You take absorbance readings on a spectrophotometer across a lehr culture of E. coli cells growing in tryptic soy broth (TSB) Your absorbance readings clearly indicate a lag phase, a log phase, and a stationary phase. You come back and take readings at 8,10,12,14+16hrs. but the absorbance number remains the same. Shouldnt it start coming down as the closed batch culture enters death phase? Whats the most likely thing that is happening?
when we establish a growth curve, we should actually plot the log of the number of viable cells vs. time. However, a spectrophotometer can only measure absorbance. Absorbance is NOT the same as the number of viable cells. Many of the cells in the tube are most likely dead, but the machine cant discriminate between a live cell and dead one. This keeps the absorbance high even into the death phase