Using synthetic biology to increase nitrogenase activity

BACKGROUND: Nitrogen fixation has been established in protokaryotic model Escherichia coli by transferring a minimal nif gene cluster composed of 9 genes (nifB, nifH, nifD, nifK, nifE, nifN, nifX, hesA and nifV) from Paenibacillus sp. WLY78. However, the nitrogenase activity in the recombinant E. coli 78-7 is only 10 % of that observed in wild-type Paenibacillus. Thus, it is necessary to increase nitrogenase activity through synthetic biology. RESULTS: In order to increase nitrogenase activity in heterologous host, a total of 28 selected genes from Paenibacillus sp. WLY78 and Klebsiella oxytoca were placed under the control of Paenibacillus nif promoter in two different vectors and then they are separately or combinationally transferred to the recombinant E. coli 78-7. Our results demonstrate that Paenibacillus suf operon (Fe–S cluster assembly) and the potential electron transport genes pfoAB, fldA and fer can increase nitrogenase activity. Also, K. oxytocanifSU (Fe–S cluster assembly) and nifFJ (electron transport specific for nitrogenase) can increase nitrogenase activity. Especially, the combined assembly of the potential Paenibacillus electron transporter genes (pfoABfldA) with K. oxytocanifSU recovers 50.1 % of wild-type (Paenibacillus) activity. However, K. oxytocanifWZM and nifQ can not increase activity. CONCLUSION: The combined assembly of the potential Paenibacillus electron transporter genes (pfoABfldA) with K. oxytocanifSU recovers 50.1 % of wild-type (Paenibacillus) activity in the recombinant E. coli 78-7. Our results will provide valuable insights for the enhancement of nitrogenase activity in heterogeneous host and will provide guidance for engineering cereal plants with minimal nif genes. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12934-016-0442-6) contains supplementary material, which is available to authorized users.