Microbial Growth PDF

www.udst.edu.qa BIOL2010 Week 4 - Microbial Growth Microbial Growth As we know, microbes reproduce using binary fission Sometimes use budding to produce offspring. Budding is used by yeasts to produce offspring Growth increases the size of the organis...

www.udst.edu.qa BIOL2010 Week 4 - Microbial Growth Microbial Growth As we know, microbes reproduce using binary fission Sometimes use budding to produce offspring. Budding is used by yeasts to produce offspring Growth increases the size of the organism An increase in size enables the formation of multiple organisms Bacteria go through non-synchronous growth Factors Affecting Microbial Growth Rate pH – Every microbe has an optimum pH in which they will grow Acidophiles like acidic conditions (pH 1.0 – 5.4) Neutrophiles (pH 5.4 – 8.0) Alkaliphiles prefer basic conditions (pH 7.0 – 11.5) Factors Affecting Microbial Growth Rate Temperature – All organisms have an optimal growing temperature Thermophiles – grow best at high temperatures (50 – 60 C. Max 113C) Mesophiles – grow best at moderate temperatures (20 – 40 C. Max 45C) Psychrophiles – grow best at low temperatures (10 -20 C. Max 30C) Factors Affecting Microbial Growth Rate Osmotic Pressure – Optimum level of solutes at which organism can survive Halophiles – can withstand high osomarlity – hypertonic conditions Moisture – Require some level of moisture – some can sporulate Barometric pressure – Barophiles – high barometric pressure Factors Affecting Microbial Growth Rate – Oxygen Requirements Classification by oxygen Characteristics Growth Pattern demand Cannot respire or ferment Obligate aerobe Top of TT anaerobically, must have oxygen. Obligate anaerobe Poisoned by oxygen. Bottom of TT Can metabolize aerobically or Facultative anaerobe anaerobically. Aerobic metabolism is Mostly at top of TT more advantageous. Need oxygen in lower Upper TT, but not Microaerophiles concentrations. Will be poisoned by the top high oxygen levels Do not require oxygen, but not Aerotolerant Anaerobes Throughout the TT poisoned by it. Factors Affecting Microbial Growth Rate – Oxygen Requirements Bacterial Growth Major assumption is that colonies grow from a single bacterial cell: Cell goes through repeated binary fission and grows a colony All cells come from an original cell and are genetically identical Growth in colonies is non synchronous Synchronous Vs. Non-Synchronous Growth Log phase can be described in two manners: Synchronous growth – All cells in the culture divide at the same time Non synchronous growth – all cells in the culture divide during the generation time (more plausible) Bacterial Growth The Bacterial Growth Curve: Bacterial populations exhibit a characteristic four phases in growth: 1. Lag phase 2. Log phase 3. Stationary phase 4. Death phase Lag Phase This cycle is considered to be the standard bacterial growth curve Lag phase – Little or no cell division Post introduction of the species into the growth media Organisms are metabolically active Grow in size but not in numbers Cell numbers remain fairly constant Log Phase Log phase – bacterial division is increased Cells divide and grow at a rapid rate The interval is called generation time This is the time required for the cell to divide: population doubles Log Phase During log phase, several conditions emerge: Available nutrients decrease Wastes accumulate Living space becomes less The ability to produce energy and divide diminishes Growth rate slows Stationary Phase During stationary phase, the population stabilizes: The number of new cells produced equals the number of cells dying Lack of nutrients prevents positive population growth The number of living cells stays constant Death Phase During death phase, the population begins to decline: The number of new cells produced is less than the number of cells dying Conditions become worse nutrition wise Cells cannot divide and begin to die Nutrition is gone Standard Bacterial Growth Curve