Microbial Growth refers to

Increase in number of cells, not cell size.
*Populations
*colonies

The requirements for growth

* Physical requirements (there are 3)

1. Temperature
2. pH
3. Osmotic pressure

The requirements for growth

* Chemical Requirements (there are 5)

1. Carbon

2. Nitrogen, sulfur & phosphorous

3. Trace elements

4. Oxygen

5. Organic growth factor

Physical Requirements

Temperature
* MINIMUM growth temp
* OPTIMUM growth temp
* MAXIMUM growth temp

Psychrotrophs

* Grow between 0°C & 20-30°C
* Cause food spoilage

Food preservation temperatures

What temperatures is the danger zone?

Between 20°C to 50°C

* Rapid growth of bactera; some may produce toxins.

pH

Most bacteria grow between pH

6.5 & 7.5

pH

Molds and yeasts grow between pH

5 & 6

pH

Acidophile grow in _____ environments

acidic

Osmotic Pressure

Hypertonic environments, or an increase in salt or sugar, cause

Plasmolysis

Osmotic Pressure

_____ or ______ require high osmotic pressure

Extreme / obligate halophiles

Obligate →

requires

Facultative →

tolerate

Osmotic Pressure

_______ tolerate high osmotic pressure

Facultative halophiles

*(notice the word tolerate in the question)

Chemical Requirements

Carbon

* Structural organic molecules, energy source
* Chemoheterothrophs use organic carbon sources
* Autotrophs use CO2

Chemical Requirements

Nitrogen

* In amino acids & proteins
* Most bacteria decompose proteins
* Some bacteria use NH4+ or NO-3 (ammonia / Nitrates)
* A few bacteria use N2 in NITROGEN FIXATION

Chemical Requirements

Sulfur

* In amino acids, thiamine, & biotin
* Most bacteria decompose proteins
* Some bacteria use SO2-4 or H2S

Chemical Requirements

Phosphorus

* In DNA, RNA, ATP & membranes
* PO3-4 is a source of phosphorus

Chemical Requirements

Trace elements

* Inorganic elements required in small amounts
* Usually as enzyme cofactors

The effect of Oxygen on the growth of various types of bacteria

Obilgate Aerobes

* Only aerobic growth; oxygen required.
* Growth occurs on where high concentration of oxygen have diffused into the medium.
example: 1st tube at the left

The effect of Oxygen on the growth of various types of bacteria

Facultative Anaerobes

*Both aerobic & anaerobic growth; greater growth in presence of oxygen.
* Growth is best where most oxygen is present, but occurs through out tube.
example: 2nd tube from left

The effect of Oxygen on the growth of various types of bacteria

Obilgate Anaerobes

* Only anaerobic growth ceases in presence of oxygen.
* Growth occurs only where there is no oxygen
(bacteria clumped at bottom of tube)

The effect of Oxygen on the growth of various types of bacteria

Aerotolerant Anaerobes

*Only anaerobic growth, but continues in presence of energy.
*Growth occurs evenly; oxygen has no effect
example: 2nd to the last tube on right

The effect of Oxygen on the growth of various types of bacteria

Microaerophiles

*Only aerobic growth; oxygen required in low concentration.
*Growth occurs only where a low concentration of oxygen has diffused into medium.
example: very last tube on the right.