The decrease in growth rate and the cessation of growth, due to the depletion of substrate, may be described by the relationship between µ and the residual growth- limiting substrate, represented in Eq. (2.5) and in Fig. 2.4 (Monod, 1942): µµ =+ sK s/( ) smax (2.5) Where, s is the substrate concentration in the presence of the organism, K s is the substrate utilization constant, numerically equal to substrate concentration, when µ is half µ max and is a measure of the affinity of the organism for its substrate. The zone A to B in Fig. 2.4 is equivalent to the exponential phase in batch cul- ture where substrate concentration is in excess and growth is at µ max . The zone C to A in Fig. 2.4 is equivalent to the deceleration phase of batch culture where the growth of the organism has resulted in the depletion of substrate to a growth-limiting concentration which will not support µ max . If the organism has a very high affinity for the limiting substrate (a low K s value), the growth rate will not be affected until the substrate concentration has declined to a very low level. Thus, the deceleration phase for such a culture would be short. However, if the organism has a low affin- ity for the substrate (a high K s value) the growth rate will be deleteriously affected at a relatively high substrate concentration. Thus, the deceleration phase for such a culture would be relatively long. Typical values of K s for a range of organisms and
substrates are shown in Table 2.2, from which it may be seen that such values are
usually very small and the affinity for substrate is high. It will be appreciated that
the biomass concentration at the end of the exponential phase is at its highest and,
thus, the decline in substrate concentration will be very rapid so that the time period
during which the substrate concentration is close to K
s
is very short. While the con-
cept of K
s
facilitates the quantitative description of the relationship between specific
growth rate and substrate concentration it should not be regarded as a true constant.
The decrease in growth rate and the cessation of growth, due to the depletion of substrate, may be described by the relationship between µ and the residual growth- limiting substrate, represented in Eq. (2.5) and in Fig. 2.4 (Monod, 1942): µµ =+ sK s/( ) smax (2.5) Where, s is the substrate concentration in the presence of the organism, K s is the substrate utilization constant, numerically equal to substrate concentration, when µ is half µ max and is a measure of the affinity of the organism for its substrate. The zone A to B in Fig. 2.4 is equivalent to the exponential phase in batch cul- ture where substrate concentration is in excess and growth is at µ max . The zone C to A in Fig. 2.4 is equivalent to the deceleration phase of batch culture where the growth of the organism has resulted in the depletion of substrate to a growth-limiting concentration which will not support µ max . If the organism has a very high affinity for the limiting substrate (a low K s value), the growth rate will not be affected until the substrate concentration has declined to a very low level. Thus, the deceleration phase for such a culture would be short. However, if the organism has a low affin- ity for the substrate (a high K s value) the growth rate will be deleteriously affected at a relatively high substrate concentration. Thus, the deceleration phase for such a culture would be relatively long. Typical values of K s for a range of organisms and
substrates are shown in Table 2.2, from which it may be seen that such values are
usually very small and the affinity for substrate is high. It will be appreciated that
the biomass concentration at the end of the exponential phase is at its highest and,
thus, the decline in substrate concentration will be very rapid so that the time period
during which the substrate concentration is close to K
s
is very short. While the con-
cept of K
s
facilitates the quantitative description of the relationship between specific
growth rate and substrate concentration it should not be regarded as a true constant.
| status | not learned | measured difficulty | 37% [default] | last interval [days] | |||
|---|---|---|---|---|---|---|---|
| repetition number in this series | 0 | memorised on | scheduled repetition | ||||
| scheduled repetition interval | last repetition or drill |