Download Monera/Bacteria

L.C. Biology
Revision
Kingdom Monera/Bacteria
Bacteria are prokaryotes from the kingdom Monera.
Distribution
Bacteria are found in fresh water, salt water, soil, dust, air, plants and animals. They can be found at temperatures higher than
100⁰C, ponds of high salt concentration, sewage, swamps and human intestines. They can survive extreme temperatures and
pressures and pH’s as low as 1 and 2.
Bacterial Structure
Cell wall
flagella
cytoplasm
plasmid
Strand of DNA
capsule
Function of parts of a bacterium
Capsule/Slime layer
Cell Wall
Flagellum
Cell membrane
DNA
Plasmid
Mesosome
Cell
membrane
Capsule is a dry layer, slime layer is moist – both help to
prevent water loss
Protects & prevents cell from expanding & bursting
Allows the cell to move/swim
Retains cell contents & controls what passes in & out of the
cell
The loop of DNA contains genes that control the cell
Small loop of DNA that contains genes that may control
antibiotic resistance
Respiration (how cell gets energy)
Size: bacteria are measured in micrometres (μm), most are 1-5 μm.
Types of bacteria: Bacteria are classified according to their shape.
1. Round/coccus. Example: Staphylococcus Aureus causes pneumonia.
2.
Rod/bacillus. Example: Bacillus Anthracis causes anthrax. Escherichia Coli
live in human gut.
3.
Spiral. Example: Treponema Pallidum causes syphillus.
Reproduction
Bacterial reproduction is asexual (one parent) and is called binary fission.
 Bacteria gets to a certain size & the DNA strand replicates
 Cell elongates and DNA strands move to opposite ends of cell
 Cell splits into two similar sized cells
L.C. Biology
Revision
Bacteria can divide every 20 minutes – one bacterium could give rise to over a million bacteria in 7 hours!!
Mutations in bacteria
Bacteria can evolve very fast due to the speed at which mutations can spread
throughout a population because of their short life cycles. This is how bacteria evolve
resistance to new antibiotics.
Endospores
 When growing conditions aren’t suitable the bacterial DNA replicates and a
tough wall forms around one of the DNA loops inside the parent cell.
 Parent cell breaks down and endospore remains dormant (not
growing/replicating).
 When conditions are suitable endospore absorbs water, the wall breaks and
cell reproduces by binary fission.
Nutrition
Bacteria can be autotrophic or heterotrophic.
1.
Autotrophic: means an organism makes its own food.
Autotrophic bacteria can be photosynthetic or chemosynthetic.
 Photosynthetic: bacteria that make food using sunlight e.g. purple sulphur bacteria.
 Chemosynthetic bacteria make food using energy from chemical reactions e.g. nitrifying bacteria in the nitrogen
cycle.
2.
Heterotrophic: means an organism takes in food made by other organisms.
Heterotrophic bacteria can be saprophytic or parasitic.
 Saprophytes are organisms that take in food from dead organic matter e.g. bacteria of decay
 Parasites are organisms that take in food from a live host usually causing harm e.g. bacillus anthracis
Factors affecting bacterial growth
Growth is affected by five factors, too much or too little of these is bad for bacteria. A limiting factor is something that slows
down a process when in short supply.
1.
Temperature: most bacteria grow best between 20 – 30⁰C, but some can tolerate higher temperatures. Low
temperatures can slow down the rate of bacterial growth.
2.
Oxygen concentration: Aerobic bacteria need oxygen for respiration (most bacteria are aerobic), a low oxygen
concentration can slow down bacterial growth. Anaerobic bacteria do not need oxygen for respiration.
Facultative anaerobes can respire with or without oxygen. Obligate anaerobes can only respire in the
absence of oxygen.
3.
pH: Bacterial enzymes work at specific pH values. Outside these values the bacterium’s enzymes will be
denatured.
 Most bacteria grow best at neutral pH, some can tolerate low pH’s. Heliobacter in the human stomach can
tolerate a pH of 2.
4.
External Solute Concentration: bacteria gain
or lose water by osmosis.
 If external solution has a higher solute (salt
or sugar) concentration than the bacteria’s
cytoplasm water will move out of the bacteria.
This dehydrates the bacteria and stops its
enzymes working. Used in food preservation.
 If external solution has a lower solute
concentration than the bacteria’s cytoplasm
water will move into the bacteria. Bacterial cell
walls usually prevent the bacteria from bursting.
L.C. Biology
Revision
5.
Pressure:
 Growth of most bacteria is inhibited by high pressures as their cell walls can’t withstand it.
