characteristics and study of prokaryotic growth how do we grow bacteria in the laboratory? what is...
DESCRIPTION
Historically (19 th century): Koch’s postulates –applied to prove that a particular organism caused disease -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 animal? Koch proved that B.anthracis causes anthrax and that M. tuberculosis causes tuberculosis this way Koch also developed new methods for bacterial growthTRANSCRIPT
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?
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?
Historically (19th century):
Koch’s postulates –applied to prove that a particular organismcaused disease-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 secondanimal?
Koch proved that B.anthracis causes anthrax and thatM. tuberculosis causes tuberculosis this way
Koch also developed new methods for bacterial growth
What is required for pure culture?
Sterile apparatusAseptic techniqueAppropriate media
solid media: separable colonies
Bacteria “grow” (i.e, divide) by binary fission
With each generation the population doubles
“generation time,” or doubling time, varies withbacterium and growing conditions
Can be as little as 20 minutes
Thus bacterial contamination can be rapidly established
What sorts of factors affect bacterial growth?temperature
How can they grow at such a wide range of temperatures?
Implicationssubstances that function at extreme temperaturesfor prevention of contaminationfor pathogenesis(why do we develop fevers?)
Oxygen requirements
Availability varies in the environment and on/in our bodies
pH
Bacteria maintain an internal neutral pH, but may survivein a wide range of acidic or alkaline environments
How?H. pylori- produce urease; generates ammonia andraises pH of immediate environment
Other bacteria use proton pumpsacidophiles- outalkalophiles- in
Salt tolerance
Synthesize or pump solutes inside the cell (and drawwater)
Osmotolerant organism- can grow in dry environments(like skin)
Halophiles- require high salt conditions
High solutes concentrations are historically used topreserve foods
What do bacteria require to grow?
NutrientsEnergy sourceSome organisms require growth factors (fastidious)
Which is easiest to grow in the laboratory?
Some media are richer than others
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!
Adjusting atmospheric requirements
CO2 levels (capnophiles)
Candle jars (microaerophiles)
Anaerobe jars/chambers (guess)reducing agents
Why would you use selective enrichment medium?
Measuring bacterial growth
Considerations
RapidityViable vs. total bacteriaLarge numbers or small numbers of bacteria
Growth in progress?
Direct counting
RapidCan count organisms that can’t grow in medium
Can’t distinguish live from dead cellsMotile organisms are hard to count!
Special instruments needed
Viable counts
Of living (and growing) bacteriarequires some skill and time
Can be performed on special mediaNeed fairly concentrated culture
Dilute samplesmembrane filtrationMPN (most probable number)- statistical estimate,NOT direct count
Measuring cell mass
Most common method- turbidity (spectrophotometry)
Cells grown in liquid mediumCan measure “progress” of cell growth
Changes (in turbidity) correlate with increase in cell numbers
Growth can be measured either by turbidity or bycounting to determine growth curve
Metabolic activities change in late log/stationary phase
Metabolites are often of research/commercial interestBacteria can be grown to enhance production
How do bacteria actually grow in nature?
Are nutrients always available, and in constant amounts?
They may elaborate protective structures when necessaryglycocalyxendosporesbiofilm (protects communities of microbes)
Interactions may be required (one organism produces substances required by another