Cells (in our case E. coli) are delicate and require a great deal of attention to detail for them to grow well. A slight change to their surroundings can vastly affect their ability to reproduce and generate products.

Oxygen is required for most microbes to live and grow, however if in excess, it is toxic! The high oxygen generates free radicals, high levels of free radicals affects their cell growth and may even kill them. However oxygen also has a low solubility in water which makes it necessary for us to introduce methods which will allow for enough oxygen to dissolve and meet the cell oxygen demand.

For most cells, the optimal pH is around 6.5 to 7.0, any more or less then that places stress on the cells.

Lastly, temperature is best maintained around 37 degrees Celsius as most cells grow best. Anything above a temperature of 40˚C will affect the cells, and most likely killing them since proteins will be denatured in high temperature. It is also important that the fluctuations in the temperature are kept to a minimal as a constantly changing environment is defiantly stressful for us, much more so for cells.

2. Describe the principle of the spectrophotometer which was used to determine the cell density (OD600). Why was 600nm used?

A spectrophotometer works by measuring the amout of light, sent out by a light source, received by the detector. The light source sends out light which are split up by a prism into various bands of differing wavelengths. An appropriate slit or device then allows the specific band of wavelength through and shines it on the sample or blank.