Environmental Engineering Reference
In-Depth Information
SHEWANELLA : NOVEL STRATEGIES FOR
ANAEROBIC RESPIRATION
Thomas J. DiChristina, David J. Bates, Justin L. Burns, Jason R. Dale, Amanda
N. Payne
Georgia Institute of Technology, 311 Ferst Drive, Atlanta, Georgia 30332, USA
Abstract
Metal-reducing members of the genus Shewanella are important components of
the microbial community residing in redox-stratified freshwater and marine envi-
ronments. Metal-reducing gram-negative bacteria such as Shewanella , however,
are presented with a unique physiological challenge: they are required to respire
anaerobically on terminal electron acceptors which are either highly insoluble
(Fe(III)- and Mn(IV)-oxides) and reduced to soluble end-products or highly
soluble (U(VI) and Tc(VII)) and reduced to insoluble end-products. To over-
come physiological problems associated with metal solubility, metal-respiring
Shewanella are postulated to employ a variety of novel respiratory strategies
not found in other gram-negative bacteria which respire on soluble electron ac-
ceptors such as O 2 ,NO 3 and SO 4 . The following chapter highlights the latest
findings on the molecular mechanism of Fe(III), U(VI) and Tc(VII) reduction by
Shewanella , with particular emphasis on electron transport chain physiology.
Keywords: Shewanella , metal reduction, anaerobic respiration, iron, uranium, technetium,
dissolution, precipitation.
Although members of the genus Shewanella were first isolated nearly 75
years ago from spoiling dairy products and fish [78, 91], only recently have
they received attention as important members of natural microbial communities.
Shewanella have been isolated from a variety of marine, freshwater and terres-
trial subsurface environments, including marine basins and sediments (Black
Sea, Baltic Sea, Mississippi and Amazon River deltas, North Sea, Antarctic and
Arctic Oceans, Mariana Trench at a depth of 11,000 m), freshwater rivers, lakes
and sediments (Oneida Lake, NY, Lake Michigan), corroding oil pipelines (Al-
berta, Canada) and uranium-contaminated subsurface aquifers (New Mexico)
[87]. Shewanella have also recently been detected in the surface waters of the
Sargasso Sea [88], a finding that dramatically expands the normal range of
Shewanella habitats.
Shewanella are members of the gamma subdivision of the Proteobacteria
[15, 87]. Shewanella display remarkable respiratory versatility as they are
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