Spores Provide Dormancy at High Temperature

Biological Strategy

Bacteria

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Regulate Cellular Processes

Cells are the basic building blocks of all living systems, so cellular processes dictate how physiological processes occur within those systems. Cells (whether entire unicellular organisms or parts of multicellular living systems) grow, metabolize nutrients (that is, chemically transform them), produce proteins and enzymes, replicate, and move. Cells as part of multicellular systems rarely act alone, instead having ways to signal to start and complete simple to quite complex interactions. How skin heals is a good example of the role of cellular processes. Blood cells called platelets release clotting factors to stop the bleeding; white blood cells rid the area of foreign materials and release molecules to coordinate healing; cells called fibroblasts start rebuilding using proteins called collagen; new blood vessels form; and skin cells called keratinocytes create the new surface.

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Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Bacteria

Domain Bacteria (“small staff”): L. acidophilus, Staphylococcus

From inside of our own bodies to the deepest parts of the ocean, bacteria have adapted to almost every possible environment. All bacteria are unicellular, microscopic, and lack a membrane-bound nucleus and organelles, and come in three basic shapes: spherical (cocci), rod (bacilli), and spiral (spirilla). Some strains can be deadly, like Staphylococcus aureus (MRSA) while others, like Lactobacillus acidophilus, found in our intestinal microbiome, keep us healthy. Cyanobacteria, also known as blue green algae, caused the Great Oxidation Event 2.4 billion years ago, producing Earth’s first oxygenated atmosphere.

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Spores that form in Bacillus type bacteria provide dormancy at high temperature because enzyme proteins change shape as the spore dehydrates.

Can relaxation make you tougher? Yes, research shows, if you are a bacterial endospore (also simply referred to as a “spore”). Endospores are tough dormant structures that form inside the cell wall of certain types of bacteria, such as Bacillus bacteria. These tough capsules form in response to adverse conditions such as drought or high temperatures. They are also resistant to ultraviolet radiation, desiccation, extreme freezing, and chemical disinfectants. Analysis of enzyme structures within endospores suggests that reversible relaxation of their three-dimensional structure is the strategy Bacillus bacteria use to survive at temperatures deadly to non-spore forming cells.

When exposed to higher temperatures, such as that of boiling water, the internal bonds of the bacteria’s folded enzyme relax to form long chains of molecules. These chains move about freely in the low water content of an endospore’s core region. Since the functional enzyme shape has relaxed, the cell machinery stops and the dormant state associated with the endospore is the result. When cell temperature becomes more hospitable, the protein chains refold back into the the normal enzyme structure. At this point, the cell returns to normal functioning.

Bertil Halle, the lead scientist for this study, sums up the connection between partial dehydration, increased temperatures, and dormancy in Bacillus bacterial endospores by stating, “‘What we have discovered is that the water in the spore is nearly as fluid as in regular bacteria, while the enzymes are largely immobile. We therefore think that spores’ heat resistance and ability to shut down their cell machinery can be ascribed to the fact that certain critical enzymes do not function in the low water content in the spore core. But much more work is needed to figure out the details of the mechanism.’” (Viegas 2009)

This summary was contributed by Sue White.

Last Updated September 28, 2016

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Reference

“The bacterial spore, the hardiest known life form, can survive in a metabolically dormant state for many years and can withstand high temperatures, radiation, and toxic chemicals. The molecular basis of spore dormancy and resistance is not understood, but the physical state of water in the different spore compartments is thought to play a key role…Spore dormancy therefore cannot be explained by glass-like quenching of molecular diffusion but may be linked to dehydration-induced conformational changes in key enzymes. The data demonstrate that most spore proteins are rotationally immobilized, which may contribute to heat resistance by preventing heat-denatured proteins from aggregating irreversibly…The quantitative results reported here on water mobility and transport provide important clues about the mechanism of spore dormancy and resistance, with relevance to food preservation, disease prevention, and astrobiology.” (Sunde et al. 2009: 19334)

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