www.mrcbiology.com 3.1.3 Monera – Bacteria Bacteria Bacterial Nutrition • Bacteria belong to the kingdom Monera. They are Bacterial reproduction unicellular organisms • Bacteria reproduce asexually Autotrophic and Heterotrophic • Also known as prokaryotes as they have no • The method used is called Binary Fission Autotrophic – organisms which make their own food membrane bound nucleus or membrane bound cell Heterotrophic – organisms which take in food made by organelles other organisms • They are classified according to three shapes Binary Fission o Spherical (cocci) • The chromosome attaches to the o Rod (bacillus) plasma membrane and the DNA Autotrophic Bacteria o Spiral (spirillum) is replicated • The cell elongates and the two Bacterial Shapes chromosomes separate Autotrophic • The cell wall grows to divide the (make food) Spherical (cocci) cell in two E.g. Staphlococcus aureus • Two identical daughter cells are causes pneumonia formed Rod (bacillus) E.g. Bacillus anthracis causes anthrax Bacterial Reproduction Photosynthetic Chemosynthetic Escherichia coli (E.coli) live in human gut • Bacteria reproduce asexually - their offspring are e.g. e.g. genetically identical Purple sulphur Nitrifying Spirillum (spiral) • As there is little recombination of genetic material in bacteria bacteria E.g.Treponema pallidum causes syphilis this method of reproduction one would expect that bacteria would be slow to evolve Bacterial Structure • Bacteria has a very short lifecycle (some can reproduce every 20 minutes). Heterotrophic Bacteria • New mutations can spread very quickly • This is how bacteria evolve resistance to new antibiotics Heterotrophic (Take in food) Endospore formation • Some bacteria can withstand unfavourable Cell Parts & Function conditions by producing endospores • Formed when the bacterial chromosome replicates Cell wall - shape & structure • One of the new strands becomes enclosed in a Cytoplasm - contains ribosomes and storage granules tough-walled capsule called an endospore Saprophytic Parasitic but no mitochondria or chloroplasts • Parent cell breaks down - endospore remains e.g. e.g. Nuclear material - single chromosome of DNA dormant Bacteria of decay Streptococci Capsule* - protection • When conditions are favourable the spores absorb Flagella* - movement water, break their walls and reproduce by binary Plasmid* - circular piece of DNA containing few genes fission for drug resistance * Sometimes present. www.mrcbiology.com 3.1.3 Monera – Bacteria Factors affecting the growth of 4. External Solute concentration bacteria • Bacteria can gain or lose water by osmosis Antibiotics • If the external solute concentration is • For the maximum growth rate bacteria must have o higher than the bacterial cytoplasm water will • Antibiotics are substances access to a food source and the conditions of their move out of the bacteria (Dehydration) produced by micro-organisms environment must be monitored closely o Food preservation techniques are based on this that stop the growth of, or kill, • Too much or too little of any of the following factors • Bacteria can gain or lose water by osmosis other micro-organisms without will slow down the growth of bacteria: • If the external solute concentration is damaging human tissue. 1. Temperature o lower than the bacterial cytoplasm solute • Antibiotics can be used to control bacterial and 2. pH concentration water will enter the bacteria fungal infections but do not effect viruses 3. Oxygen concentration o Cell wall will prevent bursting in most cases • The first antibiotic, Penicillin, was isolated from a 4. External solute concentration fungus was by Sir Alexander Fleming 5. Pressure 5. Pressure • Now antibiotics are mostly produced by genetically engineered bacteria 1. Temperature • The growth of most bacteria is inhibited by high • When an antibiotic is used to treat an infection most pressures. of the bacteria are killed • Most bacteria grow well between 20°C and 30°C. • Some bacteria can withstand high pressures. • Mutations in bacterial genes can allow bacteria to • Some can tolerate much higher temperatures Pressure tolerant bacteria for use in bioreactors can develop antibiotic resistance. without their enzymes becoming denatured. be formed by genetic engineering techniques. • Antibiotics will then kill ‘sensitive’ bacteria and favour • Low temperatures slow down the rate of reaction of resistant bacteria. enzymes resulting in slower growth Economic importance of • Bacterial strains have emerged which are resistant to almost all known antibiotics (multi-resistant). As 2. pH bacteria a result present day antibiotics become ineffective. MRSA is one example. • If a bacterium is placed in an unsuitable pH its Beneficial bacteria enzymes will become denatured • Bacteria such as Lactobacillus are used to convert milk to products such as cheese and yoghurt 3. Oxygen concentration • Genetically modified bacteria e.g. E. Coli are used to