CharacteristicsApplications

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 offspringe.g. Female horse (64c) + male donkey (62c) mule (63c)

The mule will not have any descendants because it is not fertile due todifferences 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/basicor 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” prokaryotic cell

“Typical” eukaryotic 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 cellmembrane 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 cellBacillus Plural: bacilli rod-like cellCoccobacillus Plural: coccobacilli cells in between round & rod shapeVibrio curved cell

Spirillum Plural: spirilla rigid, wave-like shaped cellSpirochete corkscrew shaped cells

As a population: eg. Cocci

••••

Monococci – live in separate cellsDiplococci – live in pairsStreptococci – live in linear chainsStaphlococci – live in clusters

Bacteria are further grouped by their cell membrane composition.To classify them, gram staining is used. The method works by checking howthe 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 foodPhotoautotrophs – 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 ofsunlight; inorganic chemicals = energy, organic and inorganiccompounds used for nutrients.E.g. Cyanobacteria (found in hydrothermal vents)

Heterotrophs – consume food made by producersChemoheterotrophs – 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 variousmetabolism preference. Since oxygen is common, these terms are based onbacterial: 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 thatlive in the water column of lakes, rivers, and ocean

Facultative anaerobes – organisms that can grow in both in the presence andthe absence of O2.

E.g. Bacteria in the human intestines can be exposed to a range of conditionsfrom 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 andsediments; in certain parts of sewage treatment plants

How to determine which respiration mode thebacteria exhibit?

a) ?

b) ?

c) ?

Thioglycolate broth medium(+ agar + resazurin)

How to determine which respiration mode thebacteria exhibit?

a) Obligated Aerobes – oxygen can onlypenetrate a short distance into the tube

b) Obligated Anaerobes – they are sensitive tooxygen so grow away from the surface

c) Facultative Aerobes – are able to grow ineither the presence or the absence ofoxygen so grow throughout the tube

Thioglycolate broth medium(+ agar + resazurin)

- Bacterial cells grow at an exponential rate when given the right typeand 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 duplicateand copies get separated

Step 2. Cell elongates and copiesof chromosomes movetowards the poles

Step 3. Cell divides into twodaughter cells

n = 15 min 20 = 0.75

N = No2nN = Total final number of bacteriaNo = Initial number of bacterian = 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 asand castle. Assuming that her effort resulted in removing most bacteria off herhands except for 36 bacteria. By the time she picks up the sandwich to eat 15minutes later, how many bacteria are there on her hands at that time?

N ====No2n

36 • (20.75)36 • 1.6861

15Given:

No = 36

N = ? Therefore, Hannah has 61 bacteria..

Binary Fission:asexual process of reproductionand therefore lacks exchange ofgenetic material.

Conjugation:the transfer of genes from onecell to another and thereforeincreases genetic diversity of apopulation.

Transformation:Bacteria picks up random DNAfragment in the environment(e.g. from other bacteria thatdied) & incorporated into itsgenome.

Step 1. F+ cell (donor) makescontact with F- cell (recipient)via their tubule pilus

Step 2. Conjugation tube form at siteof contact bridging the 2 cells

Step 3. Single-stranded DNA of theplasmid gets transferred to therecipient cell

Step 4. Conjugation tube disconnects.Single-stranded DNA from eachcell 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 materialsas 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 relativelyfaster and healthier.