A Microbial Biorealm page on the genus Bacillus circulans
Higher order taxa
Bacteria (Domain), Firmicutes (Phylum), Bacilli (Class), Bacillales (Order), Bacillaceae (Family), Bacillus (Genus) .
Description and significance
In 1890, Bacillus circulans was discovered and named circulans because the interior of the colonies flowed in a circular pattern. Bacillus circulans is a bacteria species in the family Bacillaceae . The bacterium is a gram-positive, rod shaped cell, and motile by peritrichous flagella  . The cells are 2.0-4.2 x 0.5-0.8 μm in size. Bacillus circulans also produces endospores . Bacillus circulans is found in soil, sewage, food, and infant bile . This bacterium is also isolated from the gut of bee larvae . Bacillus circulans is a know pathogen; causing fatal sepsis in an immunocompromised patient in 2011 .
The 16 s rRNA of Bacillus circulans strain RIGLD BCI was partially sequenced when the bacteria was isolated in a patient with renal failure . There were 1397 base pairs from this sequence, and the DNA was reported to be linear . From the partial sequence, it was discovered that B. circulans closest relative is Bacillus subtilis with 97% 16 s rRNA similarity . The complete genome of B. subtilis is 4,214,810 base pairs, and has 4,100 protein-coding genes . The largest gene family contains 77 putative ATP-binding transport proteins . Many of the genes code for the synthesis of secondary metabolites, which includes antibiotics, this is true from many Bacillus species .
Cell and colony structure
B. circulans is a gram-positive rod that is motile by peritrichous flagella . The cells are 2.0-4.2 x 0.5-0.8 μm in size . When grown at 30°C colonies are 1-3 mm in diameter, opaque, cream colored and also slightly convex, with irregular margins . The growth on nutrient agar is thin, and in some strains it spread actively .
Bacillus circulans is a facultative anaerobe . This means that it can make ATP (Adenosine Triphosphate) by aerobic respiration if oxygen is present, but it can switch to anaerobic respiration if oxygen is absent .
The growth temperature ranges from 5°C-20°C and 35°C-50°C with an optimum growth temperature range of 30°C -37°C . There is growth at a pH ranging from 6-9, but a pH of 7 is optimal . B. circulans grows at 7% NaCl . This bacterium produces endospores; they can be ellipsoidal, sub terminal or terminal . Spores allow bacteria to lie dormant for extended periods of time when living conditions are unfavorable, but when conditions become favorable again the endospore can reactivate itself into its vegetative stage . It is found in numerous amounts in soil, but spores can also be isolated from sewage, food and infant bile. Sometimes the spores are found in bee larvae .
Bacillus circulans is an opportunistic pathogen . Bacillus circulans caused sepsis in an immunocompromised patient in 2011, which later lead to that patients death . It also caused a wound infection in 1985 . This bacterium is also know to cause bacteremia, abscesses, and can cause meningitis in humans  
 Alebouyeh, M., Orimi, P., Azimi-rad, M., Tajbakhsh, M., Tajeddin, E., Sherafat, S., . . . Zali, M. (n.d.). Fatal sepsis by Bacillus circulans in an immunocompromised patient. Retrieved October 6, 2015.
 "Bacterial Endospores." Bacterial Endospores. Cornell University, 6 Mar. 2015. Web. 10 Dec. 2015.  [Gordon RE, Haynes WC, Pang CH-N: The genus Bacillus. U.S. Department of Agriculture Agricultural Handbook no. 427. U.S. Department of Agriculture, Washington DC, 1973]
 Vos, P. (2009). The Firmicutes. In Bergey's manual of systematic bacteriology (2nd ed., Vol. 3, pp. 21-127). NY: Springer.
Created by Jessica Prescott of Dr. Lisa R. Moore, University of Southern Maine, Department of Biological Sciences, http://www.usm.maine.edu/bio