Page 255 - Algae Anatomy, Biochemistry, and Biotechnology

238 Algae: Anatomy, Biochemistry, and Biotechnology

FIGURE 6.1 Growth curve of an algal population under batch culture conditions (a) and corresponding
variations of the growth rate (b).

The exponential growth phase normally lasts for a very short period, because cells start to shade
each other as their concentration increases. Hence, the culture enters the phase of retardation, and
cell growth rate decreases because mainly light, but also nutrients, pH, carbon dioxide, and other
physical and chemical factors begin to limit growth. Following this phase, the cell population con-
tinues to increase, but the growth rate decreases until it reaches zero, at which point the culture
enters the stationary phase, during which the cell concentration remains constant at its maximum
value. The final stage of the culture is the death or “crash” phase, characterized by a negative
growth rate; during this phase water quality deteriorates, mainly due to catabolite accumulation,
and nutrients are depleted to a level incapable to sustain growth. Cell density decreases rapidly
and the culture eventually collapses.

TABLE 6.19
Description of the Six Successive Phases of Growth for an Algal Population under Batch
Culture Conditions

Growth Rate
Phase Growth Interpretation Description
1 Lag Zero Physiological adaptation of the inoculum to changing conditions
2 Acceleration Increasing Trivial
3 Exponential Constant Population growth changes the environment of the cells
4 Retardation Decreasing Effects of changing conditions appear
5 Stationary Zero One or more nutrients (or light) are exhausted down to the
threshold level of the cells
6 Decline Negative The duration of stationary phase and the rate of decline are
strongly dependent on the kind of organisms