In situ measurement of Fe(III) reduction activity of Geobacter pelophilus by simultaneous in situ RT-PCR and XPS analysis
Andrew L. Neal a, Lani K. Clough b, Todd D. Perkins
b, Brenda J. Little c, Timothy S. Magnuson
b
a Department of Microbiology and Savannah River
Ecology Laboratory, University of Georgia, Athens, GA 30602, USA
b Department of Biological Sciences, Idaho State University,
Pocatello, ID 83204, USA
C Naval Research Laboratory, Stennis Space Center, MS 39529-5494
Huntsville, AL, USA
Received.7 December 2002; received in revised form 12 August 2003; accepted
1 March 2004
First published online 16 April 2004
Abstract
Geobacter pelophilus is capable of dissimilatory Fe(III)-reduction
on solid phase Fe(III)-oxides by means of surface attachment and direct
electron transport to Fe(III), in part mediated by outer membrane c-type
cytochromes. A study was undertaken to characterize surface colonization
patterns, gene expression, and mineral transformation by this organism.
The gene fer A (Geobacter sulfurreducens outer membrane Fe(III)
reductase cytochrome c) was used as a target for PCR based molecular detection
methods for visualizing G. pelophilus surface colonization. Protein
extracts were prepared from solid-phase cultures, and cytochrome c
content assessed. Mineral transformations were followed by X-ray photoelectron
spectroscopy (XPS). Results of in situ (IS) R T -PCR ex- periments demonstrate
that G. pelophilus attaches and grows at ferrihydrite mineral
surfaces. Fluorescently-labeled cells were observed after IS-RT-PCR experiments,
suggesting that G. pelophilus contains a cytochrome c sequence
similar to fer A in G. sulfurreducens which is expressed
in the presence of ferrihydrite. Protein extracts possessed high mass
c-type cytochromes of similar size to those found in G. sulfurreducens.
In addition, unique high-mass c-type cytochromes were also detected. XPS
analysis demonstrated mineral transformation to occur, mediated by the
surface associated population. This study demonstrates that G. pelophilus
attaches to Fe(III)-oxide surfaces, reduces the Fe (III) oxides at the
surface, produces c-type cytochromes under these growth conditions, and
expresses cytochrome c-encoding genes as measured by in situ molecular
detection techniques.
Keywords: Iron respiring bacterium; Gene detection; Surface attachment;
Mineral transformation; Geobacteraceae
SREL Reprint #2770
Neal, A. L., L. K. Clough, T. D. Perkins, B. J. Little and T. S. Magnuson. 2004. In situ measurement of Fe(III) reduction activity of Geobacter pelophilus by simultaneous in situ RT-PCR and XPS analysis. FEMS Microbiology Ecology 49:163-169.
