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Bacteria
continued
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 grampositive 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 anthracis
Gram-positive
Escherichia coli
Gram-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.mcgrawhill.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/antibioticuse/antibiotic-resistance-faqs.html