FIG. 1.

(A) Electron micrograph of strain FW-1a, showing a single flagellum. (B) Electron micrograph of strain FW-1a grown in freshwater medium with poorly crystalline Fe(III) oxide as the sole electron acceptor and H₂ as the sole electron donor in early log phase. (C) Thin-section electron micrograph of strain FW-1a in freshwater medium with poorly crystalline Fe(III) oxide in mid-log phase; the electron-dense material attached to the cells surface appears to be poorly crystalline Fe(III) oxide, which is detached from the cells when it is reduced to magnetite. (D) Thin-section electron micrograph of strain FW-1a (in the same medium as in panels B and C) in late log phase, demonstrating a typical gram-negative bacterium.