Microbes temperature tolerance

There are three environments on Earth where microbes have been identified with temperature tolerances in a range of 100°C to 121 °C, namely, submarine hydrothermal vents, the subterranean deep biosphere, and terrestrial hot springs (Table 4.1). The highest temperature tolerances (110-121 °C) are found in microbes from marine hydrothermal vents and the subterranean deep biosphere high pressures prevent these waters from boiling at 100 °C, the normal boiling point of water at 1.01 bar (1 atm) pressure. From terrestrial hot springs, microbes have been isolated that can tolerate temperatures up to 103°C (Table 4.1). 

Jahnke J, Baumann M (1987) Differentiation between Phaeocystis pouchetii (Har.) Lagerheim and Phaeocystis globosa Scherffel. Colony shapes and temperature tolerances. Hydrobiol Bull 21 141—147 Jakobsen HH, Tang KW (2002) Effects of protozoan grazing on colony formation in Phaeocystis globosa (Prymnesiophyceae) and the potential costs and benefits. Aquat Microb Ecol 27 261-273 Jones PGW, Haq SM (1963). The distribution of Phaeocystis in the eastern Irish sea. J Cons Intern Expl Mer 28 8-20... 

In designing an efficient SSF system for the conversion of cellulose to ethanol, the fermentation temperature should be compatible with the saccharification temperature that is generally between 45 and 55 °C. The optimal temperature for the most commonly available cellulase is about 50 °C. Therefore, the use of high-temperature-tolerant microbes is desirable for the application of the SSF process to ethanol production. Typical industrial ethanol-producing yeast strains are mesophiHc with an optimal fermentation temperature of 30-37°C. Only a few yeast strains that are thermotolerant, as well as good ethanol fermenters, have been described. However, some thermophilic bacterial species are known to produce ethanol from cellulosic-derived carbohydrates [68,69]. 

The phyllosphere (or aerial) parts of plants represent a challenge for the survival of microbes. The exposure to high doses of UV, fluctuations in temperature, and relative humidity all compromise viability (Heaton and Jones, 2008 Whipps et ah, 2008). Bacteria (epiphytes) that exist within the phyllosphere have evolved specialized mechanisms to improve stress tolerance and nutrient acquisition. Pseudomonas spp. form the predominant bacterial population recovered on the leaves of plants (Brandi and Amundson, 2008 Lindow and Brandi, 2003). Epiphytic pseudomonad s produce fluorescent or pigmented compounds that afford protection to UV. 

Some bacteria specifically utilize oxygen bound in the sulfate complex of a compound. As a result of this metabolic activity, sulfur is reduced to H2S. For this reason, these microbes are called sulfate-reducing bacteria (SRB). They can tolerate temperatures as high as 80°C (176°F) and environments from about pH 5 to pH 9. Species such as Desulfivibrio and Desulfomonas are examples of SRB. 

Listeria spp. is probably one of the most seriously treated food-borne pathogens due to its ability to cause listeriosis, a condition with flu-like symptoms which can compromise the human immune system especially in pregnant women, children and the elderly. Mortality rates from full listeriosis are at 20% prompting the USDA and FDA to set a "zero tolerance" against the pathogen. Detection of this microbe is therefore more important than enumeration. In food. Listeria spp. can grow even at refrigerated temperatures and have been isolated from meat and cheese products. 

The characteristics of ideal ethanol fermentation microbes include rapid fermentation, strong ethanol tolerance, few by-products, and strong tolerance of osmotic pressure and temperature. The efficient processes for converting glucose into ethanol all use yeast, such as Saccharomyces cerevisiae and Kaersibo yeast... 

Metabolic engineering and classical selection of the methylotrophic thermo-tolerant yeast Hansenula polymorpha for improvement of high-temperature xylose alcoholic fermentation. Microb. Cell Fact, 13, 122. 

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