Exam 2 Measuring microbial growth 9/26 Flashcards
Direct cell count
count all cells present; automated or manual
Indirect Measurements of Cell Mass
dry weight
- time consuming and not very sensitive
quantity of a particular cell constituent
- e.g., protein, DNA, ATP, or chlorophyll
dipstick
Growth
growth refers to population growth rather than growth of individual cells
In laboratory studies, populations typically display a predictable pattern over time
this is a ____________
growth curve
What on a growth curve can determine how fast a bacteria is growing, or which is growing faster?
slope of growth curve
Lag phase
– “flat” period of adjustment, enlargement; little growth
cell synthesizing new components
e.g., to replenish spent materials
e.g., to adapt to new medium or other conditions
Exponential growth phase
– a period of maximum growth will continue as long as cells have adequate nutrients and a favorable environment, population is most uniform
Stationary phase
- rate of cell growth equals rate of cell death caused by depleted nutrients and O2, excretion of organic acids and pollutants
Death phase
– as limiting factors intensify, cells die exponentially
*never goes to 0
Stationary Phase and Starvation response is to Activate survival strategies which include
morphological changes
e.g., endospore formation
Decreasing in size
RpoS protein assists RNA polymerase in transcribing genes for starvation proteins
Death Phase 2 Processes
two alternative hypotheses
- cells are Viable But Not Culturable (VBNC)
- cells alive, but dormant, capable of new growth when conditions are right
programmed cell death
fraction of the population genetically programmed to die (commit suicide)
Balanced Growth
cellular constituents manufactured at constant rates relative to each other
Unbalanced Growth
rates of synthesis of cell components vary relative to each other
occurs under a variety of conditions
change in nutrient levels
shift-up (poor medium to rich medium)
shift-down (rich medium to poor medium)
Demonstrates that microbial growth is under precise, coordinated control and that organisms respond quickly to changes in environmental conditions.
Generation time
The time to double the population in the exponential phase
Growth rate
Number of generations/unit of time (inverse of the generation time)
