Geobacillus stearothermophilus

Geobacillus stearothermophilus (previously Bacillus stearothermophilus)[1][2] is a rod-shaped, Gram-positive bacterium and a member of the division Firmicutes. The bacterium is a thermophile and is widely distributed in soil, hot springs, ocean sediment, and is a cause of spoilage in food products. It will grow within a temperature range of 30 to 75°C. Some strains are capable of oxidizing carbon monoxide aerobically. It is commonly used as a challenge organism for sterilization validation studies and periodic check of sterilization cycles. The biological indicator contains spores of the organism on filter paper inside a vial. After sterilizing, the cap is closed, an ampule of growth medium inside of the vial is crushed and the whole vial is incubated. A color and/or turbidity change indicates the results of the sterilization process; no change indicates that the sterilization conditions were achieved, otherwise the growth of the spores indicates that the sterilization process has not been met. Recently a fluorescent-tagged strain, Rapid Readout(tm), is being used for verifying sterilization, since the visible blue fluorescence appears in about one-tenth the time needed for pH-indicator color change, and an inexpensive light sensor can detect the growing colonies.

Geobacillus stearothermophilus
Scientific classification
G. stearothermophilus
Binomial name
Geobacillus stearothermophilus

Biological indicators are used in conjunction with chemical indicators and process indicators to validate sterilization processes.

It was first described in 1920 as Bacillus stearothermophilus,[3] but, together with Bacillus thermoglucosidasius, it was reclassified as a member of the genus Geobacillus in 2001.[4]

Applications in molecular biology

DNA Polymerase

DNA polymerase I
OrganismGeobacillus stearothermophilus
Thermostable Group II Intron Reverse Transcriptase GsI-IIC
OrganismGeobacillus stearothermophilus

Recently, a DNA polymerase derived from these bacteria, Bst polymerase, has become important in molecular biology applications.

Bst polymerase has a helicase-like activity, making it able to unwind DNA strands. Its optimum functional temperature is between 60 and 65°C and it is denatured at temperatures above 70°C. These features make it useful in loop-mediated isothermal amplification (LAMP).[5] LAMP is similar to the polymerase chain reaction (PCR) but does not require the high temperature (96°C) step required to denature DNA.

Reverse transcriptase

In 2013, a thermostable group II intron reverse transcriptase (TGIRT), GsI-IIC-MRF, from G. stearothermophilus was found to retain activity up to 70°C and to exhibit high processivity and a low error rate.[6] These properties make this enzyme useful for reverse transcribing long and/or highly structured RNA molecules. A method for determining RNA secondary structure, DMS-MaPseq, uses this enzyme because it converts normal RNA to DNA accurately but introduces mutations at unpaired bases that have been methylated by dimethyl sulfate, and the mutations can be identified via sequencing.[7]


  1. Coorevits, A; Dinsdale, AE; Halket, G; Lebbe, L; De Vos, P; Van Landschoot, A; Logan, NA (July 2012). "Taxonomic revision of the genus Geobacillus: emendation of Geobacillus, G. stearothermophilus, G. jurassicus, G. toebii, G. thermodenitrificans and G. thermoglucosidans (nom. corrig., formerly 'thermoglucosidasius'); transfer of Bacillus thermantarcticus to the genus as G. thermantarcticus comb. nov.; proposal of Caldibacillus debilis gen. nov., comb. nov.; transfer of G. tepidamans to Anoxybacillus as A. tepidamans comb. nov.; and proposal of Anoxybacillus caldiproteolyticus sp. nov". International Journal of Systematic and Evolutionary Microbiology. 62 (Pt 7): 1470–85. doi:10.1099/ijs.0.030346-0. PMID 21856988.
  2. "Notification that new names and new combinations have appeared in volume 50, part 2, of the IJSEM" (PDF). International Journal of Systematic and Evolutionary Microbiology. 51 (3): 795–6. 2001. doi:10.1099/00207713-51-3-795. PMID 11411700.
  3. DONK P.J.: A highly resistant thermophilic organism" Journal of Bacteriology 1920; 5, 373-374.
  4. T. N. Nazina; T. P. Tourova; A. B. Poltaraus; E. V. Novikova; A. A. Grigoryan; A. E. Ivanova; A. M. Lysenko; V. V. Petrunyaka; G. A. Osipov; S. S. Belyaev & M. V. Ivanov (2001). "Taxonomic study of aerobic thermophilic bacilli: descriptions of Geobacillus subterraneus gen. nov., sp. nov. and Geobacillus uzenensis sp. nov. from petroleum reservoirs and transfer of Bacillus stearothermophilus, Bacillus thermocatenulatus, Bacillus thermoleovorans, Bacillus kaustophilus, Bacillus thermodenitrificans to Geobacillus as the new combinations G. stearothermophilus, G. th". International Journal of Systematic and Evolutionary Microbiology. 51: 433–446. doi:10.1099/00207713-51-2-433. PMID 11321089.
  5. Mori Y, Hirano T, Notomi T (2006). "Sequence specific visual detection of LAMP reactions by addition of cationic polymers". BMC Biotechnol. 6: 3. doi:10.1186/1472-6750-6-3. PMC 1373654. PMID 16401354.
  6. Mohr, S.; Ghanem, E.; Smith, W.; Sheeter, D.; Qin, Y.; King, O.; Polioudakis, D.; Iyer, V. R.; Hunicke-Smith, S.; Swamy, S.; Kuersten, S. (2013-07-01). "Thermostable group II intron reverse transcriptase fusion proteins and their use in cDNA synthesis and next-generation RNA sequencing". RNA. 19 (7): 958–970. doi:10.1261/rna.039743.113. ISSN 1355-8382. PMC 3683930. PMID 23697550.
  7. Zubradt, Meghan; Gupta, Paromita; Persad, Sitara; Lambowitz, Alan M; Weissman, Jonathan S; Rouskin, Silvi (2016-11-07). "DMS-MaPseq for genome-wide or targeted RNA structure probing in vivo". Nature Methods. 14 (1): 75–82. doi:10.1038/nmeth.4057. ISSN 1548-7091.

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