The use of cloned nif regulatory elements from Klebsiella pneumoniae to examine nif regulation in Azotobacter vinelandii

Abstract

Regulatory genes controlling nif expression and also nif promoters fused to lacZ from Klebsiella pneumoniae were cloned on wide-host-range plasmids and introduced into Azotobacter vinelandii to compare regulation of nif expression in the two organisms. A low-copy-number plasmid carrying K. pneumoniae nifA corrected an A. vinelandii Nif- regulatory mutation, whereas a plasmid carrying ntrC did not. A high-copy-number plasmid carrying K. pneumoniae nifL eliminated nif expression in K. pneumoniae but not in A. vinelandii K. pneumoniae nifL- and nifF-lacZ fusions were expressed strongly in A. vinelandii and were not repressed by ammonium. A nifH-lacZ fusion was not expressed in any conditions in this background except very weakly when K. pneumoniae nifA was also present. The implications of these findings are discussed.