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