Suppression of mutation on nitrogenase activity in WLY78 with the addition of high levels of molybdate or cystine.

The diazotrophic WLY78 possesses a minimal nitrogen fixation gene cluster consisting of nine genes ( and ). Notably, the gene contained within the gene cluster is also found within gene clusters among diazotrophic cyanobacteria and . 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 of gene in nitrogen fixation is unknown. In this study, we demonstrate that the mutation of WLY78 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 the mutant could not be restored by or completely. In addition, the mutation does not affect nitrate reductase activity of WLY78. Our results demonstrate is 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.