Bacteria

Kingdom Archaea Previously, we learned about the need for the taxa domain to help distinguish between the different types of bacteria. The domain Archaea was created to group organisms that did not quite fit into the kingdom bacteria due to their gene sequence, metabolism, and physical structure. It is believed that archaea are the oldest group of organisms on Earth. When evolutionists examine the genetic composition of archaea, they determined these prokaryotes resemble eukaryotic organisms more than bacteria. The phylogenetic tree would show that eukaryotes, like humans, and archaea have a common ancestor.

Archaea are prokaryotic unicellular organisms Archaea are prokaryotic unicellular organisms. They do not have a nucleus nor do they have membrane bound organelles. However, they do have a cell wall and a cell membrane that is structurally different from bacteria. In addition, archaea live in extreme environmental conditions. The structure of their cell membrane allows for their survival in extremely acidic conditions, saline environments and also in oxygen-free areas. The halobacteria shown here lives in an extremely salty environment.

Kingdom Eubacteria Bacteria are the most abundant and most diverse organisms on Earth. All bacteria are single-celled and prokaryotic (they do not have a nucleus). Their DNA consists of a single chromosome. Bacteria do not have any membrane bound organelles and they reproduce asexually by binary fission.

Bacteria are only 1-10 µm and therefore can only be seen with the help of a microscope. The bacteria Salmonella, which causes diarrhea, fever and abdominal cramps in humans, is shown. The image has been magnified 20863x using a colourized scanning electron micrograph (SEM).

Structure of Bacteria All bacteria have the same basic structure. The diagram below shows the cross-section of the bacterial cell. You will notice that some structures, cytoplasm, ribosomes are common to eukaryotic cells as well.

Virtual Microscope http://www.udel.edu/biology/ketcham/microscope/ Watch the instructional video to refresh how to use a microscope Then click on the virtual microscope link and examine a slide of a bacterial capsule

While the structure of bacterial cells is very similar, their shape is not. Bacterial cells are classified based upon their shape. There are three basic shapes: Rod-shaped Spiral-shaped Spherical-shaped

Rod-shaped Bacilli(pl.) Bacillus(sing.) Spiral-shaped Spirilla (pl.) Spirillum(sing.) Spherical-shaped Cocci (pl) Coccus(sing.)

Bacteria cells also have different types of arrangements. If they are clustered, like a bunch of grapes they are referred to as staphylo. If they are arranged in pairs they are called diplo and if they exist in long chains they are called strepto.

In the image on the left, you will notice fine dotted red lines. This is the bacteria streptococcus pyrogenes. It is arranged in long chains (strepto) and has a spherical shape (coccus).  Streptococcus pyrogenes is responsible for strep throat and scarlet fever. This image has been magnified 900x.

Practice – Match the following Staplococcus Spirillum Diplococci Diplobacillus Streptococcus Streptobacillus

Homework Name the type of Archaea that would survive in the following environmental conditions: Sewage sludge Dead Sea Hot sulphur springs Antarctic Human Intestines Archaea play an important role in biotechnology. What qualities make these organisms so useful? Describe the function of each component of the bacterial cell shown on slide six.