Bacterial Physiology & Growth (PDF)

Bacteria Growth and Physiology Dr. Mohamed Elmutasim Microbiology Department 26 Sep. 2022  Bacteria Growth Bacterial Reproduction: Bacteria reproduce by binary fission, a process by which one parent cell divides to form two progeny cells. ...

Bacteria Growth and Physiology Dr. Mohamed Elmutasim Microbiology Department 26 Sep. 2022  Bacteria Growth Bacterial Reproduction: Bacteria reproduce by binary fission, a process by which one parent cell divides to form two progeny cells.  Bacterial Growth Curve Exponential growth (logarithmic growth): one cell gives rise to two progeny cells The doubling (generation) time of bacteria: It is the time it takes for a population of bacteria to double in number. It ranges from 20 minutes for Escherichia coli to more than 24 hours for Mycobacterium tuberculosis. The growth cycle of bacteria has four major phases: 1- The lag phase: During which metabolic activity occurs but cells do not divide (few minutes up to many hours). 2- The log (logarithmic or Exponential ) phase: Rapid cell division occurs. β -Lactam drugs (e.g. penicillin) act during this phase because they are effective when cells are dividing. 3- The stationary phase: Nutrient depletion or toxic products cause growth to slow until no. of new cells balances no. of cells death resulting in a steady state. 4-The death phase: - Decline in the number of viable bacteria. Bacterial Growth Curve  Factors Influencing Bacterial Growth Physical Requirements Nutritional Requirements 1. Temperature 1- Energy source 2. Oxygen requirements 2- Carbon source 3. PH 3- Nitrogen source 4. Osmosis 4- Minerals - Sulfur - Phosphorus - Potassium, magnesium & calcium - Iron - Trace elements 5- Water 6- Growth factors  Factors Influencing Bacterial Growth: Physical Requirements 1-Temperature Definition Optimum growth temperature Psychrophiles Cold-loving bacteria Between – 5C and 15C. Mesophiles Bacteria that grow Between 20C and 40C. at moderate Most bacteria are temperatures. mesophilic & include soil bacteria and bacteria that live in and on the body. Thermophiles Heat-loving bacteria Between 45C and 70C. Hyperthermophiles Bacteria that grow Between 70C and 110 C. at very high temperatures  Physical Requirements 2- Oxygen requirements: Definition They obtain energy through Obligate aerobes Grow only in the presence of oxygen Aerobic respiration Microaerophiles - Require a low concentration of Aerobic respiration oxygen (2% to 10%) for growth - Higher concentrations are inhibitory Obligate anaerobes Grow only in the absence of oxygen - Anaerobic respiration (inhibited or killed by its presence). -or fermentation Aerotolerant - Cannot use oxygen to transform Only by fermentation anaerobes (obligate energy fermenters ) - Can grow in its presence. Facultative - Grow with or without oxygen -Aerobic respiration if anaerobes - But generally better with oxygen. oxygen is present Most bacteria - Fermentation or anaerobic respiration if it is absent. Physical Requirements  4- Osmosis Osmosis is the diffusion of water across a membrane: -From higher water concentration (lower solute concentration) -To lower water concentration (higher solute concentration) Osmosis does not require energy. 4- Osmosis Factors Influencing Bacterial Growth: Nutritional Requirements  Respiration: 1- Aerobic Respiration It is glucose catabolism under aerobic conditions. This results in energy production in the form of 38 ATP molecules. Aerobic respiration involves : The final electron acceptor is molecular O2 2- Anaerobic Respiration: It occurs in the absence of oxygen. The final electron acceptor is an organic molecule such as nitrate, sulfate, or CO2 The net yield of ATP molecules is less than it is with aerobic respiration.  3- Fermentation It is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates. It is the process by which facultative bacteria generate ATP in the absence of oxygen. 2- Carbon Source  3- Nitrogen Source Nitrogen Sources are: - Nitrogen - Nitrates - Ammonia - Organic nitrogen compounds Nitrogen is needed for the synthesis of: - Amino acids - DNA - RNA - ATP  4- Minerals 1. Sulfur: It is needed to synthesize sulfur-containing amino acids and certain vitamins. 2. Phosphorus: It is needed to synthesize phospholipids, DNA, RNA & ATP. Phosphate ions are the primary source of phosphorus. 3. Potassium, Magnesium and Calcium: These are required for certain enzymes. 4. Iron: It is a component of cytochromes and other enzymes. 5. Trace Elements: They are required in very minute amounts and function as cofactors (electron donors or acceptors) in enzyme reactions. They include sodium, zinc, copper, molybdenum, manganese, and cobalt ions. 5- Water & 6- Growth factors: Growth factors are organic compounds such as: - Amino acids - Purines - Pyrimidines - Vitamins Cells must have them for growth but cannot synthesize them. Fastidious Organisms: They have complex nutritional requirements & need many growth factors. Thank You