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Characteristics and study of prokaryotic growth How do we grow bacteria in the laboratory? What is required for growth? PowerPoint Presentation
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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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Presentation Transcript
slide1

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?

slide2

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?

slide3

Historically (19th 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 growth

slide4

What is required for pure culture?

Sterile apparatus

Aseptic technique

Appropriate media

solid media: separable colonies

slide5

Bacteria “grow” (i.e, divide) by binary fission

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

slide8

How can they grow at such a wide range of temperatures?

Implications

substances that function at extreme temperatures

for prevention of contamination

for pathogenesis

(why do we develop fevers?)

slide9

Oxygen requirements

Availability varies in the environment and on/in our bodies

slide10

pH

Bacteria maintain an internal neutral pH, but may survive

in a wide range of acidic or alkaline environments

How?

H. pylori- produce urease; generates ammonia and

raises pH of immediate environment

Other bacteria use proton pumps

acidophiles- out

alkalophiles- in

slide11

Salt tolerance

Synthesize or pump solutes inside the cell (and draw

water)

Osmotolerant organism- can grow in dry environments

(like skin)

Halophiles- require high salt conditions

High solutes concentrations are historically used to

preserve foods

slide12

What do bacteria require to grow?

Nutrients

Energy source

Some organisms require growth factors (fastidious)

Which is easiest to grow in the laboratory?

slide14

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!

slide17

Adjusting atmospheric requirements

CO2 levels (capnophiles)

Candle jars (microaerophiles)

Anaerobe jars/chambers (guess)

reducing agents

slide19

Measuring bacterial growth

Considerations

Rapidity

Viable vs. total bacteria

Large numbers or small numbers of bacteria

Growth in progress?

slide20

Direct counting

Rapid

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

slide21

Viable counts

Of living (and growing) bacteria

requires some skill and time

Can be performed on special media

Need fairly concentrated culture

Dilute samples

membrane filtration

MPN (most probable number)- statistical estimate,

NOT direct count

slide25

Measuring cell mass

Most common method- turbidity (spectrophotometry)

Cells grown in liquid medium

Can measure “progress” of cell growth

Changes (in turbidity) correlate with increase in cell

numbers

Growth can be measured either by turbidity or by

counting to determine growth curve

slide27

Metabolites are often of research/commercial interest

Bacteria can be grown to enhance production

slide28

How do bacteria actually grow in nature?

Are nutrients always available, and in constant amounts?

They may elaborate protective structures when necessary

glycocalyx

endospores

biofilm (protects communities of microbes)

Interactions may be required (one organism produces

substances required by another