Nod Bj-V (C18:1, MeFuc) production by Bradyrhizobium japonicum (USDA110, 532C) at suboptimal growth temperatures

Nod factors (Lipo-chitooligosaccharides, or LCOs) act as bacteria-to-plant signal molecules that modulate early events of the Bradyrhizobium-soybean symbiosis. It is known that low root zone temperature inhibits the early stages of this symbiosis; however, the effect of low soil temperature on bacteria-to-plant signaling is largely uninvestigated. We evaluated the effect of low growth temperatures on the production kinetics of Nod factor (LCO) by B. japonicum. Two strains of B. japonicum, 532C and USDA110, were tested for ability to synthesize Nod Bj-V (C(18:1), MeFuc) at three growth temperatures (15, 17 and 28 degrees C). The greatest amounts of the major Nod factor, Nod Bj-V (C(18:1), MeFuc), were produced at 28 degrees C for both strains. At 17 and 15 degrees C, the Nod factor production efficiency, per cell, of B. japonicum 532C and USDA110 was markedly decreased with the lowest Nod factor concentration per cell occurring at 15 degrees C. Strain 532C was more efficient at Nod factor production per cell than strain USDA 110 at all growth temperatures. The biological activity of the extracted Nod factor was unaffected by culture temperature. This study constitutes the first demonstration of reduced Nod factor production efficiency (per cell production) under reduced temperatures, suggesting another way that lower temperatures inhibit establishment of the soybean N(2) fixing symbiosis.