Bacillus subtilis

Classification

Higher order taxa

Domain: Bacteria, phylum: Firmicutes, class: Bacilli, order: Bacillales, family: Bacillaceae

Genus

Bacillus subtilis

NCBI: Taxonomy

Description and significance

Bacillus subtilis are rod-shaped, Gram-positive bacteria that are naturally found in the soil. Stress and starvation is common in this environment, therefore, Bacillus subtilis has evolved a set of strategies that allow survival under these harsh conditions. One strategy, for example, is the formation of stress-resistant spores. Another strategy is the uptake of external DNA, which allow the bacteria to adapt by recombination. However, these strategies are time-consuming. Bacillus subtilis can also gain protection more quickly against many stress situations such as acidic, alkaline, osmotic, or oxidative conditions, and heat or ethanol. The alternative sigma factor ςB is a global regulator of stress response. Heat, acid, or ethanol and glucose or phosphate starvation are all stimuli that activate ςB.

Bacillus subtilis is a model organism for study endospore formation in bacteria. Endospores in Bacillus subtilis bacteria are mostly formed in the tips of protuberances extending from liquid surface pellicles. Depletion of carbon, nitrogen, or phosphorous causes the process of sporulation to begin, however, the process needs to start before the entire exhaustion of nutrients. Otherwise, the spore formation cannot be completed due to the fact that the nutrients are too low for the energy-requiring sporulation process. This allows the cells to avoid being stuck in a vulnerable position.

The formation of the endospore occurs in several stages, denoted 0 through VI. Sporulation occurs in the following fashion. First the nucleoid lengthens, becoming an axial filament. Then, the cell forms a polar septum, one-fourth of the cell length from one end, and begins to divide. The smaller product of this division is called the forespore and the larger product is called the mother cell. The mother cell is responsible for nourishing the newly formed spore. When the septum forms, 30% of the chromosome is already on the forespore side. The remaining 70% of the chromosome enters the forespore in a fashion similar to DNA transfer during conjugation. The mother cell then engulfs the forespore by acting like a phagocyte. This causes the forespore to have two cytoplasmic membranes with a thick murein layer, namely the cortex, between them. A protein spore coat and an exosporium, a membranous layer, form outside of the forespore membranes. At this time, the forespore undergoes internal changes. Lastly, the forespore leaves the mother cell upon lysis of the mother cell. A mature endospore has no metabolic activity; it is inert. It does not have any ATP or reduced pyridine nucleotides. The interior of the endospore, the core, is very dry and resistant to moisture.

Bacillus subtilis bacteria use their flagella for a swarming motility. This motility occurs on surfaces, for example on agar plates, rather than in liquids. Cells arranged next to each other can only swarm together, not individually. These arrangements of cells are called 'rafts'. In order for Bacillus subtilis bacteria to swarm, they need to secrete a slime layer which includes surfactin, a surface tension-reducing lipopeptide, as one of its components.

Genome structure

Describe the size and content of the genome. How many chromosomes? Circular or linear? Other interesting features? What is known about its sequence? Does it have any plasmids? Are they important to the organism's lifestyle?

Cell structure and metabolism

Bacillus subtilis are rod-shaped bacteria that are Gram-positive. The cell wall is a rigid structure outside the cell. It is composed of peptidoglycan, which is a polymer of sugars and amino acids. The peptidoglycan that is found in bacteria is known as murein. Other constituents that extend from the murein are teichoic acids, lipoteichoic acids, and proteins. The cell wall forms the barrier between the environment and the bacterial cell. It is also responsible for maintaining the shape of the cell and withstanding the cell's high internal turgor pressure.

Bacillus subtilis bacteria have been considered strictly aerobic, meaning that they require oxygen to grow and they cannot undergo fermentation, however, recent studies show that they can indeed grow in anaerobic conditions. Bacillus subtilis can use nitrite or nitrate as a terminal acceptor of electrons. They can also ferment. Bacillus subtilis contains to unique nitrate reductases. one is used for nitrate nitrogen assimilation and the other is used for nitrate respiration. However, there is only one nitrite reductase that serves both purposes. Bacillus subtilis is different from other anaerobes in that it undergoes fermentation without external acceptors of electrons. The cells use pyruvate dehydrogenase for pyruvate metabolism. they do not use pyruvate formate lyase like other bacteria do.

Bacillus subtilis contain catalase, an enzyme that is responsible in the catalysis of the decomposition of hydrogen peroxide to water and oxygen, and superoxide dismutase, an enzyme that catalyzes the breakdown of superoxide into oxygen and hydrogen peroxide.

Ecology

Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.

Pathology

How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

Application to Biotechnology

Does this organism produce any useful compounds or enzymes? What are they and how are they used?

Current Research

Enter summaries of the most recent research here--at least three required

References

http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=139561 Bandow, J.E., H. Brötz, M. Hecker. "Bacillus subtilis Tolerance of Moderate Concentrations of Rifampin Involves the ςB-Dependent General and Multiple Stress Response". Journal of Bacteriology. 2002 January, 184(2): 459–467.

http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=1423&lvl=3&lin=f&keep=1&srchmode=1&unlock Entrez Genome Project

http://arjournals.annualreviews.org/doi/abs/10.1146%2Fannurev.micro.52.1.165 Nakano, M.M., P. Zuber. "Anaerobic Growth of a 'Strict Aerobe' (Bacillus subtilis)". Annual Review of Microbiology. 1998 October, Vol. 52: 165-190.

http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=94387 Perez, A.R., A. Abanes-De Mello, K. Pogliano. "SpoIIB Localizes to Active Sites of Septal Biogenesis and Spatially Regulates Septal Thinning during Engulfment in Bacillus subtilis". Journal of Bacteriology. 2000 February; 182(4): 1096–1108.

Schaechter, M., J.L. Ingraham, F.C. Neidhardt. Microbe. (ASM Press, Washington, DC, 2006).

Edited by Margo Ucar, student of Rachel Larsen and Kit Pogliano