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1、Chapter 8Chapter 8 The Growth of The Growth of MicroorganismsMicroorganisms Binary fission DNA replication complete, exact copy of chromosome Growth of cell synthesis of macromolecules increase in mass and size Binary fission Chromosomes attached to membrane Membrane growth chromosomes move apart Bi
2、nary fission Septum formation inward formation membrane cell wall Formation of two cells membrane and cell wall pinch off to form septum Forms of Asexual Reproduction Budding Small cellular extension (bud) Fragmentation Cyanobacteria range 0-20oC, optimum 15oC a. Cell membrane have high levels of un
3、saturated fatty acids remain semi- fluid in cold Psychrotrophs temp. range 0-35oC, optimum range 20-30oC Mesophiles temp. range 10-48oC, optimum range 25-40oC; max. 45oC; pathogenic growth at human body temperature (370C) Thermophiles temp. range 40-85oC, optimum 55-65oC, min. a. Eukaryotes are not
4、known to grow in environments above 60oC b. Thermophiles survive higher temps. by producing enzymes rapidly, thereby replacing damaged enzymes quickly Extreme Thermophiles temp. range 65-110oC, optimum 85-100oC (Archea) pH Exhibit a wide range of environmental pH tolerances, maintain an intracellula
5、r pH of about 7.5 1. Bacteria have an optimum pH for growth between 6 and 8; minimum and maximum pH for growth are about 4 and 9, respectively 2. Acidophiles have an optimum pH of 4 and below (as low as 1) a. Alkaliphiles pH as high as 12 3. Molds and yeasts have an optimum pH between 5 and 6 4. Pro
6、tozoa have an optimum pH between 6.7 and 7.7 5. Algae have an optimum pH between 4 and 8.5 Other Conditions Osmotic pressure the pressure from water moving across cytoplasmic membrane from an area where water is in greater concentration to an area of its lower concentration a. Plasmolysis when conce
7、ntration of medium exceeds the concentration inside, the cytoplasm shrinks Halophiles salt lovers-extremely high salt concentration (Archaea) Barophiles adapted to environments with relatively high hydrostatic pressure. Gaseous Atmosphere 1. Aerobic Microorganisms oxygen concentrations (21%) are suf
8、ficient for growth a. Aerobes can chemically extract more energy from nutrients than anaerobes 2. Facultative Microorganisms grow in the presence (aerobic) or absence (anaerobic) of oxygen. Under anaerobic conditions, energy is produced by fermentation. a. Microaerophiles 2-10% O2 Gaseous Atmosphere
9、 3. Anaerobic Microorganisms cannot survive in presence of oxygen a. Obligate (strict) cannot tolerant oxygen, is killed by it b. Toxicity of oxygen is due to the production of superoxide radicals (O2-) c. Superoxide radicals give rise to hydroxyl radicals (OH- ), which destroy cell components such
10、as DNA d. Production of superoxide and hydroxyl radicals occurs by the following reactions: (SO by-product of metabolisms; ) O2 + e- O2-superoxide radical 2O2- + 2H+ O2 + H2O2hydrogen peroxide O2- + H2O2 O2 + OH- + OH+hydroxyl radicals (reacts w/ iron complexes) e. Aerobic and facultative microorgan
11、isms have developed mechanisms and/or enzymes to neutralize superoxide radicals Gaseous Atmosphere 1. Some produce superoxide dismutase (SOD), which converts the radical to hydrogen peroxide: O2- + O2- + 2H+ H2O2 + O2 2. Some produce catalase, which converts hydrogen peroxide to water and oxygen 2H2
12、O2 2H2O + O2 3. Some produce peroxidase, which converts hydrogen peroxide to water H2O2 + 2H+ 2H2O Table 8.1 Relationships of Various bacteria to Oxygen Microbial ClassResponse to O2CatalaseSuperoxide Dismutase Example Obligated aerobesRequires oxygenPresentPresentP. aeruginosa Facultative anaerobes
13、Can grow with or without oxygen PresentPresentE. coli MicroaerophilesGrow best with low oxygen PresentPresentCamp.jejuni Aerotolerant anaerobes Grow without oxygen, but not killed by it AbsentPresentStrep. pneumoniae Obligate anaerobesKilled by oxygenAbsentAbsentMethanococcus vannielli Measuring gro
14、wth Mass dry weight non-living culture Turbidity cells in broth higher turbidity = greater cell number Measuring Microbial Growth A. Measuring Mass of cells in population 1. Dry weight cells in oven at 1050C for 24 hours a. Separate cells from medium 1) Centrifugation 2) Desiccators 2. Turbidity Fig
15、ure 8.7, p.215 B. Counting number of cells in population 1. Total count a. Counting chamber Figure 8.8, p.216 b. Turbidity c. Viable cell count 1) Plate count Figure 8.9, p.217 2) Filtration count Figure 8.10, p.218 3)Most probable number (MPN) Measurement of turbidity Spectrophotometer measures absorbance of light by cells in broth culture standard curve of cell/ml vs absorbance Total cell counts Counting chamber Petroff-Hauser known depth squares of known dimensions count cells specific squares determine number of cells per volume viable stain distinguish live and dead cell
