Lipolytic enzymes are commonly used to produce desired flavors in lipolyzed milkfat (LMF) manufacturing processes. However, the choice of enzyme is critical because it determines the final profile of fatty acids released and the consequent flavor of the product. We previously constructed a metagenomic library from marine sediments, to explore the novel enzymes which have unique properties useful in flavor-enhancing LMF.

Ferric uptake regulator (Fur) plays a key role in the iron homeostasis of prokaryotes, such as bacterial pathogens, but the molecular mechanisms and structural basis of Fur–DNA binding remain incompletely understood. Here, we report high-resolution structures of Magnetospirillum gryphiswaldense MSR-1 Fur in four different states: apo-Fur, holo-Fur, the Fur–feoAB1 operator complex and the Fur–Pseudomonas aeruginosa Fur box complex. Apo-Fur is a transition metal ion-independent dimer whose binding induces profound conformational changes and confers DNA-binding ability. Structural characterization, mutagenesis, biochemistry and in vivo data reveal that Fur recognizes DNA by using a combination of base readout through direct contacts in the major groove and shape readout through recognition of the minor-groove electrostatic potential by lysine. The resulting conformational plasticity enables Fur binding to diverse substrates. Our results provide insights into metal ion activation and substrate recognition by Fur that suggest pathways to engineer magnetotactic bacteria and antipathogenic drugs.

Aims: To establish a criterion for measuring the purity of purified and sterilized magnetosomes from Magnetospirillum gryphiswaldense and to evaluate their toxicity for mouse fibroblasts in vitro. Methods and Results: The purification of magnetosomes involves disrupting bacterial cells with a French Press, washing directly with PBS buffer accompanied by treatment with low power ultrasonication, and using a magnet to collect the magnetosomes. Five characteristic peaks were displayed by Fourier‐transform infrared spectroscopy (FT‐IR), which was used to detect the quality of the purified magnetosomes, at 3273, 2921, 1735, 1645 and 1531 cm⁻¹. The purified magnetosomes showed no evidence of impurities when observed by transmission electron microscopy and energy disperse spectroscopy. The particles could be stored at −20°C after lyophilization and treatment by γ‐rays. Purified and sterilized magnetosomes had no obvious negative effects on the viability of mouse fibroblasts by 3‐(4,5‐dimethylthiazolyl)‐2,5‐diphenyl‐tetrazolium bromide assay. Conclusions: Purified and sterilized magnetosomes were not toxic to mouse fibroblasts in vitro. Significance and Impact of the Study: This study provides methods for evaluating the purity and safety of magnetosomes from M. gryphiswaldense. The magnetosomes have the potential to be used as novel drug or gene carriers for tumour therapy.

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.