Temperature response of an associative N2-fixing Pseudomonas species in pure culture
The growth rate and nitrogenase (acetylene reduction) activity of a pseudomonad isolated from the rhizosphere of the grass species Deschampsia caespitosa were investigated in the 0–35 °C temperature range. Growth was detected from 5 to 30 °C with or without provision of fixed N and its optimum growth temperature was about 25 °C, establishing its psychrotrophic response to temperature. Maximum nitrogenase activity was also found at about 25 °C. Low but significant nitrogenase activity was detected below 15 °C. This organism was confirmed to be a microaerobic diazotroph and it was sensitive to a dissolved O2 concentration of ca. 12 μM. It is probably dependent on the appropriate environment in the rhizosphere of the host plant in order to persist with sustained nitrogenase activity during cold and dormant periods. Key words: nitrogen fixation, Pseudomonas, psychrotroph, temperature.