Bacillus stratosphericus

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A Microbial Biorealm page on the genus Bacillus stratosphericus

Classification

Figure 1: The stratified layers of the Earth’s atmosphere: troposphere, stratosphere, and upper atmosphere. The stratosphere is located approximately 30-50km above the Earth’s surface. This region is where B. stratosphericus can be found (1,5).

Higher order taxa

Bacteria; Firmicutes; Bacilli; Bacillales; Bacillaceae;

Bacillus; Bacillus stratosphericus

Species

NCBI: Taxonomy

Bacillus stratosphericus

Description and significance

Microbes are pervasive on the planet Earth, occupying incredibly exterme environments and, thus, their presence in Earth's upper atmosphere continues to demonstrate the hardiness of single-celled life. The novel species Bacillus stratosphericus can be detected in the stratosphere orbiting the Earth among satellites (1). However, B. stratosphericus is not limited to the atmosphere and can be found in an array of environments such as desert soils (2), deep seas and estuaries (1). It is endospore-forming, as many Bacillus are, and is able to withstand unfavourable conditions, permitting it to colonize and adapt to variable environments. B. stratosphericus has since become of interest for potential biotechnology applications (2) and in understanding anti-microbial sterilization via DBD plasma treatment (3). It has also been utilized in microbial fuel cells to efficiently generate electricity (4).

Cell Structure, Metabolism and Life Cycle

B. stratosphericus is a motile rod-shaped, gram positive bacterium (5). It is a facultative anaerobe capable of multiple modes of cellular respiration (5). In the absence of oxygen, energy necessary for growth can be acquired through nitrate respiration or from the fermentation (with acid production) of several carbohydrates (5). As mentioned previously, B. stratosphericus is a spore-forming bacterium capable of assuming a dormant state for survival during sub-optimal conditions. Subsequently, suitable environmental conditions allow the spore to undergo germination to acquire a metabolically active vegetative cell. B. stratosphericus’ persistence in adverse circumstances include resistance to UV radiation (3,5) and being considerably halo tolerant (2)--in which up to 17.5% NaCl is nondestructive to the cell (5). It can grow at temperatures between 8°C and 37°C, and at pH 6-10 (5). Furthermore, while certain heavy metals at high concentrations are generally toxic to most organisms, B. stratosphericus is highly tolerant to Fe, Co, Ni, and Cu ions, and moderately tolerant to Cd and Zn ions (2). Furthermore, antibiotic resistance is also characteristic of B. stratosphericus (5). A few of the common antibiotics ineffective against B. stratosphericus include penicillin, kanamycin, vancomycin, and erythromycin (5).

Phylogeny

Figure 2: A phylogenetic tree showing relationships between a few closely related Bacillus species, including B. stratosphericus. Micrococcus luteus used as the outlier. The image is a modified version from Shivaji et al., 2012 (5).

The complete genome sequence of B. stratosphericus has not yet been determined. Phylogenetic analysis based on the 16S rRNA gene sequence shows a common ancestry with two other novel Bacilli species, also isolated from the atmosphere, B. aerius, and B. aerophilus (5) (~ 98% similarity). B. stratosphericus has a 98-99% gene sequence similarity to B. licheniformis, a soil-dwelling bacterium (10), and B. sonorensis, another novel Bacillus species (5).

Applications to Biotechnology

Microbial fuel cells (MFCs) provide the means for microbes to oxidize organic materials from biomass to generate carbon dioxide and electricity (4,6). Bacteria can alternatively transfer electrons to MFC anodes (in an anoxic chamber) instead of its natural electron acceptor, such as oxygen or nitrogen via soluble electron shuttles or directly through membrane-associated components (6). The electrons are then passed through a resistor to a cathode, which transfers them to an electron acceptor—usually oxygen (6). Subsequently, an electrical current can be generated when this occurs (6). Recent studies at Newcastle University have identified B. stratosphericus to be highly efficient electricity producers (1). Of the 74 different bacterial strains isolated in this study, "B. stratosphericus" was found to be among 25 of the best exoelectrogens (4). Interestingly, Zhang et al. (2012) demonstrated that a MFC involving the combination of the 25 best exoelectrogenic isolates generate nearly twice as much electricity as a MFC involving the natural bacterial consortium (the community of the 74 isolates together). In a natural consortium, using acetate as the organic carbon source, they manage to harness a maximum of approximately 175 mWm^-2 power output and a stable power output of only 105 mWm^-2 (4). Similarly, when the 25 best exoelectrogenic bacterial strains, including B. stratosphericus, are selected to grow under the same conditions, they are able to metabolize the acetate and increase the maximum power output to 200 mWm^-2(4). This confers the importance of biofilm synergy for the potential improvement of electrical output by MFCs. Moreover, the novelty of B. stratosphericus is further reflected when comparing electrogenic capabilities to a closely related relative. B. altitudinis when grown on a MFC anode achieves a power output of approximately 6 mW·m^-2, while "B. stratosphericus" is able to propagate a much higher power production of 87.5 mW·m^-2 (4). Although now only producing enough power comparable to operating a small device like a calculator, MFCs may provide valuable future applications. Especially in bioremediation of contaminated environments where the metabolism of organic waste compounds or sewage can be efficiently converted to electricity without the production of harmful byproducts (6).

