Kourtev, P.S., Konopka, A. and Nakatsu,
C.H. (2006). Responses of the anaerobic bacterial community to
the addition of organic C in chromium(VI)- and iron(III)-amended
microcosms Appl. Environ. Microbiol., 72: 628-637.
Chromium (VI) is toxic to microorganisms and can inhibit the
biodegradation of organic pollutants in contaminated soils. We
used microcosms amended with either glucose or protein (to drive
bacterial community change) and Fe(III) (to stimulate
iron-reducing bacteria) to study the effect of various
concentrations of Cr(VI) on anaerobic bacterial
communities. Microcosms were destructively sampled based on
microbial activity (measured as evolution of CO2) and
analyzed for the following: (i) dominant bacterial community by
PCR-denaturing gradient gel electrophoresis (DGGE) of the 16S rRNA
gene; (ii) culturable Cr-resistant bacteria; and (iii) enrichment
of iron-reducing bacteria of the Geobacteraceae family by
real-time PCR. The addition of organic C stimulated the activities
of anaerobic communities. Cr(VI) amendment resulted in lower rates
of CO2, production in glucose microcosms and a slow
mineralization phase in protein-amended microcosms. Glucose and
protein amendments selected for different bacterial
communities. This selection was modified by the addition of
Cr(VI), since some DGGE bands were intensified and new bands
appeared in Cr(VI)-amended microcosms. A second dose of Cr(VI),
added after the onset of activity, had a strong inhibitory effect
when higher levels of Cr were added, indicating that the
developing Cr-resistant communities had a relatively low tolerance
threshold. Most of the isolated Cr-resistant bacteria were closely
related to previously studied Cr-resistant anaerobes, such as
Pantoea, Pseudomonas, and Enterobacter
species. Geobacteraceae were not enriched during the
incubation. The studied Cr(VI)-contaminated soil contained a
viable anaerobic bacterial community; however, Cr(VI) altered its
composition, which could affect the soil biodegradation potential.
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