THERMOPHILIC BACTERIA: CHARACTERISTICS, HABITAT, FOOD - BIOLOGY - 2024

The thermophilic bacteria are those that have the ability to grow in environments with temperatures greater than 50 ° C. The habitats of these microorganisms are very hostile places, such as hydrothermal vents, volcanic areas, hot springs and deserts, among others. Depending on the temperature range they support, these microorganisms are classified as thermophiles, extreme thermophiles, and hyperthermophiles.

Thermophiles thrive in a temperature range between 50 and 68 ° C, with their optimum growth temperature being more than 60 ° C. Extreme thermophiles grow in a range of 35 to 70 ° C, with an optimal temperature of 65 ° C, and hyperthermophiles live in a temperature range of 60 to 115 ° C, with optimal growth at ≥80 ° C.

Image on the left: Environment where thermophilic bacteria live. Image on the right: figurative representation of thermophilic bacteria. Source: Left image pxhere, right image pixabay

As examples of thermophilic bacteria in general, the following can be mentioned: Geob acillus stearotermophilus, Deferribacter desulfuricans, Marinithermus hydrothermalis, and Thermus aquaticus, among others.

These microorganisms have special structural characteristics that give them the ability to withstand high temperatures. In fact, their morphology is so different that they cannot develop at lower temperatures.

characteristics

Thermophilic bacteria have a series of characteristics that make them adapted to environments with very high temperatures.

On the one hand, the cell membrane of these bacteria has a high amount of long-chain saturated lipids. This allows them to cope with high temperatures and maintain adequate permeability and flexibility, managing to exchange substances with the environment without destroying themselves.

On the other hand, although it is known that proteins generally denature at high temperatures, the proteins present in thermophilic bacteria possess covalent-type bonds that interact hydrophobically. This characteristic provides stability to this type of bacteria.

Similarly, the enzymes produced by thermophilic bacteria are thermostable proteins, since they can exert their functions in the hostile environments where these bacteria develop, without losing their configuration.

In relation to their growth curve, thermophilic bacteria have a high reproduction rate, but have a shorter half-life than other classes of microorganisms.

Usefulness of thermophilic bacteria in industry

Today, different types of industries use enzymes of bacterial origin to carry out different processes. Some of them come from thermophilic bacteria.

Among the enzymes most frequently isolated from thermophilic bacteria with possible industrial applications are the enzymes α-amylases, xylanases, DNA polymerase, catalases, and serine proteases, all thermostable.

These enzymes are special because they are capable of acting at high temperatures, where other similar enzymes made by mesophilic bacteria would denature.

Therefore, they are ideal for processes that require high temperatures or in processes where it is essential to minimize the proliferation of mesophilic bacteria.

Examples

As an example of the use of enzymes from thermophilic bacteria in industry, we can mention the use of DNA polymerase (taq polymerase), in the polymerase chain reaction (PCR) technique.

This technique denatures DNA at high temperatures, without the risk that the taq polymerase enzyme is damaged. The first taq polymerase used was isolated from the species Thermus aquaticus.

On the other hand, thermophilic bacteria can be used to minimize the damage caused by environmental pollution.

For example, research has revealed that some thermophilic bacteria can eliminate compounds that are toxic to the environment. Such is the case of polychlorobiphenyl (a polluting substance present in plastics and refrigerants, among other compounds).

This is possible thanks to the fact that certain thermophilic bacteria can use elements such as biphenyl, 4-chlorobiphenyl and benzoic acid as a carbon source. Therefore, they degrade polychlorinated biphenyls, eliminating them from the environment.

On the other hand, these bacteria are excellent at recycling elements such as nitrogen and sulfur in the soil. Because of this, they can be used to naturally fertilize the land without the need for artificial (chemical) fertilizers.

Likewise, some researchers propose the use of thermophilic bacteria to obtain substances that generate alternative energy such as biogas, biodiesel and bioethanol through the hydrolysis of agro-industrial waste, favoring bioremediation processes.

Habitat

The habitat of thermophilic bacteria is made up of terrestrial or marine places characterized by their high temperatures. Other factors that accompany the temperature are the pH of the medium, the concentration of salts and the chemical compounds (organic and inorganic) that may be present.

Depending on the specific characteristics of the medium, a certain type of thermophilic bacteria or another will develop in it.

Among the most common habitats for this type of bacteria the following can be mentioned: hydrothermal vents, volcanic areas, hot springs, and deserts.

Feeding

Thermophilic bacteria generally require complex culture media to grow. Among the nutrients they may require are the following: yeast extract, tryptone, casamino acids, glutamate, proline, serine, cellobiose, trehalose, sucrose, acetate, and pyruvate.

An agar used for the isolation of some thermophilic bacteria is Luria-Ber-tani agar. Contains hydrolyzed casein, yeast extract, NaCl, agar, and distilled water with a pH adjusted to 7.0 ± 0.2.

Thermophilic bacteria as contaminants of processed foods

Most thermophilic bacteria are saprophytic and do not cause disease in humans. However, in the manufacture of food there may be factors that favor the proliferation of thermophilic microorganisms, which can be harmful.

