6.1-6.12: Measuring growth in the lab

Bacterial “growth”

Measured as increasing number of cells in a population

How do most bacteria reproduce?

Binary fission

• one parent cell divides and forms two offspring or daughter cells

Bacterial cell division steps

1) DNA replication

2) Protein synthesis and expansion of cytoplasm (cell elongates)

3) Septum forms and cell divides

How do Eukaryotic cells typically divide?

Mitosis

Binary fission is ______ growth

Exponential

• 2-4-7-16-32-64…

Generation (doubling) time

Time it takes for the population to double/ time it takes cell to complete one round of division

Bacteria will divide at a constant time interval, assuming what?

Abundance of resources

Bacterial Growth phases

1) Lag phase

2) Log phase

3) Stationary Phase

4) Death phase

1) lag phase

Bacteria are preparing their cell machinery for growth

2) Log phase

Growth approximates an exponential curve

• straight line, on a logarithmic scale

3) Stationary phase

Cells stop growing and shut down their growth machinery while turning no stress responses to help retain viability

4) death phase

Cells behind to die at an exponential rate

Pimrary metabolites

Produced during very active growth and metabolism

• ex/ amino acids, ethanol, citric acid, etc

• Log/Exp phase

Secondary metabolites

Not essential for rapid growth; often made for defense or survival

• e.g. antibiotics, toxins

• Stationary phase

Continuous culture- prolonging log phase example

Chemostat

• continuously adds fresh nutrient while removing spent culture at the exact same rate

• keeps volume and growth conditions constant

Direct measuring growth in the lab

1) Microscope count

2) Cell-counting intstruments

Indirect measuring growth in the lab

Measuring biomass

• turbidity or dry weight

Limitations with direction measuring directly

Plate counts- CFUs (colony forming-viable)

• doesn’t tell you if its alive or dead

Limitations with indirection measuring?

1) Serial dilution and plate counts

• multiple cells can form 1 colony

2) Filtration and plate counts

• counting CFU not individual cells

3) Metabolic activity- viable cells

• Estimates growth by measuring ATP or Co2