Question

1. What is the unique about the appearance of growth of S. marcescens at the different temperatures?
2. Why will a bacterium not grow at temperatures below its minimum temperature for growth? Why won’t it grow at temperatures above its maximum temperature for growth?
3. For S. marcescens, what would happen if you moved the tubes incubated at 4 Celsius to 23 Celsius? Why? What would happen if you moved the tube incubated at 55 Celsius to 23 Celsius? Why?

Answer 1

Answer 1. S. marcescens prodeuces pigments in response to particular temperature stimuli. This color change is clearly linked to changes in the environmental conditions, as the cells alter their metabolic strategy depending on the availability of oxygen.

S. marcescens produces a red pigment when grown at temperatures below 35-37C, but does not produce this pigment at higher temperatures, and give a pale off-white color. The intensity of this pigment per cell is greater when the bacteria are grown at higher densities, and growth in nutrient-poor media reduces the intensity, regardless of population density. The optimal growth range for S. marcescens is 25-37C, because above this temperature range pigment production ceases and loss of pigment might be associated with mild temperature stress.

Answer 2. Because growth of bacteria is because of metabolic activity dependent on the enzyme action. Generally, an increase in temperature will increase enzyme activity. But if temperatures get too high, enzyme activity will diminish because the protein (which is enzyme) will denature. On the other hand, lowering temperature will decrease enzyme activity. And at freezing temperature enzyme activity can fully stop. Prolong freezing cycle can denature the protein, apart from this freezing can cause water to expand and also make ice crystal lead to cell rupture.

Answer 3. At 23 degree Celsius it will give bright light pigment. Because it is near the most suitable growth temperature.

Moving from 55 to 23 they will give pale white color near at 37 degree Celsius.