Psychrophile

A psychrophile is a type of extremophilic organism which thrives at what is considered to be unusually cold temperatures. They can be contrasted with thermophiles, which thrive at unusually hot temperatures.

There are generally considered to be two groups of psychrophiles: "classic" psychrophiles and a second group that are sometimes referred to as psychrotrophs by food microbiologists. Classic psychrophiles are those organisms having a growth temperature optimum of 15°C or lower - and do not grow in a climate beyond a maximum temperature of 20°C. They are largely found in icy places (such as in Antarctica) or at the freezing bottom of the ocean floor.

Psychrotrophs can grow at 0°C up through approximately 40°C, and exist in much larger numbers than classic psychrophiles. They are of particular significance to food microbiologists as they can grow in refrigerated environments and cause food spoilage.