Microbial Growth Flashcards
What is growth referring to in the case of bacteria?
Population growth.
What does growth result in an increase in?
Cellular constituents.
What are two possible results of an increase in cellular constituents?
- An increase in cell number.
- An increase in cell size.
What is a microbial growth curve?
A logarithmic curve that plots the observed growth pattern for microorganisms cultivated in batch culture.
*Has distinct phases.
What is the label for the X-AXIS of the microbial growth curve?
Time.
What is the label for the Y-AXIS of the microbial growth curve?
Number of cells.
What is the first phase on the microbial growth curve?
The lag phase.
What happens during the lag phase?
Synthesis of new components as the bacteria adapts to a new medium.
*May be absent if new medium is the same or similar to previous medium.
What is the second phase on the microbial growth curve?
The exponential/log phase.
What happens during the exponential phase?
The rate of division and growth is exponential.
*Population is most uniform.
What is the third phase of the microbial growth curve?
Stationary phase.
What happens during the stationary phase?
The reproductive rate and the death rate are balanced due to the threshold for total number of viable cells having been met.
What type of environment causes bacteria to enter the stationary phase?
- Nutrient limitation.
- Toxic waste accumulation.
- Limited oxygen availability.
- Critical population density reached.
What is the fourth phase of the microbial growth curve?
Death phase.
What happens during the death phase?
The number of viable cells exponentially declines at a constant rate due to environmental changes.
What are the two alternative hypotheses for what is happening during the death phase?
- Cells are viable, but not culturable (VBNC): Alive, but dormant and capable of new growth when conditions are right.
- Programmed cell death: Fraction of cell population is apoptotic at a certain threshold.
What is stage five of the microbial growth curve?
Long-term stationary phase.
What happens during the long-term stationary phase?
The bacterial population continues to evolve in waves of genetically distinct variants.
*Natural selection does occur.
What is quorum sensing?
A bacterial cell-to-cell communication process that involves the production, detection, and response to autoinducers (Ais).
Is quorum sensing density-independent or density dependent?
Density dependent.
What is the relationship between bacterial population and Ais?
Positive correlation.
What kinds of genes does quorum sensing control?
Genes that direct activities that are beneficial when performed by groups of bacteria acting in synchrony.
ex: Bioluminescence, sporulation, antibiotic production, biofilm formation.
What is it called when microbes grow attached to a surface?
Sessile.
What is it called when microbes are free floating?
Planktonic.
What are biofilms?
Complex, attached, slime-enclosed communities of microbes.
Where are biofilms ubiquitous?
Water, but can be formed on any surface.
What is the first step of biofilm formation?
Reversible attachment of planktonic cells. Still individual microbes.
*Planktonic step.
What is the second step of biofilm formation?
First colonizers become irreversibly attached.
*Attachment step.
What is the third step of biofilm formation?
Growth and cell division.
*Growth step.
What is the fourth step of biofilm formation?
Production of extracellular polymeric substance (EPS) and formation of water channels.
*Maturity step.
What is the fifth step of biofilm formation?
Attachment of secondary colonizers and dispersion of microbes to new sites.
*Dispersion step.
What does the EPS and changes in attached organisms’ physiology protect the bacteria from?
Harmful agents.
What makes a biofilm heterogeneous?
Differences in the metabolic activity and locations of the resident microbes. Additionally, exchanges between the resident microbes take place through metabolism, communication, and DNA uptake.
What does DNA uptake/transformation encourage?
Horizontal gene transfer.
