A background in bacteria

Here are a few facts that we can start with.

Bacteria are simple, single-celled organisms. They have no organized organelles and genetic material is distributed throughout the inside of the cell.

A cell resembles a sealed bag, with the inside of the bag representing the inside of the cell (the cytoplasm), and the outside of the bag representing the rest of the world. separating these two worlds is one of the great unsung miracles of life, the cell membrane. This complex of molecules is far more than a simple covering and it is where interesting things happen both for the bacteria and for us in our story. We will begin with picking out the bacteria we are interested in and separating them from the rest.

Biological science is built upon classifying distinctions among organisms. One way scientists have grouped bacteria is by using a method called the Gram Stain. Hans Christian Gram was a scientist who discovered that if you put certain chemical pigments onto bacteria colonies, some would hold the dye and show up clearly under a microscope and others would not retain it. Those that hold the color are classified as Gram positive (G+) bacteria and those that do not are known as Gram negative (G-) bacteria. There are other groupings and types but these are the two we care about.

The difference in a G+ vs a G- bacteria has to do with the composition of the cell wall (membrane) that surrounds the bacteria and gives it some strength. Think of a balloon wrapped in plastic wrap. In bacteria, the strength of this wrapping comes from the materials that it is composed of and also how thick they are.

Gram positive bacteria have a thick cell wall made up or interlinked layers of a molecule called peptidoglycan. This thick wall forms

These Gram positive staphlyococcus illustrate the thick peptidoglycan wall that surrounds the cell of each individual bacterium. It is this wall that absorbs and holds the Gram stain.

a mesh in which the dye from the Gram stain gets trapped in the spaces of the mesh and is retained. It gives the bacteria a rigid shape and keeps it from drying out. Most terrestrial bacteria are Gram-positive. They need this thick wall to protect them from a sometimes hostile environment.

Gram negative bacteria have a different type of cell wall. It is thinner and less rigid. It contains a single layer of peptidoglycan for strength but most of the membrane is made of a molecule called lipopolysaccharide (LIP-OH-POLLY-SACK-A-RIDE). Gram-negative bacteria are more commonly found in aquatic environments where their environment helps support their more delicate forms. Here, a thick wall is not required for support and may actually hinder them from moving easily through the water. To us, water is fairly easily to navigate through but as things get smaller, water gets more viscous (thick). For a bacteria, moving through water is like a person trying to wade through liquid concrete.

Think of gram positive bacteria as a person wearing a thick wool sweater and a gram negative bacteria as a person in a nylon windbreaker and you will get the idea. The thick sweater is better for keeping out the cold while the windbreaker slips through the air better.

It is the molecule that makes up the cell wall of the gram negative bacteria, a molecular complex called lipopolysaccharide, or LPS, that is actually where we can begin our story. For it is here, way down at the smallest scale of matter, that little things happen that can affect our lives.

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