Micro Exam 2 - Growth

What is growth?

population growth, not growth in size

Describe binary fission.

type of asexual reproduction in which bacteria replicates its DNA and divides in half, producing two identical daughter cells

What is FtsZ?

cell division protein that forms ring around center of cell, recruits cell wall synthesis machinery to build cell wall, related to tubulin

How does FtsZ recruit division machinery?

by polymerizing at new division site, recruiting other Fts cell division proteins, and PG synthesis machinery loads onto complex

What does Fts stand for and what does it mean?

filamentation temperature sensitive - cell division disabled at high temperatures

Where does FtsZ concentrate?

middle of cell

How does FtsZ find the middle of the cell?

the Min system

What does MinC do?

inhibit FtsZ rings

What does MinD do?

activate MinC and is a membrane bound anchor

Where are MinC and MinD localized?

poles

What is MinE?

topological determinant that forms a gap and controls where FtsZ can form

Where does MinE form?

at end of MinC shells which inhibits MinC

Describe how the Min system works.

MinC and MinD oscillate between poles because of MinD-GFP, MinE-GFP is constantly pushing shells out of the center by polymerization

What does nucleoid occlusion do?

prevent guillotining of chromosome in cell division

How does nucleoid occlusion work?

the Noc system

Describe the Noc system.

SlmA and Min system work together to prevent lethal guillotining - without MinC and MinD, cell division plane is random so SlmA prevents FtsZ from forming over chromosome, often making minicells

What is SlmA and what does it do?

synthetic lethal with Min that coats the chromosome and inhibits FtsZ from polymerizing over the chromosome

What are autolysins?

PG remodeling enzymes that break down PH to separate daughter cells

What are the four methods of measuring growth?

direct counting, viable counting, spectrophotometry, flow cytometry

What are the advantages to direct counting?

don't need to grow cells because you take an environmental sample, works for any sample

What are the disadvantages to direct counting?

cells must be evenly distributed, can't distinguish alive from dead

Describe viable counting.

spreading culture on petri plates and counting colony forming units (cfu)

What is the counting rule in viable counting?

What are the advantages of viable counting?

allows you to measure the number of viable cells, colony forming units (cfu) is a good standardization

What are the disadvantages of viable counting?

only works with culturable bacteria, assumes each colony originates from a single cell, problems with clumping, slow

How does spectrophotometry work?

it measures turbidity of culture, has to do with the idea that mass absorbs light - more dense culture = more light absorbed

In spectrophotometry, what readings are meaningful?

those between 0.1 (not dense) and 1.0 (quite dense)

What are the advantages of spectrophotometry?

most rapid technique (immediate), reliable and reproduceable

What are the disadvantages of spectrophotometry?

organism must be culturable, severe problems with clumping (underrepresents density), indirect measurement, changes in cell size can affect readings

What is flow cytometry?

counting individual cells with a laser, most modern technique, all other techniques combined

How does flow cytometry work?

bacteria flows through tube and are individually counted one at a time

What are the advantages of cytometry?

extremely accurate, can measure size

What are the disadvantages of cytometry?

slow, problems with clumping, can't differentiate between alive and dead cells

What is exponential growth?

growth pattern in which the individuals in a population reproduce at a constant rate

What does exponential look like on a linear and log scale?

linear - curved line, log - straight line

What is generation time?

the time it takes for a population to double

As growth rate increases, generation time _______________, and vice versa.

decreases

What are the two types of growth environements?

batch culture and continuous culture

Describe batch culture.

a finite amount of media is inoculated, starvation occurs because no nutrients enters the cell, is a closed system, no waste product leaves, is a poor model for the environment due to infections, continual flux, and waste products

What are the four stages of batch culture?

lag, exponential, stationary, death

Describe the lag phase.

slow or no growth, occurs after inoculation into fresh medium, either a period of physiological adjustment or an indicator of dead cells

Describe the exponential phase.

cell number doubles at regular intervals, metabolism of all cells is uniform

Describe the stationary phase.

no net increase in population size, cells have either stopped growing or died, growth rate is same as death rate, nutrient depletion or toxin accumulation

Describe the death phase.

population decreases, cells begin to lyse (cell membrane breaks down), death rate is greater than growth rate

Starvation is a ______________ response that occurs when...

stringent, amino acids run low

In starvation, what pauses due to a lack of amino acids?

translation

What is RelA?

a protein that binds to the ribosome and detects pausing, it synthesizes alarmone ppGpp

What is ppGpp?

single modified nucleotide that signals for starvation phase changes in physiology, a spot that increased on TLC plates after starvation

What are ghosts?

PG sacculi with stuff in them, when bacteria lose phase dark appearance, sure indicator of death

When is growth rate proportional to nutrient concentration?

only when nutrients are low, otherwise growth rate is constant

What is growth yield?

difference between starting and maximum cell numbers in the stationary phase

What is growth yield proportional to?

nutrient concentration

Describe continuous culture.

cells stay in exponential phase forever and never enter stationary phase, flow can be controlled, always in steady state

Continuous flow = ?

continuous growth

What is growth rate proportional to?

dilution rate

If dilution rate is greater than the generation time...

there will be a washout