High-yield growth and magnetosome formation by Magnetospirillum gryphiswaldense MSR-1 in an oxygen-controlled fermentor supplied solely with air

Abstract

Magnetotactic bacteria are difficult to grow under defined conditions in culture, which has presented a major obstacle to commercial application of magnetosomes. We studied the relationships among the cell growth, magnetosome formation, dissolved oxygen concentration (DO), and the ability to supply oxygen to the cells. Mass culture of Magnetospirillum gryphiswaldense MSR-1 for the production of magnetosomes was established in a 42-L fermentor under the following conditions: (1) sterile air was the sole gas supplied in the fermentor, and DO could be regulated at any level below 10% saturation by cascading the stir rate to DO, (2) to resolve the paradoxical situation that the cell growth requires higher DO whereas magnetosome formation requires low DO below the detectable range of regular oxygen electrode, DO was controlled to optimal level using the change of cell growth rate, rather than reading from the highly sensitive oxygen electrode, as the signal for determining appropriate DO, and (3) timing and rate of supplying the substrates were determined by measuring cell density and Na-lactate concentration. Under these conditions, cell density (OD565) of strain MSR-1 reached 7.24 after 60-h culture in a 42-L fermentor, and cell yield (dry weight) was 2.17 g/L, the highest yield so far being reported. The yield of magnetosomes (dry weight) was 41.7 mg/L and 16.7 mg/L/day, which were 2.8 and 2.7 times higher than the previously reported yields.

Deletion of the ftsZ -Like Gene Results in the Production of Superparamagnetic Magnetite Magnetosomes in Magnetospirillum gryphiswaldense

“…Escherichia coli strains were grown in Luria-Bertani (LB) medium at 37°C. M. gryphiswaldense strains were grown at 30°C in optimized flask medium (OFM) (49). Sterilized ferric citrate was added as the iron source after autoclaving.…”

Semicontinuous Culture of Magnetospirillum gryphiswaldense MSR-1 Cells in an Autofermentor by Nutrient-Balanced and Isosmotic Feeding Strategies

“…A suspension of concentrated bacteria obtained by centrifugation was adsorbed onto a copper grid, washed twice with distilled water, dried, and viewed and recorded using a transmission electron microscope (H-8000; Hitachi, Japan) (10).…”

“…Previous studies have addressed a variety of applications and properties, including enzyme immobilization (5), gene delivery system (16), cell separation (19), drug carriers (11,12), immunoassays (4,14), protein and multisubunit enzyme complexes (7,20), and use of microorganisms per se for mineral recovery (13). Because of the highly restrictive culture conditions for magnetotactic bacteria, in terms of the dissolved oxygen concentration (dO 2 ) (3, 17), nutrients, etc., the yields of both magnetosomes and their host microorganisms under artificial culture tend to be low (10,18). A long-standing research goal of our laboratory is improved large-scale production of cells and magnetosomes.…”

Synthesis, Functionalization, and Design of Magnetic Nanoparticles for Theranostic Applications

“…[283] Sun et al used a fermenter to control the level of dissolved oxygen and after 60 h of culture incubation obtained magnetite yield of 16.7 mg L −1 d −1 . [284] In a similar study performed by Liu et al magnetite yield 55.49 mg L −1 d −1 after 36 h of culture was reported in a condition where the amount of carbon and electron source were decreased. [280] In a different strategy, Silva et al used a statistical-based experimental factorial design to…”