Bacillus stearothermophilus

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*Geobacillus stearothermophilus* (or *Bacillus*
stearophilus*) is a rod-shaped, Gram-positive, spore-forming bacterium, that*
is able to grow either singly or in chains. [9] The cell wall structures of
this bacterium are consistent with features found on typical Gram-positive
bacterium. That is, they have a thick peptidoglycan layer surrounding their
cytoplasmic lipid membrane. However, the *G. stearothermophilus* Gram
stain reaction may vary between positive and negative. [9] This bacterium is
also motile, aerobic, and both catalase and oxidase positive. [9] The colonies
of *G. stearothermophilus* can grow into various shapes and
sizes, and in addition, pigments may be formed on certain media. [9]

*G. stearothermophilus* grow in temperatures
ranging from 30-75 degrees C, with an optimal growth temperature at 55°C. This
thermophile can be found in many various warm environments, including: sand,
ocean vents and hot springs, and has been observed to have to survived
temperatures as high as 130 degrees C [1]. Clinically, it is extremely
significant because it is used to used to verify that laboratory sterilization
processes are working properly. Both biological and chemical indicators are
used to determine the presence of *G. stearothermophilus'* spores
on surfaces that have undergone a sterilization process. [1]

*G. stearothermophilus* is also significant
because of its role in food spoilage, mostly milk and dairy. During the
pasturization process of these products, dairy is often heated to temperatures
that denature the molecules of pathogenic bacteria. However, *G.*
stearothermophilus'*unusually heat-tolerant enzymes and proteins allow*
it to survive this process. [5,6]

Since *Geobacillus stearothermophilus* is a
Gram-positive bacteria, its cell wall has a thick peptidoglycan layer [3]. This
peptidoglycan layer contains DAP, or meso-diaminopimelic acid, and has a
substantial amount of teichoic acids bonded to muramic acid residues, which
helps the cell wall during cell division [3]. The cell surface of this microbe
contains a capsule, a S-layer, proteins, as well as several layers of
peptidoglycan. The genus *Geobacillus* have S-layers, which are
crystalline layers of surface proteins and like the S-layers of other bacteria,
the role of these S-layers is unknown but thought to be connected to the
adherence of the bacterial cell [3]. The capsules of *Geobacillus*
stearothermophilus*are easily observed using light microscopy*
especially if this bacteria is prepared on growth media that allows for heavy
capsule production [3].

*G. stearothermophilus* is an aerobic,
spore-forming bacterium, that is a chemoautotroph. It is able to complete
respiration using simple organic compounds such as sugars, amino acids, and
organic acids, and with oxygen as the terminal electron acceptor. [3,9] *G.*
stearothermophilus*can grow over a range of pH from 2 to 11, and its*
generation time under optimal growing conditions is about 25 minutes. It is
easily grown and isolated in the typical bacteriology laboratory. [3] It is
mobile via the use of peritrichous flagella and through the process of
chemotaxis using the flagella. [3] *G. stearothermophilus* is a
spore-forming bacterium, so it is able to form an endospore during a time of
nutrient depletion. Therefore they do not form endospores normally during cell
division and active growth. [3]

*Geobacillus stearothermophilus* was originally
named *Bacillus stearothermophilus* until 2001 when a group of
scientists from Moscow began analyzing the microbial ecology of the high
temperature oil fields located in Kazakhstan. [9] These scientists were
studying these oil fields since the microbial ecology was hindering the oil
production at the fields by corroding metal equipment and reducing the quality
of local petroleum. [9] After the injection of heated water from the Caspian
Sea to replace the original water in these fields, the scientists discovered
increased and diverse microbial growth. [9] The hot, salty, and oxygenated
water favored the growth of aerobic, endospore-forming thermophiles. [9] After
genetic and physiological analysis, the scientists determined part of the
microbial growth included *Bacillus stearothermophilus*. After a
thorough examination of the microbe, they found it to be a separate taxon
as *Geobacillus* based on consistent morphology, physiology, and
phylogeny. [9] *G. stearothermophilus* had been previously
named *Bacillus stearothermophilus* in 1986, however it was
officially renamed *Geobacillus stearothermophilus* after the 2nd
edition of Bergey's Manual of Systematic Bacteriology in 2004 [3].

*G. stearothermophilus* is widely distributed
throughout nature and has been isolated from several significant locations in
the United States: rotting wood in Florida, soil using enrichment techniques,
and hot springs in Yellowstone National Park. [9] These locations demonstrate
its characteristics of being a denitrifier, having an ability to grow in
various hot environments, and having the name *Geobacillus* where *Geo* means
"earth". [9]

stearothermophilus" has been discovered to be one of the species of *Bacillus* that
is capable of mediating generalized transduction as a bacteriophage.

### Current Research:

A widely used enzyme in the dairy industry, β-Galactosidase,
which is commonly refered to as lactase, catalyzes the hydrolysis of
β-galactosides into monosaccharides [7,11]. In the case of the dairy industry,
its importance lies in the fact that it breaks down lactose, the primary sugar
in dairy, into glucose and galactose. The study found that certain metal
cations are not capable of activating this thermostable enzyme, whereas some
divalent metal ions, including: Fe(2+), Zn(2+), Cu(2+), Pb(2+), and Sn(2+) have
actually been shown to have inhibited its activity [11]. During milk
processing, this thermostable enzyme is able to assist with both the hydrolysis
of lactose, as well as the formation of galactooligosaccharides [11]. This
ongoing study in China finds that *Geobacillus stearothermophilus* IAM11001
is able to secrete cytoplasmic β-galactosidase extracellularly in certain
conditions being currently investigated [7].

### Cool factor:

*G. stearothermophilus* as a thermophilic bacillus
that holds much potential for biotechnological applications. Further research
into its biology could yield fundamental understanding about the ecology of
extreme environments and astrobiology. [9] Clinically, it is extremely
significant because it is used to verify that laboratory sterilization
processes are working properly. *G. stearothermophilus* is used
as a sterilization standard because it amazingly has been observed to have
formed endospores and survived in temperatures as high as 130 degrees C. Both
biological and chemical indicators are used to determine the presence of *G.*
stearothermophilus'*spores on surfaces that have undergone a*
sterilization process [1,9]. It also commonly serves as a biological indicator
biological indicator for the cleanliness of streams and rivers, as well as a
primary source of heat-stable enzymes that are used in industrial
applications.