Abstract: A strain K19-1 was isolated from maize roots grown in sand of Xinjing Autonomous region. It was identified as Klebsiella planticola. K19-1 could grow on N2-free medium at 40℃ and reduce acetylene and 15N2 at 40℃. The nifH promoter: lacZ fusion was expressed in K19-1 at 40℃. NH4+ did not inhibit Nase activity but repressed the expression of nifH-lacZ fusion in K 19-1. K 19-1 could fix nitrogen anaerobically but Nase activity was still not inhibited till 02 concentration was increased to 4 %. The expression of nifH: lacZ fusion in K 19-1 was not repressed by O2.

Key words: Klebsiella planticola, Nase activity