Ch. 5 Flashcards
Growth-
Increase in the number of cells
Binary fission-
Cell division following enlargement of a cell to twice its minimum size
Generation time-
Time required for microbial cells to double in number
During cell division, each daughter cell receives a chromosome and sufficient copies of all other cell constituents to exist as an ___ ___.
Independent cell
Most bacteria have shorter ___ ___ than eukaryotic microbes.
Generation times
___ ___ is dependent on growth medium and incubation conditions.
Generation time
Exponential growth-
Growth of a microbial population in which cell numbers double within a specific time interval
During ___ ___, the increase in cell number is initially slow but increases at a faster rate.
Exponential growth
Batch culture-
A closed-system microbial culture of fixed volume
Typical growth curve for population of cells grown in a closed system is characterized by four phases:
- lag phase
- exponential phase
- stationary phase
- death phase
Lag phase-
Interval between inoculation of a culture and beginning of growth
Exponential phase-
Cells in this phase are typically in the healthiest state
Stationary phase-
- growth rate of a population is zero
- either an essential nutrient is used up, or waste product of the organism accumulates in the medium
Death phase-
If incubation continues after cells reach stationary phase, the cells will eventually die
Continuous culture-
An open-system microbial culture of mixed volume
Chemostat-
Most common type of continuous culture device
Both growth rate and population density of culture can be controlled ___ and ___.
Independently and simultaneously
Dilution rate-
Rate at which fresh medium is pumped in and spent medium is pumped out
In a chemostat the growth rate is controlled by ___ ___.
Dilution rate
In a chemostat the growth yield is controlled by the concentration of the ___ ___.
Limiting nutrient
In a ___ ___, growth conditions are constantly changing; it is impossible to independently control both growth parameters.
Batch culture
___ ___ are sensitive to the dilution rate and limiting nutrient concentration.
Chemostat cultures
Chemostat cultures
At too high a dilution rate, the organism is..
Washed out
Chemostat cultures
At too low a dilution rate, the cells may..
Die from starvation
Chemostat cultures
Increasing concentration of a limiting nutrient results in..
Greater biomass but same growth rate
Microbial cells are enumerated by ___ ___.
Microscopic observations
Limitations of microscopic counts:
- cannot distinguish between live and dead cells without special stain
- small cells can be overlooked
- precision is difficult to achieve
- phase-contrast microscope required if a stain is not used
- cell suspensions of low density hard to count
- motile cells need to be immobilized
- debris in sample can be mistaken for cells
A second method for enumerating cells in liquid samples is use of a ___ ___.
Flow cytometer
Flow cytometer-
A second method for enumerating cells in liquid samples
A flow cytometer uses:
Laser beams, fluorescent dyes, and electronics
Viable cell counts (plate counts):
Measurement of living, reproducing population
Two main ways to perform plate counts:
- spread-plate method
- pour-plate method
The obtain the appropriate ___ ___, the sample to be counted should always be diluted.
Colony number
___ ___ can be highly unreliable when used to assess total cell numbers of natural samples.
Plate counts
The great plate anomaly-
Direct microscopic counts of natural samples reveal far more organisms than those recoverable on plates
Microscopic methods count ___ ___, whereas viable methods do not.
Dead cells
Different organisms may have vastly different requirements for ___.
Growth
Turbidity measurements-
- Indirect, rapid, and useful methods of measuring microbial growth
- quick and easy to perform
- typically do not require destruction or significant disturbance of sample
- sometimes problematic
Most often turbidity is measured with a ___.
Spectrophotometer
Most often turbidity is measured with a spectrophotometer, and measurement is referred to as ___ ___.
Optical density
To relate a direct cell count to a turbidity value, a ___ ___ must first be established.
Standard curve
___ is a major environment factor controlling microbial growth.
Temperature
Cardinal temperatures-
The minimum, optimum, and maximum temperatures at which an organism grows
Microorganisms can be classified into groups by their ___ ___ ___.
Growth temperature optima
Psychrophile-
Low temperature optima
Inhabit permanently cold environments
Mesophile-
Midrange temperature optima
Thermophile-
High temperature
Growth temperature optima between 45C and 80C
Hypertheromophile-
Very high temperature
Optima greater than 80C
Mesophiles are found in:
- warm-blooded animals
- terrestrial and aquatic environments
- temperate and tropical latitudes
