Bacteria

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Gram Stain• When bacteria are treated with a dye made up of

crystal violet and iodine they react in one of two ways.

• Bacteria cells that appear purple are gram-positive and bacteria that change to pink are gram-negative.

• The colour difference is due to a variation in the cell wall of the bacteria.

• In general, gram-positive bacteria are more common and less pathogenic than gram-negative.

Below is an example of gram-positive bacteria, Bacillus anthracis and gram-negative bacteria, Escherichia coli.

Bacillus anthracisGram-positive

Escherichia coliGram-negative

Feeding Habits• Bacterial cells show variety in their nutritional

behaviours. There are two main types: autotrophs and heterotrophs.

• Autotrophs are capable of producing their own organic compounds (glucose) using carbon dioxide.

• Photoautotrophs use the energy from the sun and chemoautotrophs use the energy released from chemical reactions (oxidation/reduction) to synthesize their food.

• Most bacteria are heterotrophs. They obtain their nutrition by breaking down organic matter.

• Photoheterotrophs get energy from the sun while chemoheterotrophs use the energy released from chemical reactions.

Respiration• You may recall that the mitochondrion is the

“power-house” organelle of eukaryotic cells. • The organelle responsible for generating ATP in

eukaryotic cells does not exist in bacterial cells. • However, bacterial cells have the capability to

carry out cellular respiration and the method they use to produce ATP provides another classification.

• Bacteria that break down their food in the presence of oxygen are termed aerobes.

• Obligate aerobes must have oxygen available to survive.

• Anaerobes can respire in the absence of oxygen.

• Obligate anaerobes will die in the presence of oxygen.

• Facultative anaerobes display the flexibility to respire in the presence or absence of oxygen.

Reproduction• Most bacteria reproduce asexually by binary

fission. • Binary fission as you may recall resembles

mitosis. • That is, at the end of the process, two

identical cells are formed that have the exact same genetic information as shown.

• When conditions are not favourable, bacteria cells have the capability to reproduce sexually.

• However, this process only works in one direction.

• One cell donates the genetic information and the other receives it.

• Through the process of conjugation, a bacterial cell transfers genetic information called a plasmid.

• A plasmid is a portion of DNA that does not originate from the bacterial genome and contains only a few genes.

Conjugation animation

• http://highered.mcgraw-hill.com/olc/dl/120082/bio_f.swf

• Plasmids allow bacterial cells to produce additional genes that allow them to adapt to changing environmental conditions like temperature or the presence of antibiotics.

• Antibiotic-resistant bacteria began to evolve during the 1950s when doctors noticed that specific antibiotics were no longer working on certain bacteria.

• Antibiotic resistance occurs when the infecting bacteria cells are not completely killed off.

• If a small population of the bacteria cells survive the treatment and are able to reproduce, new bacteria cells equipped with resistance are born.

• As shown in the diagram, the yellow bacteria cells are destroyed by the antibiotic.

• However, the red bacteria cells are not affected by the antibiotic and are able to produce more antibiotic resistant bacteria.

• The evolution of antibiotic resistance can be linked to the following causes:

1. Failure to take the entire prescribed course of the antibiotic.

2. Inappropriate antibiotic treatment.3. Antibiotics used in agriculture to

prevent sickness and disease in animals enter the food supply.• More costly antibiotics are needed to treat

antibiotic resistant bacteria.

Helpful Bacteria• You may think that all bacteria are harmful;

however, most bacteria are beneficial. • Yogurt, cheese, and anything labelled “probiotic”

all contain bacterial cultures. • The bacteria in your gut help you digest your

food. • Nitrogen-fixing bacteria found in the soil or in the

roots of plants help to remove nitrogen from the air and convert nitrogen to the nitrates that plants use to construct proteins.

• We rely heavily on the use of bacteria to help decompose waste materials.

• Dead organisms and the waste from organisms provide nourishment to bacteria, which consume the matter as their source of energy for growth and reproduction.

• In addition, bacteria are used to decompose toxic materials, clean up oil spills and break down sewage.

Homework• Classify each of the following bacteria by their

nutritional pattern.– rhodospirillum– cyanobacteria– Nitrobacter hamburgensis– Mycobacterium tuberculosis

• In addition to their nutritional pattern, provide two more pieces of information for each bacterium listed above.

• Read this FAQ page about antibiotics:• http://www.cdc.gov/getsmart/antibiotic-use/anti

biotic-resistance-faqs.html