Theme 4 - Microbial growth

Microbial growth

Increases in the number of cells not cell size

Colonies

Group of cells large enough to be seen

What are the physical requirements for microbial growth

• Temperature

• PH

• Osmotic pressure

What are the chemical requirements for microbial growth

• carbon, nitrogen, sulfur and phosphorous

• Trace elements

• Oxygen

• Organic growth factor

What pH do most bacteria grow in

6.5 and 7.5

Acidophilus

Grow in acidic environments

What pH do moles and yeasts grow in

5 and 6

Osmotic pressure

Hypertonic environments or an increase in salt or sugar cause plasmolysis

What requires high somatic pressure ( 30% salt)

Extreme or obligate halophiles

What tolerates high osmotic pressure ( 2% salt )

Facultative halophiles

Why is carbon required

• energy source

• Chemoheterobtrophs use organic carbon sources

• Autotrophs use CO2

Why is nitrogen required

• can be used for nitrogen fixing from atmosphere

• NH4+ and NO3-

• In amino acids and proteins and most bacteria decompose proteins

Why is sulfur required

• Amino acids - thiamine and biotin

• Bacteria decompose proteins

• SO42- or H2S

What is phosphorus required for

• In DNA, RNA, ATP and membranes

• PO43-

What are trace elements required for

• inorganic elements in small amounts

• Enzyme cofactors

• Fe, Cu, Zn

What are organic factors

Vitamins, amino acids, purines and pyrimidines that cannot be synthesised by themselves and are obtained from the environment

Biofilms

Microbial communities attached to a surface and form slime or hydrogels. Communicate through quorum sensing

What criteria is important for growing microorganisms

• correct nutrients for growth

• Sufficient moisture

• Adjusted pH

• Suitable level of O2

• Sterile

• Incubated in correct temp conditions

Culture medium

Nutrients prepared for microbial growth in the lab

Sterile

No living microbes

Inoculum

Introduction of microbes into medium

Culture

Microbes growing in/on culture medium

Agar

Complex polysaccharide that is used as a solidifying agent for culture media

What temperature does the agar solidify

40

What temperature does agar liquify

100

Chemically defined media

Exact chemical composition is known

Complex media

Slightly varies per batch, extracts and digests of yeasts, meat or plants

Anaerobic culture methods

Contain chemicals that combine oxygen then use heat to drive off oxygen

Special Culture techniques

Some bacteria will not grow in culture and can only grow inside cells

Capnophiles

Microbes that grow better at high CO2 concentrations

Differential media

Distinguishes colonies

Enrichment media

Favours growth of desired microbes

Selective media

Encourage desired microbes to grow and suppress unwanted microbes

Pure cultures

Contains only one species or strain of bacteria

Colony

A population of cells that arise from a single cell or spore or from a group of attached cells called a colony-forming unit

What is this method called

Streak plate method

Types of preserving bacterial cultures for a long term

• deep-freezing

• Lyphilization, freeze-dying,

Name the growth phases of bacteria

1. Lag phase

2. Log phase

3. Stationary phase

4. Death phase

Lag phase

Intense activity for preparing for population growth, but no increase in population

Log phase

Logarithmic or exponential, increase in population

Stationary phase

Period of equilibrium, microbial deaths balance production of new cells

Death phase

Population is decreasing at a logarithmic rate

What are the direct methods to measure microbial growth

• plate counts

• Filtration

• Direct microscopic count

• MPN

What are indirect methods used to measure the microbial growth

• turbidity

• Metabolic activity in

• Dry weight

What are the advantages and disadvantages of plate counts

• A: count viable cells

• D: can take a long time, cells can form clumps

How do you calculate the number of bacteria on a plate count

Number of colonies on plate * reciprocal of dilution of sample = number of bacteria/ml

Advantages and disadvantages of direct microscopic count method

• A: no incubation required

• D: count dead cells, motile bacteria is difficult to count, need high concentration of cells

Turbidity

Measurement of cloudiness with spectrophotometer

Metabolic activity

Amount of metabolic product is proportional to the number of bacteria

Dry weight

Bacteria are filtered, dried and weighed then used for filamentous organisms