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Microbial GrowthF08 - M I CROBI AL GROWT H Cha pter 6 About...

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MI CROBI AL GROWTH Chapter 6
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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
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GROWTH REQUI REMENTS Obligate vs facultative : Obligate: must have the specific environment Facultative: able to adjust to fluctuations or a range of environmental factors PHYSICAL REQUIREMENTS 1. pH 2. TEMPERATURE 3. OSMOTIC PRESSURE BIOCHEMICAL REQUIREMENTS 1. C and N sources 2. H 2 O and Oxygen requirements 3. Organic growth factors & trace minerals
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TEMPERATURE Temperature range Minimum, OPTIMUM, Maximum Psychrophiles : cold loving 0-15 ° C Optimum: 15 - 30 ° C Psychrotrophs: mainly responsible for food spoilage Mesophiles : moderate temp. loving 10-47 ° C Optimum: 25-45 ° C Thermophiles : heat loving 40-80 ° C Optimum: 50-60 ° C Extreme thermophiles: 65-110 ° C
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Figure 6.1 Typical Growth Rates and Temperature
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pH BUFFERS : stabilizes pH of a solution Able to take up or donate H + to the solution OPTIMUM for most bacteria = pH 6.5-7.5 Normal human physiological pH 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
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3. OSMOTI C 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, water leaves the cell Preserve foods because growth is inhibited HYPOTONIC solution: conc. of solutes inside > outside HALOPHILE - salt loving Extreme halophile (30% NaCl) - Archaea Facultative halophile (2 % NaCl)
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Figure 6.4 Plasmolysis
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