Transcript The Requirements for Growth

Chapter 6
Microbial Growth
The Requirements for Growth: Physical Requirements
• Temperature
• Minimum growth temperature
• Optimum growth temperature
• Maximum growth temperature
Temperature
Celcius to fahrenheit conversion
Figure 6.1
• Psychrophiles: cold-loving microbes
• Psychrotrophs (“moderate psychrophiles”): cold
tolerant; cause food spoilage
• Mesophiles: moderate-temperature-loving
microbes
• Thermophiles: hot-loving microbes
Figure 6.2
The Requirements for Growth: Physical Requirements
• pH
• Most bacteria grow between pH 6.5 and 7.5
• Molds and yeasts grow between pH 5 and 6
• Acidophiles
• Alkalophiles
• neutralophiles
The Requirements for Growth: Physical Requirements
• Water - (osmotic pressure)
• Hypertonic environments can cause plasmolysis
• Extreme or obligate halophiles require high [salt]
• Facultative halophiles tolerate high [salt]
• Hypotonic environment may cause cells to burst
Figure 6.4
The Requirements for Growth: Chemical Requirements
• Carbon
• Form structural and functional organic molecules;
energy source
• Heterotrophs
• Autotrophs
The Requirements for Growth: Chemical Requirements
• Nitrogen
• Used to make amino acids (proteins), nucleic acids
• Bacteria acquire nitrogen from various sources:
• Most by decomposing proteins
• Some bacteria use NH4+ (ammonium), NO3
(nitrate), or N2 (nitrogen gas)
The Requirements for Growth: Chemical Requirements
• Sulfur
• Is used to make some amino acids, thiamine, biotin
• Bacteria acquire sulfur from various sources:
• Most bacteria decompose proteins
• Some bacteria use SO42 (sulfate) or H2S
• Phosphorus
• Is used to make DNA, RNA, ATP, and membranes
The Requirements for Growth: Chemical Requirements
• Trace Elements
• Inorganic elements required in small amounts
• Usually as enzyme cofactors
The Requirements for Growth: Chemical Requirements
• Organic Growth Factors
• Organic compounds that the microbe cannot
synthesize
• Obtained from the environment
• Vitamins, amino acids, other compounds
The Requirements for Growth: Chemical Requirements
• Oxygen (O2)
obligate
aerobes
Facultative
anaerobes
Obligate
anaerobes
Aerotolerant
anaerobes
Microaerophiles
Culture Media
• Medium: Nutrients prepared for microbial growth
• Sterile: No living microbes
• Inoculation: Introduction of microbes into medium
• Inoculum: the microbes used to inoculate a medium
• Culture: Microbes growing in/on a medium
Agar
• Complex polysaccharide
• Used as solidifying agent for culture media in Petri
plates, slants, and deeps
• Generally not metabolized by microbes
• Liquefies at 100°C
• Solidifies ~40°C
Culture Media
• Chemically Defined Media: Exact chemical
composition is known
• Complex Media: Extracts and digests of yeasts, meat,
or plants
• i.e. Nutrient broth
• i.e. Nutrient agar
• Extract: water soluble preparation of broken down cells
• Digest: water soluble preparation of partially broken down proteins
Culture Media
Table 6.2 & 6.4
Anaerobic Culture Methods
• Reducing media
• Contains thioglycolate that combines with O2
•
http://www.mc.maricopa.edu/~johnson/labtools/Dbiochem/oxy.html
• Oxyrase – commercial product that reduces O2 to
H2O (removes the oxygen)
Anaerobic Culture Methods
• Anaerobic
jar
• Chemical
reactions
remove
oxygen
Figure 6.5
Capnophiles require high CO2
• Candle jar
•CO2-packet
Figure 6.7
Selective Media
• Suppresses unwanted microbes and allows desired
microbes.
• How? i.e. vary the [salt] or pH
• (Enrichment Media: encourages growth of microbes
present in small numbers and/or are fastidious)
• Fastidious: require specific nutrients
• How? Use special ingredient
Differential Media
• Make it easy to distinguish
colonies of different microbe
types.
• How?
• i.e. hemolysis on blood agar
• i.e. mannitol fermentation
• i.e. pH indicator (color)
Pure Culture
• A pure culture contains only one species or strain
• A colony is a population of cells arising from a single
cell or spore or from a few attached cells
• A colony = colony-forming unit (CFU)
Preserving Bacterial Cultures
• Deep-freezing: -50°C to -95°C
• Lyophilization (freeze-drying): Frozen (-54° to -72°C)
and dehydrated in a vacuum; stored at room temp.
• Bacteria can be preserved for years by these methods
Reproduction in Prokaryotes
• Binary fission
• Budding
•Microbial growth = increase in number of cells, not cell size
Generation Time
• The time period for one cell to divide; therefore, for the
population to double
• Generation time varies from microbe to microbe
• E.coli = 20 – 30 minutes
• Mycobacterium tuberculosis = 15 – 20 hours
Figure 6.14
Direct Measurements of Microbial Growth
• Plate Counts: Perform serial dilutions of a sample
Figure 6.15, top portion
Plate Count
• After incubation, count colonies on plates that have 25250 colonies (CFUs)
Figure 6.15
Direct Measurements of Microbial Growth
• Filtration: used for small population samples
• i.e. Waste water treatment testing
Figure 6.17a, b
Direct Measurements of Microbial Growth
Figure 6.19
Indirect Measurements of Microbial Growth
• Measuring turbidity of culture using a
spectrophotometer
Figure 620