Gallionella are neutralophilic iron oxidizing bacteria that are typically confined to microaerophilic environments (living in the gradient between oxidized and reducing conditions). The pH of the Tennyson Mine is ~ 8.5. It is probable that Gallionella (and perhaps Leptothrix) generate energy via Fe oxidation. Gallionella can fix CO2 and also utilize fixed carbon (see Hallbeck and Pedersen, 1991, J. General Microbiol. 137, 2657-2661).

Transmission electron microscope (TEM) images of biomineralization of stalks and sheaths associated with iron hydroxide and iron oxyhydroxide mineralization. In many cases, samples were dominated by coated stalks and sheaths and few cells were detected by DAPI staining (DNA stain). However, cells are present in some samples in high abundance.

The following are TEM images: dark areas are mineralized areas. Individual iiron mineral particle size ranges from ~ 2nm to few tens of nanomter. Ball-like shapes are aggregates of much tiner particles. All stalk and sheath material is heavily mineralized.

Low magnification image of Gallionella and Leptothrix stalks and sheaths

Image of Gallionella and Leptothrix material (mineralized) with clusters of Fe(OH)3 and FeOOO

Image of Gallionella and L eptothrix m aterial (mineralized)

Gallionella stalk coated with nanometer-scale Fe(OH)3 and FeOOH aggregates

Nano-scale FeOOH associate d with Gallionella stalk

Higher magnification image of nano-scale FeOOH associated with Gallio nella stalk

To find out more about the form of the iron hydroxide and its recrystallization to goethite, click here