Bacterial Cell Division Flashcards
What is microbial growth?
Does NOT refer to cell size
Refers to the increase in number of cells in a population
What is binary fission?
cell dividing into two new cells
What is the process of binary fission?
Cell increases in size (about twice the size); genome is duplicating
Septum forms: a partition that constricts the cell into two daughter cells (about half-way)
–> Results from the inward growth of the cytoplasmic membrane and cell wall
Septum pinches off
How does the septum form?
Results from the inward growth of the cytoplasmic membrane and cell wall
What is the generation time?
time required for binary fission; time for a single cell to double
What is a generation?
occurs as one cell separates to form 2 cells; period between 1 cell and 2 cells
How variable is generation time?
Varies between organisms; within a single organism it can vary according to conditions (e.g. ideal/lab vs. normal growth conditions)
How is a populations size measured?
2^n where n=#generations
What are Fts proteins?
filamentous temperature sensitive
Essential for cell division
What happens in the case of mutations of Fts protein?
- Mutations on genes that encode for Fts proteins cause impaired cell division. Instead of normal division, the cells form long filamentous cells that fail to divide (septum doesn’t form)
Multiple copies of genome in the filamentous cells
When do the filamentous cells occur?
- Mutations of Fts
- Non-permissive temperatures for binary fission
What is the major Fts protein?
FtsZ: homologous to eukaryotic tubulin
What is the divisome?
- cell-division apparatus formed by Fts proteins
Forms between the duplicated nucleoids
Formation starts with the attachment of FtsZ molecules in a ring around the center of the cell
What triggers the formation of the divisome?
completion of DNA replication
How does the divisome disappear?
Cell wall and cytoplasmic membrane forms along the plane, breaking down the divisome
–> Formation of the septum
What are the limiting factors of microbial growth?
- Nutrient availability
- Formation of toxic metabolic wastes
What “shape” describes the microbial growth cycle?
Growth curve
What are the phases of the microbial growth cycle?
- lag phase
- log phase
- stationary phase
- death phase
Describe the 1st phase of the microbial growth cycle.
Time that immediately follows inoculation
Little to no growth
Time needed for nutrient replenishment
Cells are metabolically active at this time
Describe the 2nd phase of the microbial growth cycle.
Maximum growth rate: due to maximum metabolic rate
Cells are most sensitive to metabolic inhibition
Describe the 3rd phase of the microbial growth cycle.
No net increase or decrease of cells
This stage is due to either
o Depletion of essential nutrient (used up)
o Waste product accumulates in the medium and inhibits growth
Cells switch to a lower level of metabolism (less energy usage)
Switch in metabolic pathways
–> Produce secondary metabolites: pigments or antibiotics
Decreased sensitivity to metabolic inhibition
Describe the 4th phase of the microbial growth cycle.
Cell death is greater than cell division
What are the environmental conditions for microbial growths?
1) Temperature (most important!)
2) pH
3) Osmotic pressure
4) Oxygen availability
