Membranes Avoid Freezing

Biological Strategy

Bacteria

AskNature Team

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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Membranes of some microbes continue to allow diffusion at cold temperatures by having a special fatty composition that keep them relatively fluid.

“Bacteria have two skins, an outer one which is a stiff molecular mesh, through which molecules of food and water can diffuse fairly easily, and an inner one, elastic and membranous, which has to be very selectively permeable, so that nutrients can get in but the internal substances of the cell do not leak out. (This, by the way, is the skin which ice damages lethally; the outer layer is tougher and serves to keep out big molecules and to sustain the cell’s shape). The cell membrane, as it is called, includes a lot of fat in its structure, and its permeability is very much influenced by fluidity of that fat…Psychrophiles have cell membranes of a special fatty composition, such that they are relatively fluid at temperatures near freezing point–and again they pay a price: their membranes become too fluid, and begin to melt, when the environment warms to the temperatures that most bacteria prefer.” (Postgate 1994:28)