Use of NaCN to increase the growth of N₂-fixing bacteria in a model spermosphere mimicked by sucrose and amino acids leached by seeds

The C₂H₂ reduction activity of N₂-fixing bacteria isolated from river sand was examined in a simulated spermosphere in the river sand. The change in the most probable number of N₂ fixers with increasing quantities of CN^- roughly corresponded to that in C₂H₂ reduction activity. However, the most probable number of non-N₂-fixing bacteria decreased except for CN^--tolerant ones. It is therefore speculated that cyanide evolved from seeds during a pregermination period may suppress the growth of general bacteria, but may promote the proliferation of N₂ fixers, thus contributing to the establishment of a spermosphere.