Bacterial Transformation

AP Biology Transformation Lab

What is Transformation?

Changing the genes and phenotype of a bacteria by uptake of foreign/new DNA a natural process that bacteria have evolved in order to obtain DNA from

their environment. enables scientists to insert genes by recombinant techniques and place the

plasmid into a bacteria for expression

What is Transformation?

In order to transform bacteria we need to overcome two problems1. Disadvantage –cells that contain plasmids grow more slowly

There is pressure on cells to get rid of their plasmids Needs to be an Advantage to keep plasmids

Antibiotic resistance

2. How do we tell which cells have the plasmid? We use a marker

Grow the bacteria on plates that contain the antibiotic Use a color pigment marker that is present when a particular enzyme is present

Let’s review bacterial DNA first…

Let’s Review: Bacterial genome

Bacteria are prokaryotes—no nucleus. The area where DNA

is located is called the nucleoid

DNA is organized in one double stranded circular molecule

Bacterial DNA

Plasmid DNA

Bacterial cell

Genomic DNA

Size

Which bacteria will we be using?

Escherichia coli is the most common bacterium in the human gut. It has been extensively studied in the laboratory and is an important research organism for molecular biology.

E. coli reproduce very rapidly; a single microscopic cell can divide to form a visible colony with millions of cells overnight.

Like all bacteria, E. coli has no nuclear envelope surrounding the bacterial chromosome and thus no true nucleus.

All of the genes required for basic survival and reproduction are found in the single chromosome.

What is a Plasmid?

A circular piece of autonomously replicating DNA exists outside the main bacterial

chromosome Originally evolved by bacteria

Carries separate genes for specialized functions.

In genetic engineering, plasmids are one means used to introduce foreign genes into a bacterial cell.

Scanning electron micrograph

What is carried on the Plasmid?

The plasmid contains genes necessary for survival and can be passed from one bacteria to another

ampR gene confers resistance to the antibiotic ampicillin. E. coli cells containing this plasmid, can

survive and form colonies on LB agar that has been supplemented with ampicillin.

Cells lacking the ampR plasmid are sensitive to the antibiotic, which kills them.

An ampicillin-sensitive cell can be transformed to an ampicillin-resistant cell by its uptake of a foreign plasmid containing the ampR gene.

The same can be said for the lac gene, which codes for lactose. I

If this gene is taken in, the organism can break down lactose.

Transformation has 4 main steps

Prepare cells Make them competent

Incubate with plasmid Plasmid associates with membrane of cells

Shock the cells To initiate plasmid uptake

Allow cells to recover and plate on agar Allow cells to recover in rich medium for 0.5 – 1 h (without antibiotic

to avoid stressing the cells) Plate on agar with antibiotic for selection Next day can pick single colonies or clones

The Transformation Lab…

Our plasmid: pBlu plasmid

Into E. coli (scary?…no!)

Our plasmid contains genes for: AMP= ampicillin (an

antibiotic) resistance Beta-galactosidase-an

enzyme that converts X-Gal Indo Blu

Protein that allows for antibiotic resistance

Enzyme that breaks down X-Gal to make Indo Blu

RNA

RNA

How do we get the plasmid inside of the bacteria?

1. To transform cells, you first need to make them competent to take up extracellular DNA.

2. Obtain E. Coli bacteria cells + Add to ice cold CaCl2

1. Helps plasmid attach to bacteria

2. Makes the cell competent3. Add plasmid to same

microtube

1. E. Coli 2. pBlu plasmid

How It Works

Transformation solution CaCI2 Positive charge of Ca++ ions shields

negative charge of DNA phosphates

DNA becomes “neutral” and can pass through the cell membrane

Ca++

Ca++

OCH2

O

P O

O

OBase

CH2

O

P

O

O

O

Base

OH

Sugar

Sugar

OCa++

How do we get the plasmid inside the bacteria?

Wait…and then

Heat shock! This temporarily opens pores to allow the plasmid to enter the bacteria…timing is critical!!!

Chemical transformation

Ice-cold CaCl2

To make competent Slows the fluid cell

membrane Heat shock

Increases permeability of membranes by opening pores

Plasmid DNA is taken up

Nutrient broth incubation Allows beta-lactamase

expressionBeta lactamase(ampicillin resistance)

pBLU plasmids

Bacterial chromosomal DNA Cell wall

GFP

What is Nutrient Broth?

Luria-Bertani (LB) broth Medium that contains nutrients

for bacterial growth and gene expression Carbohydrates Amino acids Nucleotides Salts Vitamins

How will we know if the bacteria actually got into the plasmid?

Any ideas?

We can grow the bacteria on a plate: That contains ampicillin and X-Gal Regular bacterial medium

What do you predict will happen in each?

Predict

pBlu

pBlu

Control

Control

Amp

X-Gal

Regular

Amp

X-Gal

Regular

What will we observe???

Growing the bacteria

After they have received the plasmid…

Place on a growth media and allowed to grow.

~ 100 µlspread evenly

discrete colonies

(~106 cells)overnight37 ºC