Microbial%20GrowthF08

Microbial%20GrowthF08 - MICROBIAL GROWTH Chapter 6 About...

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Unformatted text preview: 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 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 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 Figure 6.1 Typical Growth Rates and Temperature 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 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, water leaves the cell – Preserve foods because growth is inhibited • HYPOTONIC solution: conc. of solutes inside > outside •...
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Microbial%20GrowthF08 - MICROBIAL GROWTH Chapter 6 About...

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