Bacteria Notes

Revision 4
© 2007-2015 by Zack Smith. All rights reserved.


Bacteria overview

E Coli

Bacteria are prokaryotes, so they lack a nucleus or organelles.

Sizes from 0.3 to 15 micrometers.

The world is full of bacteria. They are all over us, inside us, they help us with metabolism, and they protect people from bad organisms.

More O2 is produced by bacteria when by plants.

Some antibiotics can kill off good bacteria that guard against yeast infections. When you are on antibiotics, you should eat yogurt to replace good bacteria.

Bacteria parts


  • Nucleoid = central circle of DNA (1 chromosome

  • Inclusions = vacuoles, e.g. metachromatic inclusion which stores phosphorous

  • Plasmids = extrachromosomal DNA; these can provide resistance to antibiotics.

  • Cell membrane = phosphlipid bilayer with built-in ATP synthase and ETC (electron transport chain)

  • Cell wall = rigid layer of peptidoglycan (polypeptides & sugar chains) that keeps the shape of the bacterium even in situations where there is too much or too little water (hypotonic, hypertonic).

  • Ribosomes

  • Capsule (optional), also known as slime layer, which has the purpose sticking the bacteria to some spot where food is hopefully plentiful e.g. teeth. It also hides the bacterium from the immune system. Made of glycocalyx.

  • Pili (singular pilus): protrusions that help the bacterium hang on to other objects and which also allow bacteria to send genetic material to one another (F+ dominant to F- recipient). This gene transfer is like a simple early sexual system.

  • Lipopolysaccharide or LPS layer (optional): this chemical is a neurotoxin for animals.

  • Cytoplasm.

  • Flagella (optional)


There are three shapes:

  • Coccus = spherical, e.g. streptococcus
  • Bacillus = rod shaped, e.g. lactobacillus
  • Spirillium = spiral


Movement is via flagella. Bacteria have several flagella configuations.

  • Monotrichous = one flagellum
  • Lophotrichous = many flagella at one end
  • Amphitrichous = one flagellum at each end
  • Peritrichous = many flagella all over
  • Atrichous = no flagella

Swimming with flagella in pursuit of a chemical marker is chemotaxis.

Energy food consumption

There are four ways of getting energy:

  • phototrophic = it makes its own energy using light to catalyze chemical reactions
  • chemotrophs = they consume chemical matter e.g. other organisms
  • aerobes = they consume oxygen
  • anaerobes = they are killed by O2


Penicillin prevents bacteria from forming the peptidoglycan cell wall. Resistance to penicillin is caused by a bacterium developing an enzyme to break it down.

  • Tears have an enzyme lysozyme that breaks down peptidoglycan. The bacteria that cause pink eye have an enzyme that breaks down lysozyme.
  • Resistance to antibiotics is transferred between bacteria due to plasmid transfer along a pilus.
  • Some antibiotics target bacterial ribosomes, which are very different from non-bacterial ribosomes. Examples: erythromycin, tetracycline.

Capsule slime layer

The sticky layer lets bacteria stick to useful sites e.g. to teeth, to rocks, to bronchioles (bronchitis).

Bacteria which lack the capsule are easily killed by the immune system.


They reproduce by binary fission, which is like mitosis.


In adverse environments, some bacteria form a wall around the nucleoid that protects them long-term, even for millions of years.

Anthrax has survived for millions of years in its endospore form.

Endosymbiotic theory

This theory says that eukaryotes got their mitochondria & chloroplasts by ingesting bacteria but for some reason not eaten. It is supported by at least the following evidence.

  • Mitochondria and chloroplasts are the same size as bacteria.
  • Mitochondria and chloroplasts produce energy in a very similar way to bacteria.
  • Mitochondria and chloroplasts have their own DNA, which are a single circular chromosome.
  • Mitochondria and chloroplasts DNA has been scanned and are very similar to the DNA of bacteria.
  • Eukaryotes are known to ingest bacteria.

Nitrogen fixation

Some bacteria convert N2 to ammonia NH3. This is useful to plants.


Only 1% of bacteria are harmful. The rest are helpful to various extents.

The Gram test (invented by Hans Gram) is supposed to test for toxicity by detecting LPS. Gram positive means nontoxic, Gram negative means toxic. However there are many exceptions.


There are 3 symbiotic modes:

  • Mutualism, in which both bacteria & host benefit.
  • Commensalism, in which bacteria benefit and host is neither harmed nor helped.
  • Parasitism, in which bacteria benefit but the host is harmed.

Well known bacteria

  • E. Coli
  • Clostridium botulidium
  • Streptococcus
  • Staphococcus
  • Congentoritis = causes pink eye
  • Borrelea burgdorferi = Lyme disease (left untreated it attacks the joints, then the brain
  • Lactobacillus = used to make yogurt
  • Heliobacter pylori = causes ulcers
  • Trychonympha = bacteria that termites rely upon to break down wood.