When the bacterium Serratia marcescens is grown on a sterile culture medium in a petri dish at 30°C, the bacterial colonies are cream colored. When this same bacterium is cultured under identical conditions, except at a temperature of 25°C, the colonies are brick red. This difference in color is most likely due to the
1
type of nutrients in the culture medium
2
sterilization of the culture medium
3
effect of temperature on the expression of the gene for color
4
effect of colony size on the synthesis of color pigments