where xn is the original biomass concentration, x, is the biomass concentration after the time interval, t hours, e is the base of the natural logarithm.

Fig. 2.1. Growth of a typical microbial culture in batch conditions.

On taking natural logarithms, equation (2.2) becomes:

Thus, a plot of the natural logarithm of biomass concentration against time should yield a straight line, the slope of which would equal fx,. During the exponential phase nutrients are in excess and the organism is growing at its maximum specific growth rate, /xm.:x, for the prevailing conditions. Typical values of fimm for a range of micro-organisms are given in Table 2.1.

It is easy to visualize the exponential growth of single celled organisms which replicate by binary fission. Indeed, animal and plant cells in suspension culture will behave very similarly to unicellular microorganisms (Griffiths, 1986; Petersen and Alfermann, 1993). However, it is more difficult to appreciate that

Table 2.1. Some representative values of nmax (obtained under the conditions specified in the original reference) for a range of organisms





Vibrio natriegens

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