Misuse of Antibiotics make products such as insulin, enzymes, drugs, food flavourings and vitamins • Aerobic bacteria require oxygen for respiration e.g. Overuse of antibiotics Streptococcus • Antibiotics can be formed by some microorganisms • Bacteria in the colon help produce vitamins • This is why oxygen is sometimes bubbled through • This results in the increased • Bacteria are active in the Carbon and Nitrogen bioreactors growth of antibiotic resistant Cycles • Anaerobic bacteria do not require oxygen to respire bacteria o Facultative anaerobes can respire with or • Failure of some patients to Harmful bacteria without oxygen e.g. E. Coli (found in intestines) complete a course of • Pathogenic micro-organisms cause disease in plants o Obligate anaerobes can only respire in the antibiotics prescribed to and animals, e.g. tuberculosis, pneumonia, etc. absence of oxygen e.g. Clostridium tetani them by a doctor allows the • If they enter the body through a wound they can (causes tetanus) bacteria to survive and re- multiply and effect the nerves and activity of muscles grow • Bacteria can cause food spoilage and tooth decay. www.mrcbiology.com 3.1.10.H Growth Curves Rate of Growth The Stationary Phase • Bacteria divide by Binary Fission. • The rate of growth levels off during this period. Bio-processing • This is a form of asexual reproduction. • This is because: Involves the use of living organisms to produce a wide • Under ideal conditions it can take place every 20 o The nutrients are becoming used up. range of products, e.g. yoghurts, cheeses, vitamins, minutes! o The amount of waste produced by the bacteria alcohol products such as wines and beers, etc. • In this way huge numbers of bacteria can be themselves is increasing. There are two main methods of food processing: produced very rapidly. o The rate at which new cells are produced is • Batch food processing • Because of this we use a special scale called the equal to the rate at which other cells are dying. • Continuous flow food processing logarithmic scale to represent their numbers, i.e. 100, 101, 102, 103, 104, 105... OR The Death (Decline) Phase Batch food processing 1, 10, 100, 1,000, 10,000, 100,000 ... During this phase more bacteria are dying than are A fixed amount of sterile nutrient is added to the micro- being produced. This is because: organisms in the bioreactor. • Very few nutrients are left. Growth curve for Bacteria The micro-organisms go through the stages of a typical Lag Log Stationary Death • Many bacteria are poisoned by the waste produced phase Phase Phase growth curve, i.e. The Lag, Log, Stationary and Death Phase by such large numbers phases • Thus the rate of growth is falling. Although the reaction may be stopped before the death phase as very little product will be formed at this stage. Endospore Formation In unfavourable conditions many bacteria can form In Batch Processing most of the product is formed during the Log and Stationary phases Bacteria Number of Number endospores These are highly resistant to drought high temperature Logarithmic Scale Logarithmic and other environmental hazards. At the end of production: • The product is separated and purified. Time How Endospores are formed: • The bioreactor is cleaned and re-sterilised. The Lag Phase • The bacterial chromosome replicates. • The process can then be repeated. • After inoculation there is normally a brief period of • One of the new strands becomes enclosed by a adaptation by the cells to the new conditions. tough-walled endospore formed inside the parent Continuous Flow food processing • Bacteria are producing the enzymes necessary to cell. • Nutrients are continuously fed into the bioreactor. digest the nutrients. • The parent cell then breaks down • At the same time the culture medium (containing • The rate of growth begins to increase towards the • Endospores can remain dormant for a long period of some micro-organisms) is continually withdrawn. end of this phase. time. • Micro-organisms are maintained in the Log phase of • When conditions are favourable a new bacterium growth and the process can continue uninterrupted The Log (Logarithmic OR Exponential) Phase can be formed again and continue to reproduce. for weeks, even months. • There is a rapid period of growth during this phase • Factors such as temperature, pH, rate of stirring, due to the fact that: Batch and Continuous Flow concentration of nutrients, oxygen and waste • Bacteria have developed the necessary enzymes products are constantly monitored in order to and there are plenty of nutrients. Food Processing maintain growth and produce the maximum yield. • There are few waste products being produced. • The rate of cell division is currently at its maximum A bioreactor is a vessel in which biological reactions In Continuous Flow Processing most of the product is with the number of bacteria doubling as often as take place formed during the Log phase every 20 minutes. .