MICR-4120 Lecture Notes - Lecture 2: Absorbance, Hyphomicrobium, Cell Division
20 May 2019
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Cell division
1. Binary fission
a. One cell becomes two
2. Budding: hyphomicrobium
3. Transverse fission: caulobacter
a. Can synchronize cultures so that every cell is doing same step at same time
Turbidity
● Turbidity: particles in solution scatter when light is shone through
○ Quantification of light being scattered helps determine how many cells are in the
solution
● Optical density: use to measure turbidity and standardize experiments
● Absorbance: use to look at chemical properties of substance
Phases of growth
1. log/exponential (adaptation)
2. Stationary (diversity and recycle of nutrients)
3. Death (resource depletion)
a. Not a gradual decrease
b. Can be exponential super quickly
● Optical density does not distinguish b/w living and dead cells leading to a lack of death
phase
○ Viable cell count does do this
Changes during Growth Curve
● Lag phase: cells adjust physiology to conditions, optimizing gene expression and prepare
to divide
● Log phase: cells tend to get smaller as they reach genetic capacity
○ Better conditions lead to faster growth
● Stationary phase: cells express different gene systems based on residual nutrients
○ Size of cells increases along w internal cell signals
● Death phase: consumable resources are minimal and starvation occur
○ Membrane lipids change
○ Surface charges can change hydrophobicity of cell
■ Leads to the cell being in a viable but nonculturable state
○ Limiting in nutrients causes shift in gene expression patterns
○ Some cells become more resistant to environmental stressors
■ Ex. temp, pH, resistant oxygen species, and desiccation
○ Ribosomes inc/dec in number depending on growth rate
■ Increase ribosomes leading to growth fast
Stringent Response
