a tiny bit of microbiology eve 430. summary of nutritional groups
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A Tiny Bit of Microbiology
EVE 430
Summary of nutritional groups
Growth and Reproduction of Bacteria – Binary Fission
• Bacteria basically clone themselves when they reproduce
• Binary fission• The circular DNA
molecule is replicated; then the cell splits into two identical cells, each containing an exact copy of the original cell's DNA
Rod-Shaped Bacterium, E. coli, dividing by binary fission
Rod-Shaped Bacterium, hemorrhagic E. coli, strain 0157:H7
(division)
Asexual Reproduction by Budding
• Budding yeast• 1. Cell wall bulges out• 2 & 3. Nucleus
divides by mitosis• 4. One nucleus
migrates to bud• 5. Bud cell wall forms
and bud breaks off
Asexual reproduction by budding
Microbial Population Growth
• Microbial populations grow exponentially when supplied with enough nutrients…….
• The time it takes to divide is called the generation time
Kinetics of Microbial Population Growth
End of Log phase is brought about by:
• Exhaustion of limiting nutrient
or
• Build up of toxins (e.g. alcohol in yeast cultures)
For continuous exponential growth
• Continuous culture techniques
• Chemostat
Factors affecting Microbial Growth
• Temperature• Substrate Concentration• pH• oxygen concentration• pressure
• In nature competition for nutrients (and space), predation and parasitism limit the exponential growth of microbes.
Variations in temperature optima
Affect of substrate concentration on
enzyme activity (or Microbial growth) The Monod model
0
1
0 Substrate concentration S [g/L]
qS
[g
/gh
]
qSmax
KS
SSS KS
Sqq
max
Diff microbes have diff pH optima:
• Acidophiles = acid pH optimal (1 to 5.5)
• Neutrophiles = pH 5.5 to 8 optimal
• Alkaliphiles = pH 8.5 to 11.5 • Extreme alkaliphiles =
optimum pH 10 or greater • Note: most bacteria are
neutrophiles (Exceptions: some bact in hot springs have optimum of 1-3)
• Most fungi prefer slight acid (pH 4 to 6)
Environmental Factors that Influence Microbial Growth