The growth and magnetosome production of the marine magnetotactic vibrio Magnetovibrio blakemorei strain MV-1 were optimized through a statistics-based experimental factorial design. In the optimized growth medium, maximum magnetite yields of 64.3 mg/liter in batch cultures and 26 mg/liter in a bioreactor were obtained.
Magnetotactic bacteria produce intracellular linear chains of nano-sized magnetic organelles called magnetosomes (1). Each magnetosome consists of a magnetite (Fe 3 O 4 ) or greigite (Fe 3 S 4 ) crystal enveloped by a lipid bilayer membrane that contains magnetosome-specific proteins, some of which are responsible for the biomineralization process (1). The biomineralization of magnetosomes is a highly controlled process regulated at the gene level that results in high-purity, single-magnetic-domain particles with defined crystallographic properties and narrow size distributions (1). Because of their unique characteristics, magnetosomes have a great potential for biotechnological applications. In fact, magnetosomes have been used in the immobilization of biological molecules such as enzymes, antibodies, and nucleic acids (2). Moreover, the production of functionalized magnetosomes by the expression of different proteins on or in the magnetosome membrane is among the most promising immobilization approaches for biotechnological use (3) because it combines biologically active macromolecules with the relatively smooth surface of the nano-sized magnetic crystal of the magnetosome. In contrast, the use of nonbiological magnetic carriers with membranes and proteins is a challenge that remains to be met satisfactorily (4).Thus far, biotechnological studies involving magnetosomes have been focused on a very limited number of strains of the genus Magnetospirillum, mostly Magnetospirillum gryphiswaldense strain MSR-1 and Magnetospirillum magneticum strain AMB-1 (5, 6), both of which biomineralize cuboctahedral crystals of magnetite. Little information exists on other cultivated magnetotactic strains like the magnetotactic vibrio Magnetovibrio blakemorei strain MV-1, which produces chains of elongated prismatic magnetosomes (7). Size and shape are important parameters when designing nanoparticles in numerous biomedical applications like drug delivery because the dimensional properties (aspect ratio) of the nanoparticles affect fluid dynamics, retention times, and internalization by cells (8). The magnetosomes of M. blakemorei are a promising alternative in biotechnology applications such as the immobilization of macromolecules because (i) they have an aspect ratio different from that of cuboctahedral magnetosomes, (ii) they intrinsically contain more magnetite than cuboctahedral magnetosomes because of their size (length, ϳ50 nm; width, ϳ40 nm; 40 nm for Magnetospirillum magnetosomes), and (iii) they have a larger surface volume available for immobilization. Thus, M. blakemorei should be an excellent candidate for the development of high-yield cultivation strategies aimed at potential applications of elongat...