Population Measurements Are Made Using Pure Cultures
Microorganisms rarely occur in nature as a single species. Rather, they are mixed with
other species, in a so-called mixed culture most often as a biofilm.
Therefore, to study a species, microbiologists
Hydrostatic and Osmotic Pressure
Further environmental factors can influence the growth of microbial cells. Psychrophiles
in deep ocean waters and sediments are under extremely high hydrostatic pressure.
Barophiles in fact will die quite quickly at normal
The growth of many microbes depends on a plentiful supply of oxygen, and in this
respect, such obligate aerobes must use oxygen gas as the final electron acceptor to make
Microaerophiles survive in environments where the concentrat
Optimal Microbial Growth Is Dependent on Several Physical Factors
Essential physical and chemical factors influencing cell growth:
Every microbial species has an optimal growth temperature and an approximate 30
degree Celcius operating range,
3. The stationary phase:
After some days (or hours), the vigor of the population changes and, as the reproductive
and death rates equalize, the population enters a plateau, called the stationary phase.
In the respiratory tract, antibodies from the immune
Bacterial and Archaeal Cells Reproduce Asexually
The interval of time between successive binary fissions of a cell or population of cells is
known as the generation time (or doubling time). Under optimal conditions, some species
have a very fast generatio
Population Growth Can Be Measured In Several Ways
Microbial growth in a medium, can be measured by direct and indirect methods.
Scientists may wish to perform a direct microscopic count using a known sample of the culture
on a specially de
The smaller cell, the prespore, will become the mature endospore, while the larger mother
cell will commit itself to maturation of the endospore before undergoing lysis.
The prespore cell contains cytoplasm and DNA,a nd a large amount of dipicolinic acid,
Culture Media Can Be Devised to Select for or Differentiate between Microbial
In a lab, basic ingredients of the growth media can be modified in one of three ways to
provide fast and critical information about the organism causing an infection or
Growth in the microbial world usually refers to an increase in the number of individuals;
that is, an increase in the population size with each cell carrying the identical genetic
instructions of the parent cell.