Imagine yourself as a plant pathologist. You are studying the effectiveness of t
ID: 256100 • Letter: I
Question
Imagine yourself as a plant pathologist. You are studying the effectiveness of the bacterium Pseudomonas fluorescens as a biocontrol agent against Phythium, which can cause “damping off” in seedlings. Now, answer the following questions:
1. You are planning a field experiment and need to harvest P. fluorescens cells from a batch culture when there are 1.68 x 108 cells/ml of culture medium. When should you be back in the lab if the flask currently contains 1.5 x 106 cells/ml? Assume that the generation time is 1.5hrs. Please show all of your work!
2. Harvested cells were then applied to the roots of cucumber seedlings at 107 cells/gram fresh root, then the seedlings were transplanted into the field. Two weeks later selected healthy plants were dug up, and the concentration of P. fluorescens on the roots was determined to be 104 cells/gram fresh root measured by plating onto nutrient agar. What could account for the loss in P. fluorescens?
Explanation / Answer
Please find the answers below:
Answer 1: The mathematical relation between the bacterial growth and the time can be found as below:
logNt = logNo + nlog2, where
Nt = Number of cells after the time
No = number of cells originally present
n = number of generations passed during time t,
thus, solving the equation as follows:
1.68*108 = 1.5*106 + nlog2
or n = logNt - logNo / log2
n = log1.68*108 - log1.5*106 / 0.301
n = 18.939 - 14.221 / 0.301
n = 15.67
Since generation time, g can be given as the ratio of time taken for achieving the population to Nt via time t, we can have,
g = t/n,
thus, t = g*n or 1.5 * 15.67 = 23.5 h
Thus, the experimenter can return after nearly 24 h for conducting the experiment while the required growth number will be achieved in the culture.
Answer 2: According to the information, fresh seedlings were transplanted into the field with a high count of P. fluorescence but the density of bacteria decreased with a span of two weeks by 1000-fold. The possible reason s behind this observation can be as enlisted below:
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