This study compared the physiological characteristics of Leucothrix mucor, a marine bacterium that grows on seaweeds, measured directly in nature versus in laboratory cultures. Using tritiated thymidine autoradiography, researchers examined temperature, salinity, and pH optima in natural environments at Puget Sound, Washington and Loch Ewe, Scotland, and compared results with laboratory-cultured strains. Laboratory cultures from various global locations all showed temperature optima around 28°C regardless of their origin. However, natural populations exhibited significantly lower temperature optima ranging from 6.5°C to 25°C depending on habitat characteristics. Attempts to induce low-temperature adaptation in laboratory cultures failed, suggesting environmental factors in nature differ substantially from laboratory conditions. In contrast, salinity and pH optima measured in natural environments matched those of laboratory cultures, with optima around 31 parts per thousand salinity and pH 7-8. The findings emphasize that laboratory culture characteristics may not accurately reflect organism behavior in natural environments, particularly for temperature responses. This discrepancy may reflect selective isolation of warm-adapted strains during culturing rather than physiological adaptation in nature.

Key findings

• Laboratory cultures of L. mucor showed uniform temperature optima around 28°C regardless of source habitat, while natural populations exhibited optima ranging from 6.5°C to 25°C depending on local environmental conditions
• Laboratory cultures failed to develop low-temperature adaptation even after 15 generations of growth at low temperatures, suggesting fundamental differences between culture and natural environments
• Salinity and pH optima were consistent between laboratory cultures and natural populations, indicating these parameters are less affected by culture conditions than temperature
• The discrepancy between laboratory and natural temperature optima may result from selective isolation of warm-adapted strains rather than true physiological adaptation in natural populations