Bacterial growth rates and temperature optima in a stream with a fluctuating thermal regime1

Direct measurement of bacterial growth rates in a natural stream showed that the unicellular and filamentous populations had doubling times of 42–51 hr when the water temperature was 0–5°C, 8.4–10.8 hr when water temperature was predominantly 11–16°C, and 2.8–6.0 hr when the water temperature was 16.5–21.0°C. The populations were not optimally adapted to the prevailing stream water temperature, but rather to temperatures 5–20°C higher.