Characteristics and optimised fermentation of a novel magnetotactic bacterium, Magnetospirillum sp. ME-1

Magnetotactic bacteria (MTB) can biosynthesise magnetosomes, which have great potential for commercial applications. A new MTB strain, Magnetospirillum sp. ME-1, was isolated and cultivated from freshwater sediments of East Lake (Wuhan, China) using the limiting dilution method. ME-1 had a chain of 17 ± 4 magnetosomes in the form of cubooctahedral crystals with a shape factor of 0.89. ME-1 was closest to Magnetospirillum sp. XM-1 according to 16S rRNA gene sequence similarity. Compared with XM-1, ME-1 possessed an additional copy of mamPA and a larger mamO in magnetosome-specific genes. ME-1 had an intact citric acid cycle, and complete pathway models of ammonium assimilation and dissimilatory nitrate reduction. Potential carbon and nitrogen sources in these pathways were confirmed to be used in ME-1. Adipate was determined to be used in the fermentation medium as a new kind of dicarboxylic acid. The optimised fermentation medium was determined by orthogonal tests. The large-scale production of magnetosomes was achieved and the magnetosome yield (wet weight) reached 120 mg L-1 by fed-batch cultivation of ME-1 at 49 h in a 10-L fermenter with the optimised fermentation medium. This study may provide insights into the isolation and cultivation of other new MTB strains and the production of magnetosomes.