Production of luciferase-magnetic particle complex by recombinant Magnetospirillum sp AMB-1

Luciferase-bacterial magnetic particle (BMP) complexes were produced by rec ombinant Magnetospirillum sp. AMB-1. We constructed plasmids pKML and pNELM , respectively, by fusing luc to the 5' and 3' terminal of magA, encoding a n integral iron translocating protein situated in the BMP membrane, of AM B -l. In addition, we produced bifunctional active-fusion proteins on BMPs by using a plasmid pAcML. In this plasmid, acetate kinase and luciferase gene s were fused to the N-terminus and the C-terminus of MagA, respectively. Ba cterial magnetic particles isolated from transconjugants for pKML, pNELM an d pAcML exhibited luciferase activity. Bacterial magnetic particles isolate d from transconjugants for pAcML also exhibited acetate kinase activity. Fed-batch culture of pKML transconjugant yielded 2.6 mg BMPs per liter of c ulture, and 95% conversion of iron into magnetite was obtained, at a nitrat e concentration of 1.4 mM. Continuous feeding of iron as ferric quinate sig nificantly enhanced growth and total magnetic production. Final cell concen tration of 1.8 x 10(9) cells/mL and 6 mg per liter of culture was obtained. Magnetite production by fed-batch culture of AMB-1 was about 3 times that obtained by batch culture. There were no significant differences in BMPs yi eld between recombinant AMB-1 cultivated by fed-batch culture and wild type of AM B-l. (C) 2000 John Wiley & Sons, Inc.