Topic 5: Microbial Growth Flashcards
Chemical Requirements for Microbial Growth NCHOPS Nemonic: Nice Chops Totally Organic
Nitrogen (N) Carbon (C) Hydrogen (e.g. H20) Oxygen (O) Phosphorous (P) Sulphur (S) Trace Elements (eg Fe, Mg, Cu, Zn, Co) Organic Growth Factors (eg Vitamins)
Physical Requirements for Microbial Growth
Temperature pH Osmotic Pressure
5 Main Groups of Microbes Classified by Temperature.
Microbes increasing from cold to hot. Psychrophiles Psychrotrophs Mesophiles Thermophiles Hyperthermophiles
Microbes and pH
Most Bacteria grow between pH of 6.5 and 7.5 Moulds and yeast grow between a pH of 5 and 6 Acidophiles grow in acidic environments Alkaliphiles grow in alkaline environments In media pH is controlled by buffers.
Microbes and Osmotic Pressure
Hypertonic environments, or an increase in sugar or salt cause plasmolysis. Most micro organisms inhibited by high salt (10-15%) and sugar (50-70%) Halophiles love salt environments Saccharophiles love sugar environments Extreme halophiles require high osmotic pressure Facultative halophiles can tolerate high osmotic pressure.
Chemical Requirements NCHOPS
96% dryweight of a bacterial cell is composed of the following elements. Nitrogen: Amino Acids, Proteins, DNA, RNA Carbon: Carbohydrates, lipids, amino acids, DNA and RNA. Carbon also used for catabolism and anabolism Oxygen:`Found in most organic molecules and as terminal electron acceptor. Phosphorous: Found as Phosphate, written Pi, needed for ATP, NADP, DNA and RNA Sulphur: Needed for amino acids M and C cofactors
Trace Elements
Inorganic elements required in small amounts 1. Iron needed for cytochromes in electron transport 2. Magnesium: counter iron for nucleotides and ATP; also a cofactor in a number of enzymes. 3.Zinc 4.Cobalt 5.Copper 6.Molybdenum Many 2+ ions are enzyme cofactors
Toxic Oxygen
Singlet Oxygen: O2 boosted to a higher energy state Superoxide free radicals: O2- O2^-+O2^-+2H^+ —Superoxide disutase—> H202+O2 Peroxide Anion: O2^2- 2H2O2—-Catalase–>2H2O+O2 H2O2+2O^+—–Peroxidase–>2H20 Hydroxyl radical (OH*)
Oxygen and Growth
- Obligate Aerobes - require oxygen. Top of Test Tube. 2. Facultative Anaerobes produce energy with or without oxygen. Dispersed throughout tube greater mass at top. 3.Obligate Anaerobes - Require absence of oxygen. Bottom of tube 4.Aerotolerant Anaerobes - can grow with oxygen, but prefer it’s absence. Dispersed throughout tube evenly 5. Microaerophiles - Requires oxygen to survive but requires environments with oxygen content lower than the atmosphere. Middle of tube.
Organic Growth Factors
1.Organic compounds obtained from the environment. 2.Vitamins, amino acids, purines and pyrimidines 3. Some microorganisms require a certain vitamin (Growth Factor) 4. Many Bacteria do not require any growth factors
Culture Media
Culture Medium: Nutrients prepared for microbial growth Sterile: Contains no living organisms Inoculum: Microbes introduced into medium Culture: Microbes growing in/on culture medium. Pure culture: Contains only one species or strain. Colony: Population of cells arising from a single cells or spore or from a group of attached cells. Colony forming unit (CFU): Measure of the number of living (viable) cells in a sample that will grow, divide and form colonies on solid media, such as agar plates.
Agar
1.Complex polysaccharide made from Agar- Agar seaweed (algae) 2.Used as solidifying agent for culture media in petri dishes, slants and deeps. 3. Generally not metabolised by microbes. 4.Liquefies at 100 degrees Celsius. 5. Solidifies at 40 degrees Celsius. 6. Highly purified agar = agarose
Define Media
A. Chemically defined media for bacterial growth: Exact Chemical composition known. B. Complex Media for bacterial growth: Beef extract and peptone do not have defined chemical compositions, they vary from peptone to peptone. C. Selective Media Suppress unwanted microbes and encourage desired growth. e.g. penicillin D. Differential Media: An indicator in the medium allows detection of a bacterial trait. e.g. blood in growth medium. E. Enrichment Culture: Encourages growth of desired microbe
Anaerobic Media
- Chemicals such as cysteine, thioglycolate or sulphide are O2 reactive 2. They can be added to remove O2 by reaction 3. Also, O2 has a lower solubility at higher temps, so boiling media before use reduces O2 partial pressure.
Anaerobic Chamber
1.Atmosphere physically and chemically stripped of O2. 2. Usually a device to measure and report O2 content in parts per million (ppm). 3.Atmosphere may be: *N2- almost inert *CO2 *H2- for catalytic conversion of any liberated O2 to water. Microbes such as Methanogens
