Synthesis of nitrogenase by Paenibacillus sabinae T27 in presence of high levels of ammonia during anaerobic fermentation.

Biological nitrogen fixation is usually inhibited by fixed nitrogen. Paenibacillus sabinae T27, a Gram-positive, spore-forming diazotroph, possesses high nitrogenase activity and has 3 copies of nifH (nifH, nifH2, nifH3), a copy of nifDK, and multiple nifHDK-like genes. In this study, we found that P. sabinae T27 showed nitrogenase activities not only in low (0-3 mM) concentrations of NH4+ but also in high (30-300 mM) concentrations of NH4+, no matter whether this bacterium was grown in a flask or in a fermenter on scale cultivation. qRT-PCR and western blotting analyses supported that Fe protein and MoFe protein were synthesized under both low (0-3 mM) and high (30-300 mM) concentrations of NH4+. Liquid chromatography-mass spectrometry (LC-MS) analysis revealed that MoFe protein was encoded by nifDK and Fe protein was encoded by both nifH and nifH2. The cross-reaction suggested the purified Fe and MoFe components from P. sabinae T27 grown in both nitrogen-limited and nitrogen-excess conditions were active. This is the first time to report that diazotrophs show nitrogenase activity in presence of high (30-300 mM) concentrations of NH4+. Our study will provide a clue for studying the mechanisms of nitrogen fixation in presence of the high concentration of NH4+. KEY POINTS: • P. sabinae T27 can synthesize active nitrogenase in presence of high levels of ammonia. •Fe and MoFe proteins of nitrogenase purified in absence of ammonia are the same as those purified from the high concentration of ammonia. • Fe protein is encoded by nifH and nifH2, and MoFe protein is encoded by nifDK.