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