Bacterial growth is process in which two clone daughter cells are produced by the cell division of one bacterium. Hence, local doubling of the bacterial population occurs. Both daughter cells from the division do not necessarily survive. However, if the number surviving exceeds unity on average, the bacterial population undergoes exponential growth. The measurement of an exponential bacterial growth curve was traditionally a part of the training of all microbiologists.
In autecological studies, bacterial growth can be modeled with four different phases: lag phase (A), exponential or log phase (B), stationary phase (C), and death phase (D).
- During lag phase, bacteria adapt themselves to growth conditions. It is the period where the individual bacteria are maturing and not yet able to divide.
- During the exponential phase, the number of new bacteria appearing per unit time is proportional to the present population. This gives rise to the classic exponential growth curve, in which the logarithm of the population density rises linearly with time (see figure). The actual rate of this growth (i.e. the slope of the line in the figure) depends upon the growth conditions, which affect the frequency of cell division events and the probability of both daughter cells surviving. Exponential growth cannot continue indefinitely, however, because the medium is soon depleted of nutrients.
- During stationary phase, the growth rate slows as a result of nutrient depletion and accumulation of toxic products. This phase is reached as the bacteria begin to exhaust the resources that are available to them.
- At death phase bacteria run out of nutrients and die.
In reality, these phases are not so well defined, and the curve is much more continuous. Bacterial growth can be suppressed with bacteriostats, without necessarily killing the bacteria. In a synecological, a true-to-nature situation, where more than one bacterial species is present, the growth of microbes is more dynamic and continual.
==This article includes material from an article posted on 26 April 2003 on Nupedia; written by Nagina Parmar; reviewed and approved by the Biology group; editor, Gaytha Langlois; lead reviewer, Gaytha Langlois ; lead copyeditors, Ruth Ifcher. and Jan Hogle.