Mass culture of magnetic bacteria and their application to flow type immunoassays

Isolated helical magnetotactic bacteria were cultured in a medium containing succinate, nitrate, and ferric malate as carbon, nitrogen, and iron sources, respectively. The magnetotactic bacteria could grow aerobically. The cells which grew aerobically had oxidase activity. An initial inoculum of 10⁵ cells/ml was used. Stationary phase was reached 1.4×10⁹ cells/ml after 4-5 days growth. When the cells were disrupted using ultrasonication, 2.6-mg bacterial magnetites were obtained from a 1-l culture of magnetotactic bacteria. The detection of mouse IgG was carried out using FITC (fluorescein-isothiocyanate) conjugated anti-mouse-IgG immobilized on bacterial magnetites and a flow injection system with a fluorescence spectrophotometer. Relative fluorescence intensity correlated linearly with the concentration of mouse IgG in the range 0.5-100 ng/ml, and the measurements were established within 2 min using this system