What is a key physiological trait of psychrophilic bacteria?

Psychrophilic bacteria are characterized by their ability to thrive and grow optimally at low temperatures, typically in the range of -5°C to 15°C. This adaptation allows them to inhabit cold environments, such as polar regions and deep oceans, where most other microorganisms struggle to survive.

These bacteria possess specific enzymes and cellular mechanisms that function effectively under cold conditions, which is crucial for their metabolic processes. They have adapted their membrane fluidity to maintain function at lower temperatures and often produce antifreeze proteins to prevent ice crystal formation in their cells.

The other options are based on traits not associated with psychrophilic bacteria. For example, optimal growth at high temperatures is typical of thermophilic or hyperthermophilic bacteria, while growth in the presence of light pertains to phototrophic organisms, and unusual cell structures can refer to diverse bacterial groups that don't necessarily share the cold-loving characteristics of psychrophiles.