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Characteristics and study of prokaryotic growth How do we grow bacteria in the laboratory? What is required for growth? How do we measure bacterial growth? What do bacteria do while they are growing? How do bacteria grow in the environment?. What is a pure culture?
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How do we grow bacteria in the laboratory?
What is required for growth?
How do we measure bacterial growth?
What do bacteria do while they are growing?
How do bacteria grow in the environment?
All of the organisms are descended from a single cell
(and therefore are identical)
Bacteria do not grow that way naturally
Most bacteria cannot be cultured that way
So why do it?
Koch’s postulates –applied to prove that a particular organism
-isolate organism from diseased animal
-establish a pure culture of the organism (and prove it)
- infect another animal with cultured bacteria
does this animal get sick?
are the same microbes isolated from the second
Koch proved that B.anthracis causes anthrax and that
M. tuberculosis causes tuberculosis this way
Koch also developed new methods for bacterial growth
solid media: separable colonies
With each generation the population doubles
“generation time,” or doubling time, varies with
bacterium and growing conditions
Can be as little as 20 minutes
Thus bacterial contamination can be rapidly established
substances that function at extreme temperatures
for prevention of contamination
(why do we develop fevers?)
Availability varies in the environment and on/in our bodies
Bacteria maintain an internal neutral pH, but may survive
in a wide range of acidic or alkaline environments
H. pylori- produce urease; generates ammonia and
raises pH of immediate environment
Other bacteria use proton pumps
Synthesize or pump solutes inside the cell (and draw
Osmotolerant organism- can grow in dry environments
Halophiles- require high salt conditions
High solutes concentrations are historically used to
Some organisms require growth factors (fastidious)
Which is easiest to grow in the laboratory?
Some are used to look at mixed cultures of microorganisms
Selective- allow some organisms to grow but not others
Differential- bacteria have different characteristics
Some are both!
CO2 levels (capnophiles)
Candle jars (microaerophiles)
Anaerobe jars/chambers (guess)
Viable vs. total bacteria
Large numbers or small numbers of bacteria
Growth in progress?
Can count organisms that can’t grow in medium
Can’t distinguish live from dead cells
Motile organisms are hard to count!
Special instruments needed
Of living (and growing) bacteria
requires some skill and time
Can be performed on special media
Need fairly concentrated culture
MPN (most probable number)- statistical estimate,
NOT direct count
Most common method- turbidity (spectrophotometry)
Cells grown in liquid medium
Can measure “progress” of cell growth
Changes (in turbidity) correlate with increase in cell
Growth can be measured either by turbidity or by
counting to determine growth curve
Bacteria can be grown to enhance production
Are nutrients always available, and in constant amounts?
They may elaborate protective structures when necessary
biofilm (protects communities of microbes)
Interactions may be required (one organism produces
substances required by another