Geobacillus stearothermophilus

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A Microbial Biorealm page on the genus Geobacillus stearothermophilus


Higher order taxa

Bacteria (Domain); Firmicutes (Phylum); Bacilli (Class); Bacillales (Order); Bacillaceae (Family); Geobacillus (Genus) (1)


Geobacillus stearothermophilus

Description and significance

Geobacillus stearothermophilus is a gram positive thermophilic (heat loving) bacteria characterized by a inner cell membrane and a thick cell wall. G. stearothermophilus is a rod shaped anaerob found in thermophilic habitats like thermal vents. Many heat stable enzymes like xylanase for pulp treatment and thermolysin-like protease for production of artificial aspartame have been isolated from this thermophilic bacteria. (2) Geobacillus stearothermophilus strain 10, is an isolated strain that was found in a hot spring in Yellowstone National Park and has been used in comparative analysis of thermophiles and mesophiles. Geobacillus stearothermophilus is constantly used in the biotech industry to test the success of sterilization cycles of equipment. Due to the bacteria’s high resistance to heat, it is a suitable Biological Indicator of microbe life after a sterilization cycle (read more below).

Strain Geobacillus stearothermophilus JT2 when grown on blood agar plates are observed to have an ellipsoidal shape and adhere to each other to form longitudinal chains containing two or more cells. (6) This strain is observed to be highly motile and produces a highly temperature stable enzyme α-amylase (read more below). (6)

Genome structure

Genome structure for this bacteria is still being determined. This is being pursued at Tarbiat Maderes University in Tehran, Iran. (7)

Recent research conducted at Germany’s Humbolt University, has identified an ATP-binding cassette transporter in the genome of G. stearothermphilus srain DSMZ 13240. (10) Researchers isolated a gene cluster of the Gram-positive bacteria that encoded for a “high-affinity” arginine ABC-transporter complex. The ABC-transporter complex seems to be more reliable for predicting substrate specificity due to the use of a highly cognate binding protein rather than the hydrophobic subunits of the ABC-transporter. (10).

A plasmid has been isolated in Geobacillus stearothermophilus (strain TK05), named Plasmid pSTK1. The plasmid is 1,883 nucleotides in lenth and contains 44% guanine cytosine content and 56% adenosine thymine content. The plasmid carries three genes of which code for three different proteins. (3) In conjunction to this plasmid the European Food and Safty Authority assessed Bacillus bacteria with respect to saftey in the food industry and identified an antibiotic resistance gene in G. stearothermophilus on the extra chromasomal plasmid as being a moblilisable plasmid-encoded tetracyclan resistance gene. It is thought that there is a high probability that such plasmids have potent mechanisms of conjugative plasmid transfer in the genus Bacillus. Certain strains have a broad host range and harbor conjugative transposons which encode for tetracycline resistance.(11)

Cell structure and metabolism

G. stearothermophilus contain endospores which are a highly resistant dormant form of the bacteria. The bacteria produce spores under harsh conditions when nutrient levels are low. The spore core is dehydrated (10-25% water content) making it very resistant to heat and chemicals. (9) To protect the DNA Ca2+ dipcolinic acid complex and small acid-soluble proteins (SASP) bind to the spore DNA and increase the spores’ resistance to desiccation. The outside of the spore is comprised of loosely cross linked peptidoglycan which prevents hydration and acts as a permeability barrier to chemicals such as lysozyme. (9)


No pathogenic strains of Geobacillus stearothermophilus have been found so far. The bacteria is used in the production of enzymes in the commercial food industry where no foodborne cases or food saftey problems have been identified thus far. (11)

Application to Biotechnology

A strain of Geobacillus stearothermophilus isolated from Mae’en hot springs in Jordan was characterized as being one of the first α-amylase producing thermophilic bacteria. α-Amylase, an enzyme used in the production process of sweeteners from starch, is of major industrial interest. Some industrial requirements of the enzyme are that it must withstand high processing temperatures during the conversion from starch to sweetener. This necessitates the use of thermo-stable α-amylase. Strain Geobacillus stearothermophilus JT2 was isolated and grown at high temperatures (55°C) with starch as a carbon source. The bacteria grew up to high densities supporting that the thermophilic bacteria contains resident enzymes more resistant to degradation at high temperatures. (6) This is an area of ongoing research as more studies are conducted on the industrial applications of thermophilic bacteria.

The Biotechnologies industry depends greatly upon its ability to create sterile environments in which to conduct aseptic processes. Specialized equipment has been developed to sterilize equipment and areas of interest with the use of high temperatures and steam. The sterilization processes for the biotech industry is highly tested to ensure the absolute of “sterility”. Geobacillus stearothermophilis spores are widely used to test the lethality of an autoclave or other equipment performing a sterilization process. (8) The thermophilic bacteria Geobacillus stearothermophilis are highly resistant to heat and are therefore used in equipment validation studies to prove that sterilization took place. The spores used in these studies are called Biological Indicators (BI’s) and offer biological evidence for a sterilization process.

Current Research

A recent study conducted at the University of Waikato evaluated surface complexation models (SCM’s) in quantifying metal ion adsorption by thermphilic Gram-positive bacteria. Of the microorganisms studied Geobacillus stearothermophilus was observed for its heat tolerance and anaerobic metabolism. Different functional; groups within and on the bacterial cell wall may be involved in the absorption of Cadmium ions Cd+ and other toxic heavy metals. In contrast to mesophilic bacteria, a different type of functional group may be involved in the bio-absorption of cadmium. (5) By further investigating these specialized bio-absorption schemes researchers hope to develop insight for using these thermophiles to improve waste treatment of metal-polluted water and soil.

The department of Bioscience and Technology at the University of Strathclyde is evaluating the use of thermostable bacteria for the aerobic digestion of agricultural wastes to be used for animal feed supplantation. High biomass yields from G. stearothermophilus through the digestion of waste has been observed and bacteria thus enriches the end product intended for use in animal feeding.(13) Ongoing research is striving to optimize this process and evaluate in more depth the growth behavior of mixed populations in real waste siuations.(13)






5. Hetzer, A.” Cadmium Ion Biosorption by the Thermophilic Bacteria Geobacillus stearothermophilus and G. thermocatenulatus.”Applied and environmental Microbiology, June 2006, p. 4020-4027.

6. Al-Qodah, Z.”Production and characterization of thermostable α-amylase by thermphilic Geobacillus stearothermphilus” Biotechnology Journal, May 2006, p. 850-857.


8. Lemieux, P. ”Destruction of Spores on Building Decontamination Residue in a Commercial Autoclave” Appl Environ Microbial, Dec. 2006, 72(12), p. 7687-7693.

9. Zhang, J. “Sterilization using High Pressure carbon Dioxide” The Journal of supercritical Fluids, Volume 38, Issue 3, October 2006, p. 354-372.

10. Fleischer, R. “Identification of a gene cluster encoding anarginine ATP-binding-cassette transporter in the genome of the thermophilic Gram-positive bacterium Geobacillus stearothermophilus strain DSMZ 13240.” Microbiology (2005), 151, p. 835–840.

11. Hoshino, T. “Nucleotide sequence of the tetracycline resistence gene of pTHT15, a thermophilic Bacillus plasmid: comparison with stahphylocoocal TcR controls.” Gene 37, p. 131-138


13. Ugwuanyi, J. "Yield and protein Quality of thermophilic Bacillus spp. biomass related to thermophilic aerobic digestion of aggricultural wastes for animal feed supplantation" March 2007.

Edited by: Sam Timko