9.1 how microbes grow

1st basic step of bacterial reproduction

Growth of cell size and increase in cell components

2nd basic step of bacterial reproduction

Replication of DNA

3rd basic step of bacterial reproduction

Division of the cytoplasm (cytokinesis)

4th basic step of bacterial reproduction

Septum formation and division of daughter cells

What directs cytokinesis in bacteria?

FtsZ protein

What does FtsZ assemble to form?

Z ring and divisome

What does the divisome activate the production of?

Peptidoglycan and septum

What is generation time?

Time taken to double population, doubling time

What is the generation time for E. coli?

20 minutes

What is the generation time for S. aureus?

30 minutes

What is the generation time for B. subtilis?

120 minutes

What is the generation time for M. tuberculosis?

15-20 hours

What type of growth is observed in populations with no resource constraints?

Exponential growth

Population size be predicted from any starting size T/F?

True

1 multiple choice option

Nn= N02^n

Calculating Population Size

What does N0 represent in population calculations?

initial number of cells

What does n represent in population calculations?

number of generations

How many generations occur in 8 hours if the generation time is 30 minutes?

16 generations in 8 hours

growth curve

Closed cultures have finite

resources (i.e. nutrients)

•Predictable pattern occurs

growth curve pattern

1. Lag phase

2.Log (exponential) phase

3.Stationary phase

4. death phase

lag phase

- cells adjust to culture medium;

no change in population

log phase

- binary fission occurs;

cell replication > cell death

stationary phase

resources become depleted; endospores can start forming

cell replication = cell death

death phase

- endospores persist cell replication < cell death

What characterizes open system cultures? (measuring growth)

They have infinite resources.

What resources are replenished in open system cultures?

Nutrients and air.

What happens to dead cells and waste in open system cultures?

They are removed (effluent).

Why are open system cultures beneficial?

They are beneficial for industrial microbiology.

quantifying populations:

size is important for determining infection, contamination of water or food supply, etc.

measuring growth methods

•Microscopic cell count

•Fluorescent staining for alive & dead cells

•Coulter count

•Viable cell count

•Optical Density

Microscopic cell count

Cells are counted under a microscope.

Calibrated slide

Known volume is transferred to a calibrated slide and cells are manually counted

Coulter counter limitation

Does not differentiate live/dead.

Microscopic cell count limitation

Cannot distinguish live vs. dead.

Coulter counter

Detects electrical resistance change due to cell density

Optical Density (turbidity)

Measured with spectrophotometer; light is passed through culture and measured on the other side

Population increase =

turbidity increase

Optical Density measurement

Includes dead & live cells

Fluorescence Staining

Cells are counted under a microscope or flow cytometer.

Red stain

Binds to damaged cells to indicate dead cells.

Viable cell count

Samples are diluted and grown on solid media; Limited only to easily cultured species

Colony forming units per volume (CFU/ml)

Results expressed in colony forming units per volume

Countable range for CFU/ml

Traditionally 30-300 CFU/ml (statistically most accurate).

<30 CFU/ml

TFTC (Too Few To Count).

>300 CFU/ml

TNTC (Too Numerous To Count).

What is required to count viable CFU?

Distinguishable and separate colonies.

What method is used to achieve the 30-300 CFU/ml range?

Serial dilution.

What scale is often used for dilutions in microbiology?

Log scale.

What is the purpose of the dilution factor?

To determine the original CFU count.

What is the Most Probable Number (MPN) method used for?

Statistical method used when counts are very low (<30 CFU/ml).

In which fields is the MPN method commonly used?

Water and food testing.

How many log dilutions are used in the MPN method?

3 log dilutions (e.g., 1/1, 1/10, 1/100).

What does the growth pattern in MPN indicate?

Growth is determined as positive or negative and compared to a reference table.

What are two methods of growth division in microorganisms?

Asymmetrical division (budding) and fragmentation.

fragmentation in ____

cyanobacteria

budding in _____

planctomycetes

What is a biofilm?

A micro ecosystem of one or more species that can provide protection.

In what environments do biofilms primarily form?

Mostly in liquid environments such as rivers, pipelines, and the oral cavity.

What is the 1st step in biofilm formation?

Attachment of planktonic cells to a substrate.

What happens after cells attach to a substrate in biofilm formation? (2nd step of bio form)

The attachment becomes irreversible, and cells become sessile.

3rd step of biofilm formation

What is produced during the growth and division of cells on a substrate? (4th step of bio form)

Extracellular polymeric substance (EPS).

5th step of biofilm formation

Attachment of secondary colonizers & dispersion of microbes to new locations

What role does quorum sensing play in biofilm formation?

It is a form of cell-to-cell communication that regulates biofilm development.

What are autoinducers in the context of biofilm formation?

Small molecules produced to induce various actions based on cell density or stress.

Classes: N-acylated homoserine lactones

(Gram =) Various short peptides (Gram +)

Name one beneficial aspect of biofilms.

Normal biota in the gut, which is beneficial for health.

What is a negative consequence of biofilm formation on teeth?

Plaque formation, which is harmful to dental health.

How do biofilms provide resistance to antibiotics?

Cells in deep layers may be metabolically inactive, EPS may slow diffusion of biocidal agents, and they provide an optimal environment for sharing plasmids.

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