<p> MICROBIAL GROWTH Chapter 6 About GROWTH...... • Usually means an increase in size however….. • Microbes grow by increasing in number and not in size • They can accumulate into clumps of hundreds and colonies of thousands • COLONIES = large number of microbes usually derived from one organism (clone) • Unicellular organisms do grow in size but ONLY until the mother cell doubles in size and duplicates its contents • The mother cell divides into 2 new daughter cells • This process is called binary fission GROWTH REQUIREMENTS – Obligate vs facultative: – Obligate: must have the specific environment – Facultative: able to adjust to fluctuations or a range of environmental factors • PHYSICAL REQUIREMENTS – pH – TEMPERATURE – OSMOTIC PRESSURE • BIOCHEMICAL REQUIREMENTS – C and N sources – H2O and Oxygen requirements – Organic growth factors & trace minerals 1. pH • BUFFERS: stabilizes pH of a solution – Able to take up or donate H+ to the solution • OPTIMUM for most bacteria = pH 6.0-8.0 – Best if between 7.2 – 7.6</p><p>• Normal human physiological pH</p><p>• Neutrophiles • ACIDOPHILES - can grow at low pH – Lower than pH 4.0 • ALKALIPHILES - can grow at high pH • OPTIMUM for yeast = pH 4.0 - 5.0 2. TEMPERATURE • Temperature range – Minimum, OPTIMUM, Maximum • Psychrophiles: cold loving 0-35 C – Optimum: 15 - 30 C • Mesophiles: moderate temp. loving  10-47 C – Optimum: 28-45 C • Thermophiles: heat loving  40-80 C – Optimum: 55-75 C – Extreme thermophiles: 65-110 C 3. OSMOTIC PRESSURE • Force with which a solvent moves from a solution of lower solute concentration to solution of higher solute concentration • HYPERTONIC solution: conc. of solutes outside > inside – Plasmolysis occurs – Preserve foods • HYPOTONIC solution: conc. of solutes inside > outside • HALOPHILE - salt loving – Extreme halophile (30% NaCl) - Archaea – Facultative halophile (2 % NaCl) BIOCHEMICAL REQUIREMENTS • Each organism has it’s own range of nutritional requirements in addition to its physical needs • Can be classified based on carbon source • Can be classified based on amount of oxygen needed • Each organism differs in it’s requirements for nitrogen, sulfur and phosphorous sources or requirements for other trace elements CARBON SOURCE • Carbon = structural backbone of all living matter • Chemoheterotrophs: – C and energy derived from organic compounds like proteins, carbohydrates and lipids • Chemo- & photoautotrophs: C from CO2 – Chemoautotrophs get their energy from inorganic compounds – Photoautotrophs get their energy from sunlight NITROGEN • USES – Amino acids/proteins – Nucleic acids: DNA, RNA – ATP • SOURCES – Breakdown of protein containing materials – + - Ammonium ions (NH4 ) and nitrate ions (NO3 ) • NITROGEN FIXATION: – Process where an organism is able to N from gaseous N2 – Cyanobacter – Rhizobium: Symbiotic relationship with plants SULFUR • USES – Amino acids: Cysteine, Methionine – Vitamins: Thiamine, Biotin • SOURCES – Sulfur containing compounds such as S-containing amino acids and inorganic sulfate salts & some vitamins – 2- SO4 – H2S PHOSPHOROUS • USES – Nucleic acids: DNA, RNA – ATP – Phospholipids • SOURCES – 3- PO4 Trace Elements & Organic Growth Factors • ESSENTIAL = can not synthesize therefore MUST BE SUPPLIED • TRACE ELEMENTS – Essential cofactors/coenzymes – K, Fe, Cu, Mb, Zn • Vitamins • Amino acids • Purines • Pyrimidines OXYGEN - • USEFUL: respiration final e acceptor</p><p>• HARMFUL: strong oxidizer</p><p>• OBLIGATE AEROBES - require O2 to live – Use O2 as final electron acceptor – Contain enzymes that detoxify excess molecular oxygen</p><p>• FACULTATIVE AEROBES - can use but does not require O2</p><p>• OBLIGATE ANAEROBE - unable to use O2 – Lack detoxifying enzymes</p><p>• AEROTOLOERANT ANAEROBE - does not use O2 but can grow in it’s presence (1 – 2% O2)</p><p>• MICROAEROPHILE - requires less O2 – Needs 5-10% CO2 to initiate growth O2 : Good or Bad? • Reactive and Toxic byproducts – Highly unstable allowing them to steal electrons from nearby molecules – Singlet Oxygen – .- Superoxide free radical (O2 ) – -2 Peroxide (O2 ) – Hydroxyl • Detoxifying enzymes – SOD: Superoxide dismutase .- + • Converts 2 O2 + 2H  O2 + H2O2 – Catalase</p><p>• Converts H2O2  O2 + 2 H2O – Peroxidase + • Converts H2O2 + 2H  2 H2O BACTERIAL GROWTH & DIVISION • GROWTH = orderly process of the increase in the number of individual microbes – There is an increase in size followed by cell division – BINARY FISSION - most bacteria divide in this manner – Some yeast replicate by budding – new cell is smaller than mother cell • DIVISION = 4 steps for 1 cell to divide into 2 cells – Elongation of cell and DNA duplication – Cell wall & plasma membrane increase and start folding inward – Formation of cross wall between DNA regions – Cells separate into 2 new identical cells GENERATION or DOUBLING TIME • Length of time required for a generation of cells to divide (double) • Length of time will vary: – Depends on particular organism – Depends upon environmental factors – Minutes to hours (usually less than 1 hour) • Because they double in number at every division it is difficult to plot cell numbers using arithmetic numbers – Usually use a logarithmic scale to graph bacterial growth</p><p>Bacterial Growth Curve • Four phases for bacterial growth if an old culture  fresh medium • LAG – Increase in cell size and division – Intense increased metabolic activity – Sensitive to physical & chemical damage • LOG/EXPONENTIAL – Maximal growth and cell division</p><p>• Cells doubling at the fastest rate</p><p>• Cell size is slightly decreased – Increased metabolic activity – Sensitive to physical & chemical damage Bacterial Growth Curve (cont) • STATIONARY – Growth rate eventually decreases then stops – # of new cells = # of dead cells – Nutrient depletion – Metabolic byproducts • DEATH (DECLINE) – Whole culture dies at first slowly then exponentially MATH: Arithmetic vs Logarithmic • PLOT: Cell # vs Generations • n CALCULATIONS: Mf = (Mi) 2</p><p>M f= final number of bacteria</p><p>M i= initial number of bacteria – n = number of generations</p><p>• If know any 2 of the 3 above numbers we can solve </p>