A spore from the bacterium Bacillus subtilis shows four outer layers that protect the cell from harsh environmental conditions.
Bacillus subtilis is a ubiquitous bacterium commonly recovered from water, soil, air, and decomposing plant residue. The bacterium produces an endospore that allows it to endure extreme conditions of heat and desiccation in the environment. B. subtilis produces a variety of proteases and other enzymes that enable it to degrade a variety of natural substrates and contribute to nutrient cycling. However, under most conditions the organism is not biologically active but exists in the spore form (Alexander, 1977). B. subtilis is considered a benign organism as it does not possess traits that cause disease. It is not considered pathogenic or toxigenic to humans, animals, or plants. (epa.gov)
Photo Credit: Patrick Eichenberger, New York University (NIH/NIGMS Image Gallery)