Chemistry Reference
In-Depth Information
FIGURE 7.2
Amphiphilic marine siderophores, including marinobactins, aquachelins, amphibactins, ochrobactins, and synechobactins.
(Adapted from
Vraspir & Butler, 2009
. NIH Public Access.)
oxygen, and a number of organic compounds to the reduction of Fe(III) or Mn(IV). This dissimilatory
3
Fe(III) and
Mn(IV) reduction influences the organic as well as the inorganic geochemistry of anaerobic aquatic sediments and
groundwater. Microorganisms capable of conserving energy from metal reduction are widely dispersed
throughout the Bacteria and Archae kingdoms. However, they face the dilemma that the most prevalent forms of
Fe(III) or Mn(IV) in the majority of environments are the insoluble oxides. Electron transfer from the inner
membrane to the outer membrane in Geobacter and Shewanella species appears to involve an electron transport
chain of inner membrane, periplasmic, and outer membrane multihaem c-type cytochromes (
Fig. 7.4
)
. In She-
wanella oneidensis, multihaem decahaem c-Cyts CymA and MtrA are believed to transfer electrons from the inner
membrane quinone/quinol pool through the periplasm to the outer membrane. The c-Cyts MtrC and OmcA at the
extracellular face of the outer membrane can directly reduce solid metal oxides. Likewise, outer membrane
multihaem c-Cyts OmcE and OmcS of Geobacter sulfurreducens are thought to transfer electrons from outer
membrane to type IV pili that are hypothesised to relay the electrons to solid metal (hydr)oxides. These multihaem
c-Cyts play critical roles in S. oneidensis and G. sulfurreducens-mediated dissimilatory reduction of solid metal
oxides by facilitating ET across the bacterial cell envelope.
3. A word which is not recognised in English or American dictionaries: it clearly was invented to indicate the opposite of assimilation -
nothing to do with dissimulation!
