Question

1. Table below shows the results from a transduction experiment. Calculate the number of transductants that has resulted from this experiment (show your calculations).

List 3 reasons for the bacterial growth on the control plates.

Culture	Transduction Minimal Medium
E.coli control 1	5
E.coli control 2	3
E.coli + P-22 plate 1	37
E.coli + P-22 plate 2	41

Answer 1

Part I : Calculate the number of transductants arising from the transduction experiment

Transductant = The E. coli cells that have taken up phage DNA

E. coli + P22 Plate 1 = 37 colonies

E. coli + P22 Plate 2 = 41 colonies

Considering both the plates were inocluted with same volume / dilution of transducted sample, the average colony (transductant) count can be determined:

Effective transductants = No. of E. coli + P-22 colonies - Control plate's colonies

= (37 + 41) - (5+3)

= 78 - 8

=70

Average number of transductants = Effective transductants / no. of tranduction plates

= 70/2 = 35 transductant colonies

#Total number of transductants in the sample cannot be calculated since the values for inculated sample, total volume etc are not provided.

The three possible reasons for growth on control plates:

1. Presence of contaminants on the stock of E. coli cells.

2. Failure to maintain complete aseptic environment while performing the experiment. There could be multiple instances such as media not properly autoclaved, laminar air flow malfunctioning, unsterilized pipettes/plates/spreader etc.

3. No form of selection pressure was employed such as antibiotic selection.