Suppression ofhesAmutation on nitrogenase activity inPaenibacillus polymyxaWLY78 with the addition of high levels of molybdate or cystine

Abstract

The diazotrophicPaenibacillus polymyxaWLY78 possesses a minimal nitrogen fixation gene cluster consisting of nine genes (nifB nifH nifD nifK nifE nifN nifX hesAandnifV). Notably, thehesAgene contained within thenifgene cluster is also found withinnifgene clusters among diazotrophic cyanobacteria andFrankia. The predicted product HesA is a member of the ThiF-MoeB-HesA family containing an N-terminal nucleotide binding domain and a C-terminal MoeZ/MoeB-like domain. However, the function ofhesAgene in nitrogen fixation is unknown. In this study, we demonstrate that thehesAmutation ofP. polymyxaWLY78 leads to nearly complete loss of nitrogenase activity. The effect of the mutation can be partially suppressed by the addition of high levels of molybdate or cystine. However, the nitrogenase activity of thehesAmutant could not be restored byKlebsiella oxytoca nifQorEscherichia coli moeBcompletely. In addition, thehesAmutation does not affect nitrate reductase activity ofP. polymyxaWLY78. Our results demonstratehesAis a novel gene specially required for nitrogen fixation and its role is related to introduction of S and Mo into the FeMo-co of nitrogenase.