Module 3 Flashcards
Describe the prokaryotic process of prokaryotic process of binary fission
Look in text book.
What eukaryotic cellular process is most similar to prokaryotic binary fission
Mitosis
In microbial growth what does “doubling time” mean?
The time it takes for the population to double through one round of binary fission
How are the number of cells in a culture and the generation number related?
Nn is the number of cells at any generation n, N0 is the initial number of cells, and n is the number of generations.
How do you calculate the population size in a culture at a given time when you know the doubling time? (assuming no cell death)
2^n, where n is the number of generations
Lag phase
- No increase in number of living bacterial cells.
- Small number of cells (innoculum) added to culture medium
- Cells gearing up for next phase of growth
- Number of cells does not change
- Cells grow larger
- Cells are metabolically active, synthesizing proteins needed to grow within the medium
- If any cells damaged or shocked, repair takes place here
- Duration of lag phase determined by species, genetic make-up, composition of medium, size of original inoculum
Log phase
- Exponential increase in number of living bacterial cells
- Cells actively dividing by binary fission
- Generation time under specific growth conditions genetically determined
- Generation time referred to as intrinsic growth rate
- Relationship between time and number of cells is not linear, but exponential, but growth curve plotted on semilogarithmic graph which gives appearance of linear relationship.
-Waste products accumulate, nutrients used up, depletion of oxygen limit aerobic cell growth, which stall population growth
Stationary phase
- Plateau in number of living bacterial cells; rate of cell division and death roughly equal
- Population of living cells relatively stagnant
- Culture density and stationary culture constant
- Cultures carrying capacity or maximum culture density depends on the types of microorganisms and specific conditions of culutre
-carrying capacity is constant for a given organism grown under the same conditions. - Cells switch to survival mode of metabolism
- Growth slows so does synthesis of peptidoglycans, proteins, nucleic acids, less susceptible to antibiotics that disrupt these processes.
-In bacteria capable of producing endospores, many cells undergo sporulation during the stationary phase.
Death phase
- Exponential decrease in number of living bacterial cells
- Culture medium accumulates toxic waste and nutrients are exhausted, cells die in greater and greater numbers.
- Number of dying cells exceeds number of dividing cells
- Cells lyse and release nutrients into medium allowing surviving cells to maintain viability and form endospores.
Why is the standard growth curve observed only in closed cultures (i.e.
nothing is added or removed after inoculation)? How is a chemostat
different?
Bacteria will grow in a predictable pattern in closed cultures (growth curve). A chemostat is used to maintain a continuous culture in which nutrients are supplied at a steady rate. Bacterial suspension is removed at the same rate as nutrients flow in to maintain an optimal growth environment.
What is the difference between direct and indirect methods of quantifying growth
- Direct cell count refers to counting the cells in a liquid culture or colonies on a plate. Ex. Direct microscope cell count
- Indirect cell counts are an indirect detection of cell density and are commonly used to estimate and compare cell densities in a culture. Ex. Turbidity (cloudiness) of a sample of bacteria in a liquid suspension using spectrophometer
What is a biofilm?
Complex and dynamic ecosystems that form on a variety of environmental surfaces.
What is the same in all environments where biofilms occur?
Regardless of the environment where they occur, biofilms are not random collections of microorganisms; rather, they are highly structured communities that provide a selective advantage to their constituent microorganisms.
Explain in simple terms how a biofilm forms on a surface
- Reversible attachment of planktonic cells
- First colonizers become irreversible attached.
- Growth and cell division
- Production of EPS and formation of water channels
- Attachment of secondary colonizers and dispersion of microbes to new sites.
- Involves the attachment of planktonic cells to a substrate, where they become sessile (attached to a surface).
Obligate anaerode
Are killed by oxygen
aerotolerant
Indifferent to the presence of oxygen, do not use oxygen because they have fermentative metabolism, but are not harmed by oxygen.
microaerophile
Require minimum level of oxygen for growth (1-10%)
facultative anaerobe
Thrive in the presence of oxygen, but also grow in its absence by relying on fermentation or anaerobic respiration
obligate aerobe
Cannot grow without an abundant supply of oxygen