Characteristics
Applications
Species refers to organisms that have a distinct set of unique derived traits.
Different species will have different derived traits, these could be:
 physical appearance: e.g. fur thickness, snout length, body shape
 behavioural: e.g. prey preference, habitat choice, hunting strategy
 genetic composition: e.g. number of chromosomes, DNA sequence
Different species may mate but will produce sterile offspring
e.g. Female horse (64c) + male donkey (62c)  mule (63c)
The mule will not have any descendants because it is not fertile due to
differences in their chromosome number!
Prokaryotes
Eukaryotes
Prokaryote – single-celled organisms that lack a true nucleus
 Generally referred to as “microbes” or “bugs”
Two kingdoms of micro-organisms: Archaea and Eubacteria
 The overwhelming majority of the prokaryotes we deal with on a
daily basis are the Eubacteria.
Archaea bacteria:
 Usually are found in hostile environments:
e.g. hydrothermal vents, geysers,
oil wells, highly acidic/basic
or alkaline water.
Eubacteria:
 everywhere else including human body
1. All bacteria are single-celled
2. They are prokaryotes – their DNA is not compartmentalized
3. Cell organelles in bacteria are not surrounded by membranes
4. The DNA is made of a single chromosome
5. All bacteria reproduce asexually by binary fission
• Microbial Length Unit:
- Micrometer (µm) or ‘micron’
10-6meter (1 m = 1,000, 000 µm)
- Nanometer (nm)
10-9 meter (1 m = 1,000, 000, 000 nm)
• Bacterial cells range in size from 10 – 100 µm
 recent discoveries extend this size range to 500 – 1000 µm
“Typical” eukaryotic cell
“Typical” prokaryotic cell
Cell wall – provides structural support and protection for cell contents
Cell membrane – controls the passage of materials into and out of the cell
Cytoplasm – contains ribosomes, responsible for the formation of proteins,
and DNA, the genetic information of the cell
DNA – single stranded chromosome that forms a ring (Plasmid = double stranded)
Flagella/Cilia – some bacteria have them, stem from the cell wall and cell
membrane functioning as a propellers that help bacteria mobile
Bacteria are usually classified by:
shape, reaction to being stained,
nutrition, and respiration
(and not by phylogenetic relationships).
Coccus
 Plural: cocci
 spherical cell
Bacillus
 Plural: bacilli
 rod-like cell
Coccobacillus
 Plural: coccobacilli
 cells in between round & rod shape
Vibrio
 curved cell
Spirillum
 Plural: spirilla
 rigid, wave-like shaped cell
Spirochete
 corkscrew shaped cells
As a population: eg. Cocci
•
•
•
•
Monococci – live in separate cells
Diplococci – live in pairs
Streptococci – live in linear chains
Staphlococci – live in clusters
Bacteria are further grouped by their cell membrane composition.
To classify them, gram staining is used. The method works by checking how
the bacteria react to a dye made of crystal violet and iodine.
If it is Gram-positive bacteria:
- can retain the dye, hence purple
- very thick cell membrane
If it is Gram-negative bacteria:
- do not stain with Gram stain, hence appears
red/pinkish in color
- thinner cell membrane
- has a cell wall
- large periplasmic space
Bacteria are also classified based on how they obtain their energy and nutrients!
Autotrophs – make their own food
Photoautotrophs – similar to photosynthesis in plants, but no O2 is produced;
light = energy, organic and inorganic compounds used for nutrients
Chemoautotrophs – use inorganic substances to gain energy instead of
sunlight; inorganic chemicals = energy, organic and inorganic
compounds used for nutrients.
E.g. Cyanobacteria (found in hydrothermal vents)
Heterotrophs – consume food made by producers
Chemoheterotrophs – energy and nutrients from organic compounds
(humans are examples of this type of metabolism)
Photoheterotrophs – energy from sunlight and use organic compounds
for nutrients
There are specific terminology used to communicate bacteria with various
metabolism preference. Since oxygen is common, these terms are based on
bacterial: 1) needs for oxygen; 2) tolerance of oxygen; or 3) aversion to oxygen
Obligate aerobes – organisms that can only grow in the presence of O2
E.g. Bacteria that infect the respiratory system of humans; microorganisms that
live in the water column of lakes, rivers, and ocean
Facultative anaerobes – organisms that can grow in both in the presence and
the absence of O2.
