Report on Gram Neg Bacteria

Gram-negative bacteria

Gram-negative bacteria are so called because they do not retain crystal violet dye, used in the Gram staining protocol. Gram staining is a method used to differentiate the two large groups of bacterial species into gram-positive and gram-negative groupings. Gram-positive bacteria do retain the crystal violet dye, which shoes up in their different cell wall structure. In a Gram stain test, a counterstain (commonly safranin) is added after the crystal violet, giving all gram-negative bacteria a red or pink colouring. Without the counterstain, the gram-negative bacteria would be colourless, which indicates that they have the much thinner cell wall associated with belonging to the gram-negative class. Thei8r thinner peptidoglycan cell wall layer does not retain crystal violet dye. Gram-positive bacteria have a thicker cell wall, which can retain the crystal violet dye when washed in a decolourizing solution. Compared with gram-positive bacteria, gram-negative bacteria are more resistant to antibiotics, despite their thinner peptidoglycan layer. This is seen to be due to their having an additional relatively impermeable lipid membrane known as a bacterial outer membrane.

The pathogenic capability of gram-negative bacteria is often associated with certain components of their membrane, in particular, the lipopolysaccharide layer (also known as the LPS or endotoxin layer). In humans, the presence of LPS triggers an innate immune response, activating the immune system and producing cytokines (hormonal regulators). Inflammation is a common reaction to cytokine production, which can also produce host toxicity. The innate immune response to LPS, however, is not synonymous with pathogenicity, or the ability to cause disease. In fact, the innate immune response is triggered purely by LPS.

The cytoplasm comprises cytosol – the gel-like substance enclosed within the cell membrane – and the organelles – the cell’s internal sub-structures. All of the contents of the cells of prokaryote organisms (such as bacteria, which lack a cell nucleus) are contained within the cytoplasm. Within the cells of eukaryote organisms the contents of the cell nucleus are separated from the cytoplasm, and are then called the nucleoplasm. The cytoplasm that most cellular activities occur, such as many metabolic pathways including glysolysis, and processes such as cell division. The inner, granular mass is called the endoplasm and the other, clear and glassy layer is called the cell cortex or the ectoplasm.

Movement of calcium ions in and out of the cytoplasm is thought to be a signalling activity for metabolic processes. In plants, movements of the cytoplasm around vacuoles are known as cytoplasmic streaming.

The cytoplasm has three major elements; the cytosol, organelles and inclusions.

Cytosol

The cytosol is the portion of the cytoplasm not contained within membrane-bound organelles. Cytosol makes up about 70% of the cell volume and is composed of water, salts and organic molecules.

The cytosol is a complex mixture of cytoskeleton filaments, dissolved molecules, and water that fills much of the volume of a cell. The cytosol also contains the protein filaments that make up the cytoskeleton, as well as soluble proteins and small structures such as ribosomes, proteasomes, and the mysterious vault complexes. The inner, granular and more fluid portion of the cytoplasm is referred to as endoplasm.

Proteins in different cellular compartments and structures tagged with green fluorescent protein. Due to this network of fibres and high concentrations of dissolved macromolecules, such as proteins, an effect called macromolecular crowding occurs and the cytosol does not act as an ideal solution. This crowding effect alters how the components of the cytosol interact with each other.

Organelles

Organelles (literally “little organs”), are usually membrane-bound, and are structures inside the cell that have specific functions. Some major organelles that are suspended in the cytosol are the mitochondria, the endoplasmic reticulum, the Golgi apparatus, vacuoles, lysosomes, and in plant cells chloroplasts.

Cytoplasmic Inclusion

The inclusions are small particles of insoluble substances suspended in the cytosol. A huge range of inclusions exist in different cell types, and range from crystals of calcium oxalate or silicon dioxide in plants, to granules of energy-storage material such as starch, glycogen, or polyhydroxybutyrate. A particularly widespread example are lipid droplets, which are spherical droplets composed of lipids and proteins that are used in both prokaryotes and eukaryotes as a way of storing lipids such as fatty acids and sterols. Lipid droplets make up much of the volume of adipocytes, which are specialised lipid-storage cells, but they are found in a range of other cell types.

nuronGram Neg Bacteria