Question

1. A bacterium is inoculated into a medium containing two carbon sources, one of which is the bacterium’s preferred carbon source. The resulting growth curve shows two lag phases. Explain this phenomenon. What is this type of growth called? Include a diagram of what the growth curve would look like and indicate the usage of each carbon source.

2. An experiment is performed in lab in which gene expression profiles are measured during different growth phases. Each growth phase had different gene expression profiles. Explain this result

Answer 1

Question 1:

This type of growth is called Diauxic or Diphasic growth and the growth curve from obtained is called is Diauxic or Diphasic growth curve. When the microorganism grow in a medium with two carbon substrate, it first utilises the preferred carbon source till it is exhausted – then it goes under a short lag phase, (the second lag phase) and then continues it lifecycle. Now the cause of the second lag phase is preparations undertaken by the microorganism to switch from its preferred carbon source to the available optional utilisable carbon source (like synthesising the required enzymes).

Question 2:

The gene expression (mRNA and Protein) profiles are measured during different growth phases and they will be different. Let’s take an example of glucose lactose utilization by E. coli.

When the bacterium is utilizing glucose, the lac operon is off – the transcription do not happen so no synthesis of the Lac operon proteins, so a profile in this time will show only the proteins and mRNA associated with the uptake and utilization of the Glucose, not of the Lac operon, but as soon as the bacterium switches from glucose to lactose, the Lac operon becomes active while the glucose operon is stopped. So a profile now will show the proteins and mRNA associated with the uptake and utilization of the Lactose, not of the glucose