FORCE SPECTROSCOPY OF MINERAL-MICROBE BONDS - Life at the Nanoscale: Atomic Force Microscopy of Live Cells - page 300

In many ways, this paper was a proof of concept. was a model Gram-

negative bacterium, and the surface properties of the minerals varied in
terms of their surface charge and hydrophobicity. However, our goal was to
study a mineral-microbe system that was, arguably, far more interesting than
the adhesion of

E. coli

to various minerals. We began to use AFM to study
the interactions between

E. coli

Shewanella , an iron-reducing bacterium, and iron

oxyhydroxide minerals.
Shewanella is a Gram-negative bacterium that can gain energy by shuttling

electrons to not only oxygen but also ferric iron. The real interest in this
creature comes from its novel ability to transfer electrons to Fe(III) that is
within the crystalline structure of minerals like hematite (Fe 2 O 3 ) or goethite
(FeOOH). In other words, this microorganism is able to breathe on solid state
iron minerals when oxygen is absent from a system.
In the late 1980s and early 1990s, a number of other groups proposed
that cytochrome proteins catalyze the terminal transfer of electrons from
the bacterium to Fe(III) in a mineral. 16-20 However, this hypothetical electron
transfer event was challenging to prove because it was essentially hidden
within the small interfacial space between a living cell and mineral.

Table 14.1. Studies of forces and bonds between microorganisms and minerals

Microorganism Mineral or material Ref.

Gram-negative bacteria
Acidithiobacillus ferrooxidans Silicon nitride 21

Burkholderia sp. Muscovite 15

Burkholderia cepecia Silicon nitride 13

Escherichia coli Muscovite, graphite, goethite 14

E. coli Silica or quartz 22, 23

E. coli Silicon nitride or silicon 10, 24, 25

Haemophilus inluenza Silicon nitride or silicon 26

Klebsiella terrigena Silicon nitride 27

Pseudomonas aeruginosa Mica 28

P. aeruginosa Silicon nitride or silicon 28, 29

Pseudomonas putida Silicon nitride 13

Shewanella oneidensis Diaspore, goethite, hematite 30-33

Shewanella putrefaciens Silicon nitride 34

Gram-positive bacteria
Bacillus subtilis Quartz 23

Enterococcus faecalis Glass 35

Staphylococcus aureus Silica 36

S. aureus Silicon nitride 37

Staphylococcus epidermidis Gold 38