Figure 3:SEM image of anode surface laden with electricigens in a Microbial Fuel cell. Image credit: Newcastle Univeristy http://www.popularmechanics.co.za/sci-tech-news/bugs-from-space-offer-new-source-of-power/

Panspermia and Space

With the ability to take residence in the stratosphere and to form highly resistant spores to temperature change, desiccation, and UV radiation, Bacillus species along with Deinococci bacteria have lead to the exploration of their survival in outer space (7). Yang et al. (2009) are currently investigating the possibility of interplanetary transfers of microorganisms and the Panspermia Hypothesis. The Panspermia Hypothesis proposes the idea that life on earth originated from deposits of bioorganic molecules or microorganisms in space (8). This concept generally involves two theories for the mechanistic transport of these entities: lithopanspermia, which is the transport of these bioorganic molecules and microorganisms within meteorites, and radiopanspermia, which is the dispersal of spores by starlight (8,9). Although Panspermia has not yet been proven, current research persists to investigate the limitations of these impervious spores to determine the likelihood of their survival in hostile interstellar space conditions.

References

1 Fuel cells from stratospheric bacteria." Industrial Bioprocessing 6 Apr. 2012. Business Insight: Essentials. October 26, 2012 http://bi.galegroup.com.ezproxy.library.ubc.ca/essentials/article/GALE%7CA286720036/4081782c52161ed11a24196958c0925d?u=ubcolumbia

2 Moreno, M., Piubeli, F., Bonfa, M., Garcia, M., Durrant, L., and Mellado, E. “Analysis and characterization of cultivable extremophilic hydrolytic bacterial community in heavy-metal contaminated soils from the Atacama Desert and their biotechnological potentials” Journal of Applied Microbiology, 2012, doi:10.1111/j.1365-2672.2012.05366.x

3 Zhang, J., Zhang, E., Scott, K., and Burgess, J. “Enhanced Electricity Production by Use of Reconstituted Artificial Consortia of Estuarine Bacteria Grown as Biofilms.” Environmental Science & Technology, 2012, DOI:10.1021/es2020007

4 Cooper, M., Fridman, G., Fridman, A., and Joshi, S.G. “Biological responses of Bacillus stratosphericus to Floating Electrode-Dielectric Barrier Discharge Plasma Treatment.” Journal of Applied Microbiology, 2010, doi: 10.1111/j.1365-2672.2010.04834.x

5 Shivaji, S., Chaturvedi, P., Suresh, K., Reddy, G., Dutt, C., Wainwright, M., Narlikar, J., and Bhargava, P. “Bacillus aerius sp. nov., Bacillus aerophilus sp. nov., Bacillus stratosphericus sp. nov. and Bacillus altitudinis sp. nov., isolated from cryogenic tubes used for collecting air samples from high altitudes.” IJSEM, 2006, doi: 10.1099/ijs.0.64029-0

6 Lovley, D., “Bug Juice: Harvesting Electricity with Microorganisms.” Nature Reviews Microbiology, 2006, doi:10.1038/nrmicro1442

7 Yang, Y., Yokobori, S., and Yamagishi, A. “Assessing Panspermia Hypothesis by Mcroorganisms Collected from the High Altitude Atmosphere.” Biological Sciences in Space, 2009, DOI: http://dx.doi.org/10.2187/bss.23.151

8 Raulin-Cerceau, F., Maurel, M., and Schneider, J. “From Panspermia to Bioastronomy, the Evolution of the Hypothesis of Universal Life.” ORIGINS OF LIFE AND EVOLUTION OF BIOSPHERE, 1998, DOI: 10/10.1023/

9 Parsons, P., “Dusting off Panspermia.” Nature Journal (London), 1996, DOI: 10.1038/383221a0

10 Rey M., Ramaiya P., Nelson B., Brody-Karpin S., Zaretsky E., Tang M., Lopez de Leon A., Xiang H., Gusti V., Clausen I., Olsen P., Rasmussen M., Andersen J., Jørgensen P., Larsen T., Sorokin A., Bolotin A., Lapidus A., Galleron N., Ehrlich S., and Berka R. “Complete genome sequence of the industrial bacterium Bacillus licheniformis and comparisons with closely related Bacillus species.” Genome Biology, 2004, DOI: 10.1186/gb-2004-5-10-r77

Edited by Jane Nguyen, student of the University of British Columbia, Department of Microbiology and Immunology