6.3—Bacterial growth curves and growth rate constants

A microbial culture typically passes through lag, exponential, stationary and death phases. The rate changes as cells adapt, divide rapidly, exhaust nutrients, alter pH or accumulate toxic waste.

Growth rate is a change over time, not simply the final number of cells. A constant-rate assumption is only sensible over the relevant part of the exponential phase.

A culture may show a steep increase after adaptation, then level off when oxygen or nutrients become limiting. Changing the aeration or substrate can shift the phase boundaries.

A stationary phase does not mean cells are all dead, and an optical reading is not automatically a viable-cell count. State the measured proxy and time interval.