E.g. Bacteria in the human intestines can be exposed to a range of conditions
from fully oxygenated (near the stomach) to completely without oxygen
(further into the intestines); an example of this type of organism is E. coli.
Obligate anaerobes – can only grow in environments where there is no O2
E.g. deep wounds on skin (hence the awful smell); deep in the soil and
sediments; in certain parts of sewage treatment plants
How to determine which respiration mode the
bacteria exhibit?
a) ?
b) ?
c) ?
Thioglycolate broth medium
(+ agar + resazurin)
How to determine which respiration mode the
bacteria exhibit?
a) Obligated Aerobes – oxygen can only
penetrate a short distance into the tube
b) Obligated Anaerobes – they are sensitive to
oxygen so grow away from the surface
c) Facultative Aerobes – are able to grow in
either the presence or the absence of
oxygen so grow throughout the tube
Thioglycolate broth medium
(+ agar + resazurin)
- Bacterial cells grow at an exponential rate when given the right type
and amounts of nutrients.
- Their mode of reproduction is asexual, by doubling themselves
This can translate into a doubling of the population every 20 minutes!
Step 1. Chromosomes duplicate
and copies get separated
Step 2. Cell elongates and copies
of chromosomes move
towards the poles
Step 3. Cell divides into two
daughter cells
N = No
n
2
N = Total final number of bacteria
No = Initial number of bacteria
n = number of generation
(1 generation = 20 minutes)
2  indicate binary fission
Example Problems:
1. To get ready for lunch, Hannah washes her hands very carefully after building a
sand castle. Assuming that her effort resulted in removing most bacteria off her
hands except for 36 bacteria. By the time she picks up the sandwich to eat 15
minutes later, how many bacteria are there on her hands at that time?
Given:
No = 36
n = 15 min
N = ?
15
 20
= 0.75
N = No2n
= 36 • (20.75)
= 36 • 1.68
= 61
Therefore, Hannah has 61 bacteria..
Binary Fission:
asexual process of reproduction
and therefore lacks exchange of
genetic material.
Transformation:
Bacteria picks up random DNA
fragment in the environment
(e.g. from other bacteria that
died) & incorporated into its
genome.
Conjugation:
the transfer of genes from one
cell to another and therefore
increases genetic diversity of a
population.
Step 1. F+ cell (donor) makes
contact with F- cell (recipient)
via their tubule pilus
Step 2. Conjugation tube form at site
of contact bridging the 2 cells
Step 3. Single-stranded DNA of the
plasmid gets transferred to the
recipient cell
Step 4. Conjugation tube disconnects.
Single-stranded DNA from each
cell duplicates making both F+ cells
Bacteria and Diseases:
-
Not all bacteria cause disease, but some do as part of their metabolism.
These few “bad” bugs give bacteria the group name of “germs”
Pathogen – disease causing agent
- Two general ways a pathogen can operate:
 Break down tissues for food (e.g. Tuberculosis)
 Release toxins that harm the host (e.g. Food poisoning)
- Many bacteria can be killed or kept in check with antibiotics or vaccines
 But problems arise when bacteria become resistant to our drugs.
How would this affect you?
Decomposers:
- Bacteria play a critical role in nature by recycling dead organisms
 Nutrients in dead organisms can be reused, instead of accumulating
 This requires the right mix of the following variables for maximum
decomposition to occur:
i) Temperature
ii) Gas availability for terminal electron accepting (O2 is the best)
iii) Water
- Widely used by humans to process dead materials
as detrivore to get rid of them or to recycle them.
e.g. bacteria eating Uranium
Fixing Nitrogen:
- Certain bacteria can convert useless nitrogen to useful nitrogen (fertilizer)
that can be used by other organisms
N2 gas (abundance but useless)
NH3 (ammonia) & other compounds
- This ability to transform nitrogen is called nitrogen fixation
- Nitrogen fixing bacteria are often found in root nodules of legumes (plants)
 these root nodules are functionally equal to fertilizer factory
 plants harbouring these fixing
bacteria grow relatively
faster and healthier.