Generation time

In microbiology, generation time is the period in which the number of microbes in a population doubles.

Outside of microbiology, the term refers to the average time span between two successive generations. In epidemiology , generation time is the time between an infection of a person and secondary infections that originate from them. It is usually estimated over the serial interval .

Determination of generation time

The increase in the number of individuals is given in the exponential phase by the equation

${\displaystyle \ln N=\ln N_{0}+k\cdot t\qquad \Leftrightarrow \qquad N=N_{0}\cdot \mathrm {e} ^{k\cdot t}}$

described. Here is the number of individuals at the time , the original number of individuals and the growth rate (growth constant). The equation thus results for a doubling of the number of individuals ${\displaystyle N}$ ${\displaystyle t}$ ${\displaystyle N_{0}}$ ${\displaystyle k}$

${\displaystyle \ln(2\cdot N_{0})=\ln N_{0}+k\cdot t\quad \Rightarrow \quad t={\frac {\ln 2}{k}}\approx {\frac {0{,}69}{k}}}$

To determine the growth constant, the logarithm of the number of individuals is plotted against time. For the exponential growth phase, a straight line results , the slope of which represents the growth constant.

microbiology

bacterium	Generation time
Geobacillus stearothermophilus	11 minutes
Escherichia coli	20 minutes
Treponema pallidum	4-18 hours
Mycobacterium tuberculosis	18 hours

In the case of bacteria , the generation time can be very different depending on the growth conditions and the bacterial strain. The generation time is shortest during the exponential phase of bacterial growth. The adjacent table shows examples of generation times for bacteria under optimal conditions.

The generation time of the respective bacterial culture is essentially influenced by external factors such as temperature , localization of the culture ( nutrient medium ), pH value , surface area and air composition . For industrial production, bacterial cultures are grown in a bioreactor under optimal growth conditions, thus shortening the generation time.

Invasion biology

Similar exponential growth processes can also be observed in higher organisms that live in an ecosystem without natural enemies, e.g. Example, because they by man introduced were. Examples of this are the cane toad in Australia , the water hyacinths on Lake Victoria, and various European domestic animals released by settlers in New Zealand , Tasmania , and elsewhere . The phenomenon also exists in Europe: prominent invaders are the glandular balsam , the giant hogweed known as the Hercules shrub and the Chinese woolly crab .

See also

• Rule of 72
• Half-life
• Exponential function

Individual evidence

1. ↑ Lexicon of Biology. "Generation time"
2. ↑ Steinbüchel and Opperman-Sanio (eds.): Microbiological internship: experiments and theories. Heidelberg 2003. ISBN 978-3-642-17702-6 . P. 34.