Microbial Growth Flashcards
Binary fission
Bacterial Cell Replication.
Process:
1) bacterium cell copies it’s DNA, at the origin of replication.
2) cell elongation occurs and doubles its cellular components.
3) cellular components move to opposite sides of the cell and cleavage furrow begins to form for the division.
4) formation of division septum occurs and constricts.
5) two daughter cells (complete copies) are created.
Cytokinesis
Division of the cytoplasm producing two distinct cells.
Ftsz
A protein that directs cytokineses by forming a Z ring on the cytoplasmic membrane. Z-ring is anchored by Ftsz binding proteins and defines the division plane between the daughter cells.
Generation Time
In prokaryotes this is the doubling time, or the times it takes for the population to double through one round of binary fission. (Varies in species)
Equation: Nn=No2^n
Nn=#of cells at any generation n
No=initial # of cells
n= # of generations
Growth Curve
Reproducible growth pattern of microorganisms grown in closed culture, where no nutrients are added and waste isn’t removed.
Culture Density
The number of cells per unit volume plotted in growth curve.
Lag Phase
Beginning of the growth curve. Represents a small number of cells referred to as “inocolum” that are added to a fresh culture medium.
Number of cells do not change during this phase but cells grow larger and are metabolically active, synthesizing proteins needed to grow. If any damages, repair takes place at this time.
Log phase “exponential phase”
Cells actively divide via binary fission and numbers increase exponentially (between time and number of cells instead of linear, but appears linear).
This phase shows constant growth and uniform metabolic activity, which is preferred for research work and industrial applications.
Also most susceptible to action of disinfectant and antibiotics at this time, that affect protein, DNA, and cell wall synthesis.
Generation time is genetically measured by intrinsic growth rate.
Stationary Phase
The total number of live cells reaching a plateau. (D/t waste accumulation, nutrient loss, oxygen depletion).
Here the number of cells created are = to the number of cells dying. Population is stagnant and culture density is constant.
Less susceptible to antibiotics d/t slow growth of everything.
Some cells undergo Sporulation if can produce endospores.
Death phase
Cells die in greater numbers, which exceeds living cells. Leads to exponential decrease in number of cells.
Cells lyse, releasing nutrients to allow other cells to survive and maintain viability to form endospores.
“Persisters” have a slow metabolic rate, and are medically important because they associate with certain chronic infections that do not respond to Tx.
Chemostat
Can be used to maintain logarithmic phase “exponential growth phase”.
A culture vessel with a opening to add nutrients and a outlet to remove waste and dead cells.
If aerobic then suitable oxygen levels are maintained.
Bacterial Count
Used to estimate the number of bacterial cells in a sample.
Clinically serves as indication of the extent of a infection.
I’m quality control used to detect contamination and prevent spread of disease.
Two methods used: direct and indirect cell count
Direct Cell Count
Refers to counting cells in a liquid culture or colonies on a plate.
Methods:
1) counting chambers: transfer bacteria to a calibrated slide (Petroff-Hausser chamber) and count cells under light microscope.
2) Electronics cell counting device (flow cytometry/coulter counter)detect and count the changes in electrical resistance in saline solution.
3) membrane filters: filter water sample, place filter on agar plate, incubate, count colonies.
Plate Count
A count of viable cells. Viable cells replicate and give rise to visible colonies when intubated. A low estimate of active number of live cells.
2 methods: pour plate or spread plate.
Most probable number method (MPN)
Used when organisms in dilute sample are too low to be detected by plate count method.
Often used for food or water, evaluates detectable growth by observing change in turbidity or color due to metabolic activity.
Indirect Cell Counts
3 methods:
1) spectrophotometry (measure turbidity or cloudiness of a sample)
2) measuring dry weight (cell suspension used must be concentrated via filtration or centrifugation, washed, dried, measured)
3) metabolic activity
Fragmentation
Filamentous Cyanobacteria replicate via this method.
Many nucleotide accumulate in an enlarged round cell or along a filament, leading to generation of many new cells at once. New cells will often split from the parents filament and float away.
Budding
Several daughter cells grow fully in the parent cells, which eventually disintegrates, releasing new cells into the environment.
In other species it may form a long narrow extension at one pole. The tip of the extension swells and form a smaller cell, the bud then detaches.
(Example: Yeast)
Biofilm
A complex community of microorganisms attached to a surface. Any surface in a liquid environment with minimal nutrients can develop into a biofilm.
Biofilm Formation
Formation involves attachment of planktonic cells to a substrate, then become sessile.
1) reversible attachment of planktonic cells (seconds)
2) first colonies become irreversibly attached ( second to minutes)
3) growth and cell division (hours to days)
4) production of EPS (extracellular polymeric substances) and formation of water channels (hours to days)
5) attachment of secondary colonizers and dispersion of microbes to new sites (days to months)
Biofilm Characteristics
Biofilms related to human health
-plaque contribute to dental and periodontal disease
-form wounds that cause serious infection that spreads
-pseudomonas aeruginos colonized biofilms in airways of cystic fibrosis patients, causing fatal and chronic infection.
- form on medical devices causing infection (catheter)
-biofilms provide ideal environment for the exchange of extrachromosomal DNA, which often includes genes that confer antibiotic resistance.
Quorum Sensing
Mechanism in which cells in a biofilms coordinate activities in response to environmental stimuli. (Occurs in cells in different species within a biofilm)
Enables microorganisms to detect their cell density through release of binding if small, diffusible molecules “auto inducers”.
When populations reach critical threshold (quorum) auto inducers initiate a cascade of reactions that activate genes associated with cellular functions that are beneficial only when the populations reaches critical density.
Obligate (strict) aerobes
Can not grow w/o abundant O2 supply.
Obligate Anaerobes
Killed by O2 (C. Diff).
Facultative Anaerobes
Thrive in presence of O2 but also grow in it’s absence by replying on fermentation or anaerobic respiration, if there’s a suitable electron acceptor other than O2. ( staphylococcus).
Aerotolerant Anaerobes
Indifferent to presence of O2. Does not use because they usually have a fermentation metabolism, but aren’t harmed in present of O2 (lactobacilli and streptococci).
Microaerophiles
Bacteria that require minimum level of O2 for growth, 1-10% well below the 21% found in the atmosphere (campylobacter Jejuni).
Why is it important for prokaryotes to regulate their pH and how do they do this?
Extreme pH affects the structure of all macromolecules. The H+ bonds holding together strands of DNA break up at high pH.
Important for preservation of food and microorganisms survival in stomach.
