# Gram Negative Bacteria --- **Gram negative bacteria** are type of [[bacteria]] with a thin [[peptidoglycan]] layer and an [[#outer membrane]]. In a lab they can be differentiated from a [[Gram positive bacteria]] by [[Gram stain|staining]] pink. ![[Gram negative stain.png]] ## Features Gram negative bacteria are so-called because they do not retain a particular lab dye very well. They are different from [[Gram positive bacteria]] bacteria because have a much *thinner* layer of [[peptidoglycan]] and a unique [[#outer membrane]] on top of the cell wall. The outer membrane of these bacteria protects them, and makes them generaly to treat than Gram positive bacteria. ![[Gram negative bacteria.png]] ### Outer Membrane The **outer membrane** of Gram negative bacteria is a unique structure that is found outside the [[peptidoglycan]] layer. It is a bilayer, but where most bilayers found in biology are two layers of [[phospholipid|phospholipids]], the outer membrane only has *one* layer of phospholipids (the inside layers) and the other layer is made up of [[#lipopolysaccharides]] (LPS). Also found in the outer membrane are lipoproteins and porins. #### Lipopolysaccharides **Lipopolysaccharides** are found in the [[#outer membrane]] of Gram negative bacteria, and help the cell transport magnesium made up of two parts, *Lipid A* and *O-polysaccharide*, or *O-[[antigen]]*. Because lipopolysaccharides can be deadly if they are released into the blood stream, they are also called "[[toxin#Endotoxin|endotoxins]]". ![[lipopolysaccharide.png]] #### Porins **Porins** are [[membrane transport protein|membrane transport proteins]] that are only found in the [[#outer membrane]] of Gram negative bacteria. They have a unique 3 part shape. #### Lipoproteins Bacterial **lipoproteins** are found in the [[#outer membrane]] of Gram negative bacteria and attach the outer membrane to the [[peptidoglycan]] layer. N.B.: This term is not to be confused with the lipid transporting vesicle [[lipoprotein|of the same name]], and sometimes referred to as "proteolipid" to avoid confusion. ### Periplasm or Periplasmic Space The **periplasmic space** is the area between the [[#outer membrane]] and the [[plasma membrane|cytoplasmic membrane]] of a Gram negative bacteria. ## Gram Negative in the Lab When staining in the [[labs]], Gram positive bacteria retain Gram's iodine very well, so it can be washed away very easily and then stained with Safranin, turning them pink. ___