What defines a halophile?

A halophile is defined as an organism that thrives in high-salt environments. These bacteria have evolved specialized mechanisms to tolerate or even require elevated concentrations of salt, which can be detrimental to most living organisms. The adaptations that enable halophiles to survive in such extreme osmotic conditions include producing compatible solutes, such as glycerol or betaine, which help to maintain cellular function despite the high external salinity.

In contrast, the other options describe different types of extremophiles or organisms with specific environmental requirements. Bacteria that thrive in acidic environments are known as acidophiles; those that survive at low temperatures are referred to as psychrophiles; and bacteria that require high oxygen levels are classified as obligate aerobes. Each of these categories emphasizes different adaptations to their respective environmental stresses, which are distinct from the adaptations seen in halophiles.