Temperature and Microbial Growth
Growth Rate and Temperature
Bacteria may grow across a wide range of temperatures, from very cold to very hot.Learning Objectives
Describe how the growth of bacteria is affected by temperature and how bacterial growth can be measuredKey Takeaways
Key Points
- The basic means of measuring growth requires bacterial enumeration (cell counting).
- Methods for bacterial cell counting include: 1. direct and individual (microscopic, flow cytometry), 2. direct and bulk (biomass), 3. indirect and individual (colony counting), or 4. indirect and bulk (most probable number, turbidity, nutrient uptake).
- A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold. All human pathogens are mesophiles.
- Cold shock proteins help the cell to survive in temperatures lower than optimum growth temperature.
- Heat shock proteins help the cell to survive in temperatures greater than the optimum, possibly by condensation of the chromosome and organization of the prokaryotic nucleoid.
Key Terms
- mesophile: An organism, especially a microorganism, that lives and thrives at moderate temperatures.
- psychrophile: An organism that can live and thrive at temperatures much lower than normal; a form of extremophile.
- thermophile: An organism that lives and thrives at relatively high temperatures; a form of extremophile; many are members of the Archaea.
Growth Rate and Temperature

Bacterial growth curve: Bacterial growth in batch culture can be modeled with four different phases: (A) the lag phase, when the population stays roughly the same; (B) the exponential, or log, phase, when the population grows at an increasing rate; (C) the stationary phase, when population growth stagnates; and (D) the death phase, when bacteria begin to die off and the population decreases in size.

Grand Prismatic Spring, Midway & Lower Geyser Basin, Yellowstone National Park: This photo shows steam rising from hot and sterile deep azure blue water in the center, surrounded by huge mats of brilliant orange algae, bacteria and archaea. These colorful microorganisms are called extremophiles—these in particular are thermophiles.
For example, in molecular biology, the cold-shock domain (CSD) is a protein domain of about 70 amino acids which has been found in prokaryotic and eukaryotic DNA-binding proteins. Part of this domain is highly similar to the RNP-1 RNA-binding motif. When Escherichia coli is exposed to a temperature drop from 37 to 10 degrees Celsius, a four to five hour lag phase occurs and then growth is resumed at a reduced rate. During the lag phase, the expression of around 13 proteins, which contain cold shock domains is increased two- to ten-fold. These so-called cold shock proteins are thought to help the cell survive in temperatures lower than optimum growth temperature, by contrast with heat shock proteins, which help the cell survive in temperatures greater than the optimum, possibly by condensation of the chromosome and organization of the prokaryotic nucleoid.
Classification of Microorganisms by Growth Temperature
Bacteria can be classified on the basis of cell structure, metabolism or on differences in cell components.Learning Objectives
Describe how bacteria can be classified on the basis of cell structure, cellular metabolism or differences in cell components such as DNAKey Takeaways
Key Points
- A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, typically between 20 and 45 °C (68 and 113 °F).The term is mainly applied to microorganisms.
- All bacteria have their own optimum environmental surroundings and temperatures in which they thrive the most.
- Thermophiles contain enzymes that can function at high temperatures. Some of these enzymes are used in molecular biology (for example, heat-stable DNA polymerases for PCR), and in washing agents.
Key Terms
- mesophile: An organism, especially a microorganism, that lives and thrives at moderate temperatures.
- thermophile: An organism that lives and thrives at relatively high temperatures; a form of extremophile; many are members of the Archaea.
Bacteria can be classified by their optimal growth temperature. The following are the five classifications:
- Hyperthermophile (60 degrees C and upwards)
- Thermophile (optimal growth between 45 and 122 degrees)
- Mesophile (20 and 45 degrees C)
- Psychrotrophs (will survive at 0 degrees C, but prefer mesophilic temperature
- Psychrophiles (-15 and 10 degrees C or lower)

Methanopyrus kandleri
Methanopyrus kandleri can survive and reproduce at 122 °C.The Heat-Shock Response
Heat shock response is a cell's response to intense heat, including up-regulation of heat shock proteins.Learning Objectives
Describe how the bacterial stress response enables bacteria to survive adverse and fluctuating conditions in their immediate surroundings such as increases in temperatureKey Takeaways
Key Points
- The bacterial stress response enables bacteria to survive adverse and fluctuating conditions in their immediate surroundings.
- A bacterial cell can react simultaneously to a wide variety of stresses and the various stress response systems interact with each other by a complex of global regulatory networks.
- The up-regulation of HSPs during heat shock is generally controlled by a single transcription factor; in eukaryotes this regulation is performed by heat shock factor (HSF), while σ32 is the heat shock sigma factor in Escherichia coli.
Key Terms
- heat shock response: The cellular response to heat shock.
In biochemistry, heat shock is the "effect of subjecting a cell to a higher temperature than that of the ideal body temperature of the organism from which the cell line was derived. "
Heat shock response is the cellular response to heat shock includes the transcriptional up-regulation of genes encoding heat shock proteins (HSPs) as part of the cell's internal repair mechanism. HSPs are also called 'stress-proteins' and respond to heat, cold and oxygen deprivation by activating several cascade pathways. HSPs are also present in cells under perfectly normal conditions. Some HSPs, called 'chaperones', ensure that the cell's proteins are in the right shape and in the right place at the right time. For example, HSPs help new or misfolded proteins to fold into their correct three-dimensional conformations, which is essential for their function. They also shuttle proteins from one compartment to another inside the cell and target old or terminally misfolded proteins to proteases for degradation. Additionally, heat shock proteins are believed to play a role in the presentation of pieces of proteins (or peptides) on the cell surface to help the immune system recognize diseased cells. The up-regulation of HSPs during heat shock is generally controlled by a single transcription factor; in eukaryotes this regulation is performed by heat shock factor (HSF), while σ32 is the heat shock sigma factor in Escherichia coli.

Heat shock proteins: Heat shock protein come in many sizes. This is an example of small heat shock proteins produced by Pseudomonas aeruginosa Clonal Variants Isolated from Diverse Niches.