microbioLAB #6: Environmental Factors Affecting Growth of Microorganisms

Mt 2

The growth of microorganism is affected by the environmental factors such as:

- temperature 

- pH 

- osmotic pressure

- nature 

- chemicals

By changing this factors (temp, pH, osmotic pressure, nature, chemicals) one can:

- maximize microbial growth

- inhibit or delay the growth of unwanted microorganisms

Each microbe requires a specific growth temperature—

• which is determined by what

• name examples

- range which is determined by the heat sensitivity of it’s particular -components such as ex. Enzymes, Membranes and Ribosomes

Every microbe has three key temperature points (known as cardinal temperatures) that dictate its survival. what r they?

• Minimum-lowest temperature at which growth can occur

• Maximum-Highest temperature at which growth can occur

• Optimum-Temperature at which rate of cellular reproduction is most rapid

  • Is similar to temperature of normal habitat

  • Example: pathogenic Bacteria in human: optimum temperature is 35-37 degrees Celsius like that of human blood.

Depending on their preferred optimum temperatures, bacteria are grouped into five main types:

1. psychrophiles

2. phychrotrophs

3. mesophiles

4. thermophiles

5. hyperthermophiles

psychrophiles

Cold-lovers that grow well at 0°C and have an optimum of 15°C or lower.

Psychrotrophs

Facultative psychrophiles; grow at 0 -7 degrees Celsius

Mesophiles

Middle-temperature lovers Growth optima 25-45 degrees Celsuis. Majority of bacterial species are in

group 25-45 degrees Celsius

thermophiles

Heat-lovers tht grow at 90 degrees or above.

thermoduric:

bacteria that can survive boiling even though they cannot grow.

* Usually they are spore forming

whts this an image of?

THERMODURIC: B. subtili

pH affects prokaryotic growth by affecting activity of ____. Especially those that are involved in ____

1. enzymes

2. biosynthesis (building cellular parts)

Environmental Factor pH:

which ranges do acidophiles, neutrophiles and alkaliphiles thrive in?

most bacteria r in what grp and produce what acids?

what do scientists do when growing them?

• Acidophiles thrive under highly acidic conditions (usually at pH 2.0 or below

• neutrophiles thrive in neutral pH environment 6.5 and 7.5

• most bacteria r neutrophiles and produce metabolic acids

  • scientists, when they grow them, often add buffers (like peptones or phosphate salts) to growth media to soak up those/neutralize acids and keep the pH stable (produce pH equilibrium)

• alkaliphiles thrive in basic or alkaline environments, (pH ~8.5-11) environments optimally around pH of 10

pH

Environmental Factor Osmotic pressure

1. what is diffusion?

2. ____ is the diffusion of water

3. osmotic pressure is the force developed when?

• Diffusion is movement the movement of small substances from a higher to lower concentration.

• Osmosis is the diffusion of water

• Osmotic pressure is the force developed when two solutions of different solute concentration are separated by a membrane that is permeable only to the solvent

  • Solvent: Liquid

  • Solute: Substance

1. isotonic soln

2. hypotonic soln

3. hypertonic soln

• Isotonic solution: the concentration of the solute is the same inside and outside the bacterium

• Hypotonic solution (low solute, high water content), water will enter the cell and cause it to burst.

• Hypertonic solution (high solute, lower water content), water leaves and the plasma membrane shrinks away from the wall - plasmolysis

cells with cell wall.

wht kind of soln is this (iso,hypo,hypertonic)?

isotonic

cells with cell wall.

wht kind of soln is this (iso,hypo,hypertonic)?

hypotonic

cells with cell wall.

wht kind of soln is this (iso,hypo,hypertonic)?

hypertonic

distinguish graph

Based on tolerance to salt, we distinguish

• non halophile: grows at less than 1% salt concentration

• Halotolerant: grows at salt concentration from 0-10%

• halophile: microbe that can tolerate high salt (NaCl) concentrations (halo means salt)

• Moderate halophile: live at 4.7 to 20% salt

• Extreme halophiles: tolerate 20 to 30% salt concentration