To give an example, in the manufacture of dairy products, pasteurization is used as a method of decontamination of food. This method is supposed to guarantee sanitary quality; however, it is not foolproof because sporulated thermophilic bacteria can survive this process.

This is because, although the vegetative cell of most sporulated bacteria is not heat resistant, the spores are.

There are sporulated bacteria that represent a real danger for human consumption. For example, the spores of the following species: Bacillus cereus, Clostridium botulinum, Clostridium perfringens, Thermoanaerobacterium xylanolyticum, Geobacillus stearothermophilus.

Low acid canned goods are normally attacked by spore-forming anaerobic thermophilic bacteria such as Geobacillus stearothermophilus. This bacteria ferments carbohydrates and produces an unpleasant sour taste due to the production of short-chain fatty acids.

Likewise, high acid canned food can be contaminated with Clostridium thermosaccharolyticum. This microorganism is highly saccharolytic and causes bulging of the can due to high gas production.

For its part, Desulfotomaculum nigrificans also attacks canned foods. Although the can does not show any signs of tampering, when uncapping the can you can smell a strong acidic smell and a blackened food is observed. The black color is due to the fact that the bacteria produce hydrogen sulfide, which in turn reacts with the iron in the container, forming a compound of this color.

Finally, Bacillus cereus and Clostridium perfringens cause food poisoning and Clostridium botulinum secretes a powerful neurotoxin in food that, when consumed, causes death.

Examples of thermophilic bacteria

Rhodothermus obamensis

Marine bacteria, Gram negative, heterotrophic, aerobic and hyperthermophilic bacillus.

Genus Caldicellulosiruptor

Anaerobic bacteria, Gram positive, extreme thermophilic, sporulated.

Thermomicrobium class

They are aerobic hyperthermophilic bacteria, heterotrophic, with variable Gram.

Rhodothermus marinus

Gram negative, aerobic, extreme thermophilic, and halophilic bacillus. Its production of thermostable enzymes has been studied, especially for hydrolyzing polysaccharides and for DNA synthesis, both of interest to the industry.

Deferribacter desulfuricans

Anaerobic bacteria, extreme thermophilic, heterotrophic, reducing sulfur, nitrate and arsenate.

Marinithermus

Gram negative rods or filaments, extreme thermophilic, strict aerobic heterotrophic.

Thermodesulfobacterium hydrogeniphilum

Marine species, hyperthermophilic, anaerobic, Gram negative, chemolytoautotrophic (sulfate reducing), not sporulated.

Thermus aquaticus

Gram negative, hyperthermophilic, heterotrophic and aerobic bacteria. It synthesizes a thermostable enzyme used in PCR called taq DNA polymerase.

Sulfurivirga caldicuralii

Extreme thermophilic, microaerophilic chemolytoautotrophic, thiosulfate oxidant.

Geobacillus

Gram positive, sporulated, extreme thermophilic rods. Its spores are used in microbiology laboratories as a biological control to evaluate the proper functioning of the autoclave.

Gender

The species of this genus are characterized by being Gram negative, hyperthermophilic, although their growth range is wide, of marine life, they do not form spores, they are obligate anaerobes or microaerophiles.

Comparative table between the most relevant species

Source: Prepared by the author Msc. Marielsa Gil.

References

1. Gallut P. Isolation and culture of microorganisms associated with oncoids from hydrothermal springs of Santispac, Bahía Concepción, BCS, México. Thesis to obtain the degree of Master of Science. Biological Research Center. 2016. Available at: cibnor.repositorioinstitucional.
2. Bjornsdottir SH, Blondal T, Hreggvidsson GO, Eggertsson G, Petursdottir S, Hjorleifsdottir S, Thorbjarnardottir SH, Kristjansson JK. Rhodothermus marinus: physiology and molecular biology. Extremophiles. 2006; 10 (1): 1-16. Available in: cbi.nlm.nih.gov.
3. Thermus aquaticus. " Wikipedia, The Free Encyclopedia. 24 Nov 2018, 10:28 UTC. 9 May 2019, 01:55 en.wikipedia.or
4. Thwaite J, Atkins H. Sterilization test bacilli. In Medical Microbiology (Eighteenth Edition).
5. Reyes T. Marine bacterial biodiversity: new cultivable taxa. Thesis to qualify for the title of Doctor of Biotechnology. Department of Microbiology and Ecology. 2012. Available at: University of Valencia.
6. Sako Y, Takai K, Ishida Y, Uchida A, Katayama Y. Rhodothermus obamensis sp. nov., a modern lineage of extremely thermophilic marine bacteria. Int J Syst Bacteriol. nineteen ninety six; 46 (4): 1099-104.
7. Ríos M. Neida, Crespo M. Carla F., Terrazas S. Luis E., Alvarez A. María T. Isolation of thermophilic anaerobic strains that produce cellulases and hemicellulases involved in the production of Bioethanol by means of traditional culture and isolation techniques and not traditional. BIOFARBO. 2007; 15 (1): 43-50. Available at: magazinesbolivianas.org.b