The sample of a low temperature (20–30°C), slightly acidic (pH 6.26)
fluid, obtained from an actively venting chimney at Franklin Seamount
allows physical and chemical constraints to be placed on the types of
iron oxidizing bacteria that should thrive in the vent environment.
shows the redox conditions for common iron bearing compounds together
with favorable environments for the growth of various genera of iron
oxidizing bacteria. Lundgren and Dean noted that iron-rich substrates such as iron carbonates and sulfides nurture Leptothrix and Gallionella under conditions of neutral pH and medium to low f(O2). The bacterial genus Leptothrix produces filamentous sheaths that can become heavily encrusted with hydrated ferric and manganic oxyhydroxides.
sheath is defined as a hollow cylindrical structure made up
predominantly of encrusted iron and possibly manganese oxyhydroxides
that surrounds a chain of cells. It is closely fitting but not in
intimate contact with the cells so the bacterium may move out leaving
behind a preserved cast.  The width, length and rough surface of the described filaments suggest that Leptothrix is the most common genus at the Franklin Seamount vent sites.
The samples from Franklin Seamount contain very little organic carbon (0.18 to 0.94 wt.% Corg, ref. ),
so it is probable that the organisms had died and decomposed, leaving
behind their fossil form. Submersible observations of the chimneys and
shipboard examination of the samples found no indication of
macro-biological activity except for a few worm casts. [4,5] The genus Gallionella is identified at the vent sites by its spirally twisted stalk structure (Figs. 3d and 4e) formed by the rotation of the individual filaments of its apical cells. 
In summary, the morphologies of ferric iron casts suggest that the iron oxidizing bacteria Leptothrix and Gallionella once thrived within the iron oxyhydroxide chimneys at Franklin Seamount. A near neutral pH, low f(O2)
and ferrous iron-rich vent fluid combined with a seawater environment
rich in organic carbon favored the growth of these genera. Recognition
of the casts made by these genera, and specifically the textures of the
manganese and iron, is good evidence that microbially mediated
deposition of iron is occurring at Franklin Seamount.