Microbial Growth Flashcards
(49 cards)
What is the definition of growth?
It is an increase in cellular components that leads to a rise in cell numbers. (Increase in the number of organisms)
How do bacteria and archaea (haploid cells) reproduce?
Binary fission.
Define binary fission, give a concise explanation.
A mother cell replicates her nuclear material, forms a septum in the center of the cell, and creates two fully functioning, membrane enclosed, identical daughter cells, each with their own genetic material.
Define budding.
Budding is when bacteria and yeast reproduce by forming a growth at the end of their prostheca (cytoplasmic extrusion from cell).
Define multiple fission.
When one parent cell divides to form a basal cell and a larger apical cell (all contained within the cell membrane). The apical cell then undergoes multiple rounds of division, forming many daughter cells called Baeocytes, which are held within the cell wall of the parent until they are released.
Explain the form of reproduction that is known as multinucleoid filaments.
Occurs when a spore forms outgrowths, namely vegetative hypha, which continue to grow and form branches, and then an aerial hypha, which elongates and grows into many separate spores.
Name the similarities found in the reproductive systems of bacteria and archaea.
1) The genome of the cell must be replicated and segregated to form
distinct nucleoids.
2) At some point during reproduction each nucleoid becomes enclosed
within its own plasma membrane and eventually its own cell wall.
Which cytoskeletal protein (similar to actin in eukaryotes) is said to be involved in the replication of rod-shaped organisms? How does it work>
Murein cluster B (MreB). This protein polymerizes to form a spiral around the inside periphery of the cell. It is thought that the origin of each new replicated chromosome may arise from/ be associated with MreB. Maybe each chromosome moves to opposite poles of the cell by following the helical MreB tracks.
Does plasmid replication depend on chromosome replication?
No, plasmids are extra-chromosomal structures that replicate independently of the chromosomes.
How do plasmids replicate independently from the chromosomes?
Each plasmid bears genes that encode proteins responsible for their
segregation to each daughter cell.
E.g. E. coli has Plasmid R1 which produces 3 different proteins for replication:
1) ParM = actin homologue which poylmerizes to form long filaments in the cell (ATP dependent)
2) ParR and ParC = DNA binding proteins which bind to the origin of replication and link ParM to the plasmid.
Once all 3 proteins are attached, ParM elongated, moving each plasmid to opposite ends of the cell.
Septation definition.
The process of forming a cross wall between two daughter cells.
Cytokinesis definition.
The cytoplasmic division of a cell at the end of mitosis or meiosis, bringing about the separation into two daughter cells.
Steps in cytokinesis.
1) The cell selects a specific site at which the septum will form.
2) The Z ring will assemble.
3) The Z ring will link to the plasma membrane and the components of the cell wall (aided by anchoring proteins).
4) The machinery for cell wall synthesis assemble.
5) The cell begins to constrict (Z ring is constricting) and a septum forms.
Which protein forms the Z ring? How does is assemble?
FtsZ protein AKA tubulin homologue. FtsZ polymerizes to form filaments = meshwork that creates the Z ring.
How do the Min C,D & E proteins in E. coli ensure that the Z ring forms in the center of the cell?
Min C, D & E proteins oscillate between the two poles in the cell, forcing FtsZ to formulate the Z ring in the center of the cell, as the concentrations of the other proteins is too high at the poles.
Explain peptidoglycan formation.
Look at diagram and explain.
Explain microorganism growth during the Lag phase.
- Often followed by the inoculation of cells into a fresh medium.
- No/very little cell division
- Cells that are older/more stressed will take longer to acclimatize
- Essential enzymes and cofactors need to be made in order to facilitate cell growth
- Length of this phase depends on the environment and the type of bacteria
Explain microorganism growth during the Exponential/Log phase.
- The maximal rate of exponential growth
- The amount of growth is entirely dependent upon the genetic potential of the bacteria, their ability to adapt and the suitability of the environment (temp, pH).
- Growth occurs via BINARY FISSION, and the metabolic activity peaks during this phase.
- Microorgs. divide independently, so the growth is balanced/steady.
- Population is doubling in regular intervals.
Define the doubling/generation time for bacteria.
It is the time taken by one individual bacterium to divide.
Why would you observe a shift up in the exponential curve? (Unbalanced growth)
When cells are placed from an nutritionally poor medium to a medium that is nutritionally rich. These cells will enter a lag phase before beginning their exponential growth curve in order to create necessary machinery for cell reproduction (ribosomes).
Why would you observe a shift down in the exponential curve? (Unbalanced growth)
When cells are placed from a nutritionally rich medium to a medium that is nutritionally poor. The cells will enter a lag phase in which they will produce enzymes necessary for the biosynthesis of essential, unavailable nutrients.
Explain microorganism growth during the Stationery phase.
- The population growth stops and the growth curve is horizontal.
- Usually reached when bacterial no.’s reach 10^9 cells/mL in lot culture.
- Cells are not replicating, but remain metabolically active.
- This is caused by oxygen and nutrient limitations, as well as the accumulation of toxic compounds.
- Bacterial cells are beginning to experience starvation and may exhibit morphological changes and produce starvation proteins.
Explain microorganism growth during the Death phase.
- Usually logarithmic = a constant proportion of cells will die per hour.
- Caused by detrimental environmental changes e.g. nutrient loss or build up of toxic waste
- This leads to the decline in the number of viable cells
- Some cells can sacrifice (genetically programmed death) themselves in order to produce nutrients for the rest of the population.
- Genetically programmed sterility makes cellsVIABLE BUT NOT CULTURABLE (VBNC)
Equation to determine the mean growth rate constant (k).
k = logNt - logNo / 0.301t (generations/hour)
