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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. Organisms that prefer extreme environments are known as extremophiles.

Habitats
The habitats of these organisms include especially cheese, yogurt, and mesophile organisms are often included in the process of beer and wine making. Since normal human body temperature is 37 °C, the majority of human pathogens are mesophiles, as are most of the organisms comprising the human microbiome.

Use of Mesophiles
Bacteria such as mesophiles and thermophiles are used in the cheesemaking due to their role in fermentation.“Traditional microbiologist use the following terms to indicate the general (slightly aribtrary optimum temperature for the growth of bacteria: psychrophiles (15-20°C), mesophiles (30-37°C), thermophiles (50-60°C) and extreme thermophiles (up to 122°C)” . Both Mesophiles and Thermophiles are used in cheese making for the same reason, however they grow, thrive and die at different temperatures. Psychrotrophic bacteria contribute to dairy products spoiling, getting mouldy or going bad due to their ability to grow at lower temperatures such as in a refrigerator. While mesophiles can survive and grow at 30°C there is a difference between the lowest temperature at which a bacteria can grow and the optimum growth temperature. Meaning that mesophiles may be able to develop and grow at a wide range of temperatures they grow much better at a smaller range of temperatures: the optimum growth temperature.

Identifying Bacteria by Temperature Range
Organisms that prefer cold environments are termed psychrophilic, those preferring warmer temperatures are termed thermophilic or thermotrophs and those thriving in extremely hot environments are hyperthermophilic. Hyperthermophiles are a type of extremophile. All bacteria have their own optimum environmental surroundings and temperatures in which they thrive the most. A genome-wide computational approach has been designed by Zheng, et al. to classify bacteria into mesophilic and thermophilic.

Many factors are responsible for a given organism's optimal temperature range, but evidence suggests that the expression of particular genetic elements (alleles) can alter the temperature-sensitive phenotype of the organism. A recently published study demonstrated that mesophilic bacteria could be genetically engineered to express certain alleles from psychrophilic bacteria, consequently shifting the restrictive temperature range of the mesophilic bacteria to closely match that of the psychrophilic bacteria. There are two explanations for thermophiles being able to survive at such high temperatures whereas mesophiles can not. The most evident explanation is that Thermophiles are believed to have cell components that are relatively more stable than the cell components of mesophiles which is why thermophiles are able to live at higher temperatures than mesophiles. “A second school of thought, as represented by the writings of Gaughran (21) and Allen (3), believes that rapid resynthesis of damaged or destroyed cell constituents is the key to the problem of biological stability to heat.

Development, Growth and Evolution of Mesophiles
Bausum proposes that mesophiles can evolve into thermophiles by growing the bacteria with specific temperature changes to trigger the conversion “The conversion from mesophilism to thermophilism by actively growing bacteria requires a brief exposure to an intermediate temperature. The nature of this adaptation was approached by examining the reverse process, namely, the change from thermophilism to mesophilism.”.

The growth of bacteria such as mesophiles and psychrophiles was also explored by Ingraham and Bailey, who quotes an experiment that found similarities between mesophiles and psychrophiles in the nature of glucose oxidation, glucose oxidation or glycolysis is the process which releases energy stored in glucose by combining it with oxygen. "[Brown] found that the temperature at which the cells of the mesophilic strain were grown affected the temperature coefficient of glucose oxidation which by resting cells. Mesophilic cells grown at a lower temperature had a lower coefficient of glucose oxidation. Since mesophilic cells grown at lower temperatures behaved more like psychrophiles, Brown doubted that the ability of psychrophiles to grow at lower temperatures was related to differences in the nature of glucose oxidation. He found, however, that cells of the psychrophilic strain grown at the same temperature as the mesophilic strain continued to exhibit a lower temperature coefficient of glucose oxidation."

An experiment conducted by Philip W. Mohrt and Steven Karawiec measured and plotted the specific growth rates of 12 bacterial species, they used the curves they plotted to esitmate maximum specific growth rates. "The forms of Arrhenius curves for the psychrophiles, psychrotrophs, some mesophiles and some thermophiles are similar. Thus, categorizing these organisms into distinct classes by their positions in a temperature spectrum is arbitrary. Furthermore, the forms of the Arrhenius curves for some mesophiles and some thermophiles are more complex than those for the psychrophiles and other mesophiles and thermophiles. The two recurrent forms of the Arrhenius curve establish uncontrived categories which can be used to classify the temperature-dependent rates of replication of bacteria." This experiment analyses the difference between the 12 different types of bacteria and pinpoints their growth rates, optimal temperature for growth. The quote provided compares and contrasts mesophiles with thermophiles and other types of bacteria.