1. Chapter 20: Kingdom Monera
Bacteria are ubiquitous – they are found everywhere
Fresh water, sea water, air-borne, and soil bacteria
Bacteria are prokaryotic in nature – i.e. they have no membrane-bound nucleus or organelles – the area occupied by the DNA in bacteria is called the nucleoid

2. Basic Structure of Bacterium
Cell membrane
Cytoplasm
Flagellum
Capsule
DNA (nucleoid)
Cell Wall
Plasmid
(Note: rod-shaped bacterium)

3. Types of Bacterium
Rods
Round
Spirals

4. Bacterial Reproduction
Bacteria reproduce by a process called binary fission – it is a type of asexual reproduction
Bacterium replicates its DNA and plasmid
The two pieces of DNA and plasmids move to opposite ends of the cell
The bacterium splits in two
In ideal conditions bacteria are capable of reproducing every 20 minutes

5. Binary Fission DNA and plasmid replicated
Bacterium elongates and DNA and plasmid move to opposite ends of cell
Bacterial cell splits in two

6. Bacterial Nutrition Autotrophic (bacterium makes its own food):
Photosynthetic bacteria contain chlorophyll and use sunlight energy to make food – e.g. purple sulphur bacteria
Chemosynthetic bacteria use ammonia, sulphur and iron compounds to make food – e.g. nitrifying bacteria

7. Bacterial Nutrition
Heterotrophic (bacterium obtains food made by other organisms):
Saprophytic bacteria take in food from dead organic matter – e.g. decomposer bacteria in soil
Parasitic bacteria take in food from a live host – e.g. disease-causing (pathogenic) bacteria

8. Parasitic Bacteria
Parasitic bacteria are usually disease-causing (pathogenic) bacteria:
Helicobacter pylori:
Stomach ulcers
Clostridium botulinum:
Botulism
Streptococcus pneumoniae:
Pneumonia
Bacterial meningitis
Treponema pallidum:
Syphilis
Streptococcus pyogenes:
Strep throat
Tonsilitis
Scarlet fever

9. Factors Affecting Growth
Temperature (lower temperature slow down enzyme action and hence bacterial growth)
Oxygen (although some bacteria do not use oxygen)
pH (enzymes are affected by pH and thus pH affects bacterial growth and metabolism)
Solute concentration (osmosis affects bacterial metabolism)
Pressure (air pressure affects bacteria due to the cell wall not being strong enough to withstand high pressures)
Water (although some bacteria do not use water, others resort to endospore formation when there is not enough moisture)

10. Endospore Formation
Under unfavourable conditions bacteria are still able to survive – they do this by forming endospores that protect the bacterial cells from harsh conditions
Endospore formation:
The bacterial DNA is replicated and is then enclosed within a tough protein-carbohydrate coat complex
When the bacterial cell dies the endospore is released and can survive a very long time
The endospore absorb water when conditions become favourable again and the bacterium reproduces again by binary fission

11. Endospore Formation
Unfavourable conditions: DNA and plasmid replicated
Favourable conditions
Endospore is released following bacterial death
Endospore is formed around replicated DNA

12. Economic Importance of Bacteria
Two beneficial effects of bacteria:
Lactobacillus is used to produce yoghurt and cheese
Escherichia coli has been genetically modified (by introduction of human genes) to produce human insulin and growth factor as well as enzymes, certain amino acids, and vitamins
Two harmful effects of bacteria:
Bacteria cause human disease (pathogenic)
Bacteria cause food to spoil

13. Antibiotics
Antibiotics are chemicals produced by microorganisms that are able to prevent growth of, or kill, other microorganisms without damaging animal tissues
Antibiotics are used to control bacterial infections in humans and animals
Antibiotics have been overused by some, thereby increasing antibiotic resistance among certain strains of bacteria (there are a handful of bacterial strains that now have complete resistance to all known antibiotics and this could create a human pandemic in the future)

14. Bacterial Growth Curve
STATIONARY
Numbers of bacteria
LOG
DEATH
LAG
SURVIVAL
Time (days)

15. Bacterial Growth Curve
There are 5 phases of bacterial growth:
Lag: bacteria are adapting to environment – no increase in bacterial numbers
Log: bacteria have ideal conditions and are reproducing at their maximal rate
Stationary: conditions become limiting – such as food/space and bacterial reproduction = bacterial death
Decline/Death: continued lack of food and space and build-up of toxins causes the death rate to increase above the reproduction rate and the numbers fall
Survival: a small number of bacteria survive as endospores and remain dormant until conditions become favourable again

16. Bioprocessing
As well as enzymes, bacteria can be used in bioprocessing to produce useful products including yoghurts, cheeses antibiotics, human proteins etc.
There are two methods by which bacteria are used in bioprocessing:
Batch Culture
Continuous Flow Culture

17. 1. Batch Culture
In batch culture, a fixed amount of food (batch of food) is added to bioreactor
The bacteria go through the lag, log and stationary phases of growth before the reaction is stopped and a certain amount of product is formed
Most of the product is formed in the log and stationary phases (therefore reaction is normally stopped before the death phase)
At the end of the reaction the product is removed and the bioreactor is cleaned out ready for another ‘run’
Advantages of batch culture are that it is easy to control, it can be run only when needed, and the bacteria go through a normal life cycle and so waste products don’t build up to high levels

18. 2. Continuous Flow Culture
Nutrients are continuously infused into the bioreactor of continuous flow cultures and media removed is removed with product
In this way the bacteria are kept in the log phase of growth
pH, temperature, oxygen concentration, nutrient concentration and waste build-up are tightly controlled to maintain optimal conditions
Advantage of continuous flow culture is that product is continually produced
Disadvantage of continuous flow culture is that conditions have to maintained within narrow limits and this is very difficult and expensive