Semicontinuous culture of Magnetospirillum gryphiswaldense MSR-1 cells in an autofermentor by nutrient-balanced and isosmotic feeding strategies

An improved strategy was developed for the high-density culture of Magnetospirillum gryphiswaldense strain MSR-1 and large-scale magnetosome production in both 7.5- and 42-liter autofermentors. By using a nutrient-balanced feeding strategy and the replacement of carbon and nitrogen sources to reduce accumulation of Na(+) and Cl(-) ions, we reduced the factors that tend to inhibit cell growth, particularly the increase of osmotic potential. Semicontinuous culture was thereby achieved in the autofermentor for the first time. When the cells were harvested at 36 and 73 h, magnetosome yields (dry weight) as high as 168.3 and 83.5 mg/liter/day, respectively, were achieved. These values were, respectively, approximately 10 and 5 times higher than the yields achieved in previous studies and represent a significant improvement in magnetosome production efficiency.