on one or both ends of a bacterium, as well as across the whole surface of the bacterium. The flagella beat in a propeller-like pattern to assist the bacterium in moving toward nutrients, away from hazardous substances, or toward the light in the case of photosynthetic cyanobacteria. The nucleoid is an area of cytoplasm that contains the chromosomal DNA. It is not a membrane-bound nucleus, but rather a region of the cytoplasm containing DNA strands. While the majority of bacteria have a single circular chromosome responsible for replication, a few species have two or more. The cytoplasm also contains smaller circular auxiliary DNA strands called plasmids.
As in eukaryotes, bacterial DNA is not bundled utilizing histones to create chromatin but rather exists as a very compact supercoiled structure whose exact composition remains unknown.
[6] Although the majority of bacterial chromosomes are circular, there are occasional occurrences with linear DNA (e.g. Borrelia burgdorferi). Typically, a single bacterial chromosome is present, however certain species have been documented with several chromosomes. [5] Along with chromosomal DNA, most bacteria have tiny autonomous bits of DNA called plasmids. These plasmids often encode for features that are favorable but not required for the bacterial host. Plasmids are readily acquired or lost by bacteria and may be transported horizontally across bacteria. Thus, plasmids may be thought of as an addition to the chromosomal DNA of a bacterial cell.
