Lecture Set 3 : Part 3 Flashcards
how is growth described in microbiology?
-an increase in the number of cells
-NOT an increase in size
what is binary fission?
-process of cell division following the enlargement of a cell to twice its minimum size
what are the basic steps to binary fission?
-cell elongation (duplication of cell contents) HAPPENS BEFORE BINARY FISSION
-septum formation
-completion of the septum, formation of walls, cell seperation
what can occur simultaneously for a cell?
-growth in cell size
-chromosome replication
-septum formation
what is generation time?
-denoted as g
-time required for the number of cells to double (complete binary fission)
-expressed in minutes or hours per generation
-also called doubling time
how do the cell constituents increase as a cell grows in size?
-increase proportionally for balanced growth
what type of pattern does binary fission lead to?
-pattern of exponential growth
-cell numbers will double at a constant and specific time interval (aka generation time)
-increase is slow initially, but increases at an ever faster rate (follows an exponential curve)
-slope of the curve increases continuously (not changing how fast binary fission is happening, increasing the cell numbers faster)
-can only be seen when plotted on a logarithmic scale (semi log)
what is the formula used to represent the relationship between the final cell number, initial cell number, and number of generations during a period of exponential growth?
-Nt = N0 * 2^n
-Nt = final cell number
-N0 = initial cell number
-n = # of generations during a period of exponential growth
what is growth rate?
-denoted as k
-the rate of increase in population number or biomass
-expressed as the number of doublings or generations per hour
what is the formula for growth rate?
-Log(Nt) - Log(N0) / Log(2)*delta t
-N0 = # of cells at time 1
-Nt = # of cells at time 2
-delta t = time 2 - time 1
what is the formula for generation time?
- 1/k
-k = growth rate
how do growth rates work for each different organism? what are some examples?
-each organism has a specific growth rate that is the fastest growth rate in optimal conditions (medium + temp + pH + incubation)
-ex: E.coli doubles every 20 minutes
-ex: Clostridium perfringens doubles every 10 minutes
-ex: Mycobacterium tuberculosis is a slow grower and doubles once every 24 hours
what is a batch culture?
-a closed system microbial culture of fixed volume
-closed system means nothing is added after inoculation and no wastes are removed
-fixed volume means it cannot grow indefinitely and is restricted to the resources and space given
what does the growth curve of a batch culture look like?
-characteristic growth curve that has 4 phases
what are the 4 phases of a batch culture growth curve?
-lag phase
-exponential (log)
-stationary
-decline (death)
what is the lag phase of a batch culture growth curve?
-period of time between inoculation of a culture and the beginning of growth (cell # increase)
-no growth takes place in this phase
-cells are adapting to the new medium and conditions (synthesize building blocks, make new enzymes, etc)
how is the length of the lag phase determined?
-depends on the culture and the conditions that the culture has been moved into
-if the new conditions have little difference from previous conditions = shorter
-if the new conditions have a large difference from previous conditions = longer
what occurs in the exponential (Log) phase of a batch culture growth curve?
-population exhibits exponential growth (linear portion of the curve, cells are synced)
-cells are healthy, actively growing, and of uniform composition
-portion used to calculate generation time
-used for further experiments because it limits experiment variation since cells are more uniform (called mid-log phase cultures)
what occurs in the stationary phase of a batch culture growth curve?
-cells are metabolically active but cell #’s stop increasing (growth and death rates are equal)
-typically occurs when an essential nutrient is used up or a waste product has accumulated in the medium
-phase where cells may undergo secondary metabolism
what is secondary metabolism?
-production of antibiotics, endospores, etc
what occurs in the decline (death) phase of a batch culture growth curve?
-if the incubation continues after cells have reached the stationary phase, cells will eventually die
-death rate is greater than growth rate
-cells can survive for many years in this phase
-not all bacteria will die (some may form endospores or other dormant cell types)
-rate at which cells die varies greatly between species
what are some other dormant cell types?
-akinetes (cyanobacteria + algae)
-cysts
what may some cells adopt in the death phase?
-a canniballistic lifestyle
-eat dead cells
-called cryptic growth
-form a subpopulation
how do the growth curves of viables counts/microscopic counts and optical density compare?
-for optical density measurements the lag phase looks above 0 because when cells are elongating they scatter more light (have not started growing)
-the rate is equal for either technique (good b/c OD is much quicker)