 Bacteria found in deep sea vents can withstand high pressure. Pressure tolerant bacteria are sometimes formed
by genetic engineering as some biotechnology processes require the use of bacteria in pressurised bioreactors.
Economic Importance of Bacteria
Benefits:
 Lactobacillus convert milk to yoghurt/cheese
 Genetically modified bacteria can be used to make insulin, drugs, enzymes, alcohols
Disadvantages:
 Cause human, animal & plant diseases like tuberculosis, septic throat, food poisoning
Pathogens are micro-organisms that cause disease.
 Cause food to decay. Lactobacilli cause milk to go sour.
Antibiotics
Antibiotics are chemicals made by micro-organisms that stop the growth of or kill other micro-organisms without
damaging human tissue.
Antibiotics have no effect on viruses. Examples of antibiotics: streptomycin, penicillin.
Antibiotic Resistance
 Antibiotics kill most bacteria but some bacteria have developed antibiotic resistance by mutations, these aren’t affected
by the antibiotic, new antibiotics must be made continually to treat newly resistant bacteria.
 If a person is taking an antibiotics then all bacteria in that person are killed, if resistant bacteria evolve they’ve no
competition and will reproduce quickly and take over the persons body.
 If a pathogenic bacterium then enters the body the antibiotic-resistant gene may be passed on to it. The person will
develop an infection for which there is no antibiotic.
 In this way bacteria have developed that are resistant to most known antibiotics and are called multi-resistant bacteria.
Abuse of the use of antibiotics
 Overuse of antibiotics results in increased growth of antibiotic-resistant bacteria.
 If you don’t complete your course of antibiotics bacteria are allowed to survive and re-grow, this means more antibiotics
are needed and gives an increased risk of developing multi-resistant bacteria.
Growth Curve of Bacteria
Log Phase
Stationary
Phase
Decline
Phase
Death
Phase
Number of Bacteria
Lag phase
Time (days)
This diagram shows the growth curve of bacteria growing on a fixed amount of nutrient agar in a warm environment. The no. of
bacteria is in the log scale.
L.C. Biology
Revision
1. Lag phase:
Bacteria adapting to new environment and making enzymes to digest the substrate (agar), little if any increase in bacteria
numbers.
2. Log phase:
Bacteria reproducing rapidly due to ideal conditions of food, moisture, space, oxygen.
3. Stationary phase:
No increase in bacterial numbers, production of new bacteria is cancelled out by death of equal numbers of bacteria due to
lack of food, moisture, space, oxygen and the build up of toxic waste products.
4. Decline phase:
Death rate is higher than reproduction rate and bacterial numbers fall. High death rate due to factors outlined in no.3.
5. Death/survival phase:
Not all bacteria die, some survive as spores until conditions are suitable for growth.
Food Processing
Modern bioprocessing methods use bacteria to produce a range of products & food – yoghurts, cheese, vitamins, wine, beer.
A bioreactor is a vessel in which biological reactions take place.
The use of bacteria/fungi to produce edible forms of protein is called single-cell protein (SCP) production.
Two main methods of food processing: Batch culture & Continuous flow.
Both processes may/may not need oxygen bubbled through them & both need continuous rate of stirring.
1.
Batch Culture
 Fixed amount of sterile nutrient is added to micro-organism in bioreactor.
 Organisms go through lag, log, stationary phases of growth
 Product formed at log and stationary phases
 Process stopped before decline phase as this phase produces very little product & there’s a danger the microorganism would burst or produce unwanted side products.
 At the end bioreactor is emptied , product separated from solution & purified.
 Bioreactor is cleaned& sterilised, process started again.
Advantages:
 Simple process
 Small volumes of product can be formed
 Micro-organisms grow well (naturally)
2.
Continuous flow
 Nutrients continuously fed into bioreactor
 Culture medium continuously withdrawn (allows volume in bioreactor to remain constant)
 Micro-organisms maintained in log stage of growth – reproducing rapidly & making product at quick rate
 Micro-organisms grow under steady state – constant conditions of Ph, temperature, rate of stirring,
concentration of nutrients & oxygen.
 Difficult process to maintain constant conditions so limited to few applications like production of single-cell
protein.
Advantages:
 Production is continuous
 No need to sterilise bioreactor so often
 Product made more quickly
L.C. Biology
Revision
Bioreactor for Batch Food Processing
Nutrients and
microorganisms
added here
Gas out here
Stirrer
Product is
released at the
end of the process
Sparger
Oxygen (if required)
in here
Bioreactor for Continuous Flow Food
Processing
Nutrients fed in
continuously
Gas out here
Product (and
culture medium)
flows out
continuously
Stirrer
Sparger
Oxygen
in here
Product