Lab 9 - Pollutant degrading bacteria

Question 1

What is the major limitation of the spread plate technique? What technique is used instead?

Answer 1

• If organism of interest is rare in sample eg 0.1% of population, it’s unlikely to form a colony
• Use enrichment culture to provide favourable growth conditions

Question 2

How does the enumeration technique, the most probable number (MPN), work?

Answer 2

1. Serial dilution until no growth; done in replicate
2. Pattern of growth compared to MPN index

Question 3

What is the main source of anthropogenic pollution of aquatic ecosystems?

Answer 3

Petroluem from chronic continuous low level inputs and major acute oil spills

Question 4

Which serial dilutions are selected to calculate the MPN?

Answer 4

• The 3 serial dilutions preceding the first set of triplicate wells with no turbidity/growth
• Count the number of wells with turbidity/growth for each dilution to get MPN code

Question 5

How do you calculate the MPN of organisms per mL in the original sample?

Answer 5

1. Select 3 serial dilutions before first triplicate with no turbidity
2. Count positive/turbid wells in selected 3 dilutions = 3 digit code
3. Obtain MPN value from given table and correct for DF

Question 6

Briefly describe the method used in this experiment

Answer 6

1. Serial dilute water sample in MBM+YE
2. Transfer dilutions to Nunc trays with MBM+YE added
3. Add oil to dilutions
4. Incubate 7 days at room temp
5. Observe for turbidity (growth)