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

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

Types of Bacterium Rods Round Spirals

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

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

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

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

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

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)

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

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

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

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)

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

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

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

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

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