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 is a rod-shaped, gram-positive bacteria that is 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

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Ecology

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Pathology

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Application to Biotechnology

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Current Research

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References

[1]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.

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