Abstract
The diazotrophic Paenibacillus polymyxa WLY78 possesses a minimal nitrogen fixation gene cluster consisting of nine genes (nifB nifH nifD nifK nifE nifN nifX hesA and nifV). Notably, the hesA gene contained within the nif gene cluster is also found within nif gene clusters among diazotrophic cyanobacteria and Frankia. 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 hesA gene in nitrogen fixation is unknown. In this study, we demonstrate that the hesA mutation of P. polymyxa 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 hesA mutant could not be restored by Klebsiella oxytoca nifQ or Escherichia coli moeB completely. In addition, the hesA mutation does not affect nitrate reductase activity of P. polymyxa WLY78. Our results demonstrate hesA 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.
Highlights
Nitrogenase, nitrate reductase, and a number of other enzymes require molybdenum and sulfur for their activity (Johnson, 1980; Lester & Demoss, 1971; Pienkos, Shah & Brill, 1977; Shah et al, 1984)
A hesA gene is highly conserved in nif gene clusters among diazotrophic Paenibacillus, cyanobacteria and Frankia Paenibacillus polymyxa WLY78 possesses a minimal nif gene cluster consisting of nine genes
Our previous results demonstrated that the recombinant E. coli 78-7 which was generated by introducing the P. polymyxa nif gene cluster into E. coli JM109 could produce active nitrogenase (Wang et al, 2013)
Summary
Nitrogenase, nitrate reductase, and a number of other enzymes require molybdenum and sulfur for their activity (Johnson, 1980; Lester & Demoss, 1971; Pienkos, Shah & Brill, 1977; Shah et al, 1984). Molybdenum and sulfur are found in these molybdoenzymes as parts of low-molecular-weight cofactors (Johnson, 1980; Shah & Brill, 1977). Most biological nitrogen fixation is catalyzed by molybdenum-dependent nitrogenase, which is distributed within bacteria and archaea. This nitrogenase is a two-component enzyme consisting of the Fe and MoFe proteins (Hu & Ribbe, 2011; Rubio & Ludden, 2008). The MoFe protein is an a2β2 heterotetramer (encoded by nifD and nifK) that
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