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

摘要

In order to study the establishment of a spermosphere, the C2H2reduction activity of N2-fixing bacteria isolated from river sand was examined in a simulated spermosphere in the river sand which contained sucrose, an amino acid mixture, and CN-released from plant seeds. The sand incubated with 10-10to 10-9mol CN-30 g sand-1exhibited higher C2H2reduction activity than that without CN-. The change in the most probable number of N2fixers with increasing quantities of CN-roughly corresponded to that in C2H2reduction activity. However, the most probable number of non-N2-fixing bacteria decreased except for CN--tolerant ones. Both C2H2reduction activity and proliferation of the N2fixers isolated on a modified Burk's medium were almost similar to those in the bacteria in the sand. In contrast, the proliferation of some nonfixers decreased with an increasing CN-concentration. C2H2reduction activity of N2fixers cultured in combination with non-fixers exhibited a clear peak at 10-7MCN-as for C2H2reduction activity in the sand. We therefore speculate that cyanide evolved from seeds during a pregermination period may suppress the growth of general bacteria, but may promote the proliferation of N2fixers, thus contributing to the establishment of a spermosphere.