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  • With a doubling time of 30 minutes and a starting population size of 1 × 10 5 cells, how many cells will be present after 2 hours, assuming no cell death?

The growth curve

Microorganisms grown in closed culture (also known as a batch culture ), in which no nutrients are added and most waste is not removed, follow a reproducible growth pattern referred to as the growth curve . An example of a batch culture in nature is a pond in which a small number of cells grow in a closed environment. The culture density is defined as the number of cells per unit volume. In a closed environment, the culture density is also a measure of the number of cells in the population. Infections of the body do not always follow the growth curve, but correlations can exist depending upon the site and type of infection. When the number of live cells is plotted against time, distinct phases can be observed in the curve ( [link] ).

A graph with time on the X axis and logarithm of living bacterial cells on the Y axis. The line of the graph begins towards the bottom of the Y axis and is flat for a short time. This is labeled 1) lag phase: no increase in number of living bacterial cells. Next the line slopes upwards. This is labeled Log phase: exponential increase in number of living bacterial cells. Next the line flattens again. This is labeled 3) Stationary phase: plateau in number of living bacterial cells; rate of cell division and death roughly equal. Final the line slopes downwards. This is labeled 4) Death or decline phase: exponential decrease in number of living bacterial cells.
The growth curve of a bacterial culture is represented by the logarithm of the number of live cells plotted as a function of time. The graph can be divided into four phases according to the slope, each of which matches events in the cell. The four phases are lag, log, stationary, and death.

The lag phase

The beginning of the growth curve represents a small number of cells, referred to as an inoculum , that are added to a fresh culture medium , a nutritional broth that supports growth. The initial phase of the growth curve is called the lag phase , during which cells are gearing up for the next phase of growth. The number of cells does not change during the lag phase; however, cells grow larger and are metabolically active, synthesizing proteins needed to grow within the medium. If any cells were damaged or shocked during the transfer to the new medium, repair takes place during the lag phase. The duration of the lag phase is determined by many factors, including the species and genetic make-up of the cells, the composition of the medium, and the size of the original inoculum.

The log phase

In the logarithmic (log) growth phase , sometimes called exponential growth phase , the cells are actively dividing by binary fission and their number increases exponentially. For any given bacterial species, the generation time under specific growth conditions (nutrients, temperature, pH, and so forth) is genetically determined, and this generation time is called the intrinsic growth rate . During the log phase, the relationship between time and number of cells is not linear but exponential; however, the growth curve is often plotted on a semilogarithmic graph, as shown in [link] , which gives the appearance of a linear relationship.

a) An arithmetic scale graph showing log phase growth. The X axis is time (hours) and the Y ais is cells per ml. The line on this graph starts fairly flat with readings of (1,2) and (5,32) but quickly slopes up steeply with a final reading of (10, 1024). B) is a semilog scale graph of log phase growth. Again the X axis is time (hours) and the Y axis is cells per ml. But the intervals of the Y axis more clearly show the difference between 10 superscript 1 and 10 superscript 3. The line on this graph is a straight line diagonally across the graph with points of (1,2), (5,32) and (10,1024) – just like the first graph. The equation for both graphs is N=2 superscript n.
Both graphs illustrate population growth during the log phase for a bacterial sample with an initial population of one cell and a doubling time of 1 hour. (a) When plotted on an arithmetic scale, the growth rate resembles a curve. (b) When plotted on a semilogarithmic scale (meaning the values on the y -axis are logarithmic), the growth rate appears linear.

Cells in the log phase show constant growth rate and uniform metabolic activity. For this reason, cells in the log phase are preferentially used for industrial applications and research work. The log phase is also the stage where bacteria are the most susceptible to the action of disinfectants and common antibiotics that affect protein, DNA, and cell-wall synthesis.

Questions & Answers

full life cycle of plasmodium parasite
Emmah Reply
what are ways of handling sharps
namugenyi Reply
never recap or bend a sharp objects
describe the process of platelet formation
Joy Reply
what is parasitic helminths
Sadiya Reply
list three categories of symbiotic relationships.
mary Reply
what's the difference between microbial intoxication and infectious diseases
dranimva Reply
microbial intoxication results when a person ingests a toxin or a poisonous substance that has been produced by a microbe while infectious disease results when a pathogen colonize the body and subsequently cause disease.
weighing balance is needed in lab of microbiology for weighing?
amna Reply
It is mainly used for media preparation and product testing purpose.
thank you for your joining
what is microbiology
Shamsuddeen Reply
study of living organisms that are too small to be visible with naked eye
microbiology is the study of microscopic organisms, either unicellular(single cell), multicellular( cell colony), or acellular (lacking cell).
is the word Atypical or a typical bacteria. .am confused pliz help
typical bacteria
okay thank you what does that mean
atypical means that it has some characters from bacteria not all characters ...but tybical means that it has all the characters that bacteria have
thank you Zulpha
some examples please
thank you Reham
1) typical bacteria contain a cell wall whereas atypical bacteria usually do not contain a cell . 2) typical bacteria can be either Gram-positive or Gram-negative while atypical bacteria remain colorless with Gram staining. 3) cells of typical bacteria are large ,while cells of the atypical small
Example of atypical : Mycoplasma pneumoniae , chlamydophila pneumoniae , legionella
what is micro biology
Jauharah Reply
is the study of organisms which can't be viewed by our necked eyes
Because it preexisting causing secondary infection after collateral damage of normal microbota
Rafaa Reply
combinations of drugs that can't be taken together and why
Grace Reply
Antagonism: the combined action is less than that of the more effective agent when used alone). All these effects may be observed in vitro (particularly in terms of bactericidal rate) and in vivo والله اعلم
....fermentros have 1-15litre capacity
AMAR Reply
which of the following microorganisms are classified as eukaryotic?
Semugab Reply
how do I see the list?
what are the choices?
dear tell us the choices
mr semugab give us the list please
what are the new discoveries of microorganisms
Ezibon Reply

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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