Psychrotolerants

Psychrotolerants are microorganisms that can grow at low temperatures, including typical refrigeration temperatures, but have their optimum growth at moderate temperatures above about 15°C. They are capable of growth across a broad temperature range, often from near 0°C to 30–35°C, though their growth rate declines at higher temperatures. They are distinguished from true psychrophiles, which are adapted to cold environments with optimum growth at or below 15°C, and from mesophiles, which require moderate temperatures for rapid growth.

Physiological adaptations support growth at low temperatures, including changes in membrane lipid composition (more unsaturated fatty acids to maintain fluidity), cold-active enzymes with activity at low temperatures, expression of cold shock proteins, and accumulation of cryoprotectants such as glycerol or trehalose. These adaptations help maintain essential cellular processes when temperatures fall.

Habitats for psychrotolerants include soil, freshwater and marine environments, plant surfaces, and refrigerated foods. They are important in food microbiology because some can grow at refrigeration temperatures and contribute to spoilage or, in some cases, pose safety risks. Notable examples include Listeria monocytogenes, which can grow at 0–4°C, and several Pseudomonas species that contribute to spoilage of dairy and meat products.

In summary, psychrotolerants are versatile microorganisms capable of surviving and growing at low temperatures while preferring moderate temperatures for rapid growth. They are relevant to food safety, food spoilage, and ecological processes in cold environments.