chapter 20: kingdom monera bacteria are ubiquitous – they are found everywhere fresh water, sea...
TRANSCRIPT
Chapter 20: Kingdom MoneraChapter 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
Basic Structure of BacteriumBasic Structure of Bacterium
DNA (nucleoid)Cell Wall
Cell membrane
Plasmid
Capsule
CytoplasmFlagellum
(Note: rod-shaped bacterium)
Types of BacteriumTypes of Bacterium
1. Rods
2. Round
3. Spirals
Bacterial ReproductionBacterial 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
Binary FissionBinary Fission
DNA and plasmid replicated
Bacterium elongates and DNA and plasmid move to opposite ends of cell
Bacterial cell splits in two
Bacterial NutritionBacterial 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
Bacterial NutritionBacterial 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
Parasitic BacteriaParasitic 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
Factors Affecting GrowthFactors Affecting Growth
1. Temperature (lower temperature slow down enzyme action and hence bacterial growth)
2. Oxygen (although some bacteria do not use oxygen)3. pH (enzymes are affected by pH and thus pH affects
bacterial growth and metabolism)4. Solute concentration (osmosis affects bacterial
metabolism)5. Pressure (air pressure affects bacteria due to the cell
wall not being strong enough to withstand high pressures)
6. Water (although some bacteria do not use water, others resort to endospore formation when there is not enough moisture)
Endospore FormationEndospore 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
Endospore FormationEndospore FormationUnfavourable conditions: DNA and plasmid replicated
Endospore is released following bacterial death
Endospore is formed around replicated DNA
Favourable conditions
Economic Importance of Economic Importance of BacteriaBacteria
• 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
AntibioticsAntibiotics• 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)
Bacterial Growth CurveBacterial Growth CurveN
um
ber
s o
f b
acte
ria
Time (days)
LAG
LOG
STATIONARY
DEATH
SURVIVAL
Bacterial Growth CurveBacterial 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
BioprocessingBioprocessing
• 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:1. Batch Culture
2. Continuous Flow Culture
1. Batch Culture1. Batch Culturei. In batch culture, a fixed amount of food (batch of food)
is added to bioreactorii. 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
iii. Most of the product is formed in the log and stationary phases (therefore reaction is normally stopped before the death phase)
iv. At the end of the reaction the product is removed and the bioreactor is cleaned out ready for another ‘run’
v. 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
2. Continuous Flow Culture2. Continuous Flow Culturei. Nutrients are continuously infused into the
bioreactor of continuous flow cultures and media removed is removed with product
ii. In this way the bacteria are kept in the log phase of growth
iii. pH, temperature, oxygen concentration, nutrient concentration and waste build-up are tightly controlled to maintain optimal conditions
iv. Advantage of continuous flow culture is that product is continually produced
v. Disadvantage of continuous flow culture is that conditions have to maintained within narrow limits and this is very difficult and expensive