Template:SBB-Protocols Assay3

Silver Biomineralization Assay

Here we present an assay to determine whether the AG4 Silver binding peptide is present in the outer membrane of E.coli.

Procedure

Experimental Group

Picking and Incubating Colonies

• Add 4mL of LB media with the appropriate antibiotics to a clean test tube
• Pick a well-isolated, round, and "normal" looking colony of our proposed silver binding peptide with a pipet tip
• Drop it in the test tube
• Incubate at 37 overnight

Cleaning

1. Pellet 1.5 mL of saturated culture by spinning full speed, 30 seconds.
2. Dump supernatant, repeat to pellet another 1.5 mL (for a total of 3 mL)
3. Pour out the supernatant (contains extracellular proteins, unneeded nutrients)
4. Add 200uL of PBS Buffer and resuspend
5. Centrifuge the colony solution for 30 seconds
6. Pour out the supernatant
7. Add 200uL of PBS Buffer and resuspend
8. Measure OD of solution using spectrophotometer (at 600nm)

Treating with Silver

1. Centrifuge the colony solution for 30 seconds
2. Pour out the supernatant (contains extracellular proteins, unneeded nutrients)
3. Add 200uL of 0.1 mM silver nitrate and resuspend the cells
4. Incubate overnight (24-48 hours) at room temperature
5. observe color change and precipitation of colored compound

Control Group - non-AG4 cells

Picking and Incubating Colonies

• Add 4mL of LB media with the appropriate antibiotics to a clean test tube
• Pick a well-isolated, round, and "normal" looking colony of control E coli with no silver binding peptide with a toothpick
• Drop it in the test tube
• Incubate at 37 overnight

Cleaning

1. Pellet 1.5 mL of saturated culture by spinning full speed, 30 seconds.
2. Dump supernatant, repeat to pellet another 1.5 mL (for a total of 3 mL)
3. Pour out the supernatant (contains extracellular proteins, unneeded nutrients)
4. Add 200uL of PBS Buffer and resuspend
5. Centrifuge the colony solution for 30 seconds
6. Pour out the supernatant
7. Add 200uL of PBS Buffer and resuspend
8. Measure OD of solution using spectrophotometer (at 600nm)

Treating with Silver

1. Centrifuge the colony solution for 30 seconds
2. Pour out the supernatant (contains extracellular proteins, unneeded nutrients)
3. Add 200uL of 0.1 mM silver nitrate and resuspend the cells
4. Incubate overnight (24-48 hours) at room temperature
5. observe color change and precipitation of colored compound

other controls

1. Chemically reduce silver nitrate to precipitate silver (tells us silver nitrate is precipitating)
2. Lyse cells over-expressing AG4 and run assay (tells us if AG4 is precipitating silver)
3. Wash non-AG4 cells with silver nitrate and look for colour change (tells us if precipitation occurs without AG4)