Inhibition of Nitrate Reduction by Chromium(VI) in Anaerobic Soil Microcosms

Abstract

Chromium is often found as a cocontaminant at sites polluted with organic compounds. For nitrate-respiring microbes, Cr(VI) may be not only directly toxic but may also specifically interfere with N reduction. In soil microcosms amended with organic electron donors, Cr(VI), and nitrate, bacteria oxidized added carbon, but relatively low doses of Cr(VI) caused a lag and then lower rates of CO 2 accumulation. Cr(VI) strongly inhibited nitrate reduction; it occurred only after soluble Cr(VI) could not be detected. However, Cr(VI) additions did not eliminate Cr-sensitive populations; after a second dose of Cr(VI), bacterial activity was strongly inhibited. Differences in microbial community composition (assayed by PCR-denaturing gradient gel electrophoresis) driven by different organic substrates (glucose and protein) were smaller than when other electron acceptors had been used. However, the selection of bacterial phylotypes was modified by Cr(VI). Nine isolated clades of facultatively anaerobic Cr(VI)-resistant bacteria were closely related to cultivated members of the phylum Actinobacteria or Firmicutes. In Bacillus cereus GNCR-4, the nature of the electron donor (fermentable or nonfermentable) affected Cr(VI) resistance level and anaerobic nitrate metabolism. Our results indicate that carbon utilization and nitrate reduction in these soils were contingent upon the reduction of added Cr(VI). The amount of Cr(VI) required to inhibit nitrate reduction was 10-fold less than for aerobic catabolism of the same organic substrate. We speculate that the resistance level of a microbial process is directly related to the diversity of microbes capable of conducting it.

Impact of copper on the diversity, abundance and transcription of nitrite and nitrous oxide reductase genes in an urban European estuary

“…7); the detrimental effect of Cu occurred through a drastic reduction of denitrifier cells and the transcript diversity of the different genes involved. This subtractive effect by metals on microbial community composition has been identified in other studies (Müller et al , 2001; Holtan‐Hartwig et al , 2002; Kourtev et al , 2009). In our study, because most of the denitrifier community were sensitive to Cu, their contribution to the community was lost, and the ability to denitrify was affected even at the 4 μg Cu g −1 wet wt sediment concentration and was completely disrupted after the addition of 60 μg Cu g −1 wet wt sediment.…”

“…However, the question of whether metal contaminants can directly affect essential biogeochemical processes at the genomic and transcriptional levels, i.e. at the ‘preprotein’ level, has rarely been considered (Kourtev et al , 2009). In the present study, we examine how one major metal pollutant, copper (Cu), can affect denitrification activity with regard to the diversity of genotypes and transcripts of nitrite ( nirS and nirK ) and nitrous oxide reductase ( nosZ ) genes in an estuarine microbial community.…”

Metabolic and genomic analysis elucidates strain-level variation inMicrobacterium spp.isolated from chromate contaminated sediment

“…Bill Jervis from the Indiana Department of Transport provided site access (no permit was required) and the project did not involve endangered or protected species. Bacterial strains were isolated from the contaminated soil as described in Kourtev, Nakatsu & Konopka (2009) . Briefly, isolates were enriched on 50% trypic soy agar (TSA) and 0.25 mM Cr(VI).…”

“…Chromium is the second most common contaminant at US Department of Energy sites, and without proper remediation could persist at dangerous levels well past 1,000 years from now ( Okrent & Xing, 1993 ; Riley, Zachara & Wobber, 1992 ). Further, chromium is of particular concern because of its solubility in water and potential risk to drinking water; as well as the potential to inhibit the natural microbial communities engaged in the bioremediation of other pollutants ( Bååth, 1989 ; Gough et al, 2008 ; Gough & Stahl, 2011 ; Kourtev, Nakatsu & Konopka, 2009 ; Nakatsu et al, 2005 ; Said & Lewis, 1991 ). As such, chromium contamination of soil and water poses risks to the United States and other industrial nations without proper remediation ( Ackerley et al, 2004a ; Beller et al, 2013 ; Cheng, Holman & Lin, 2012 ; He et al, 2010 ).…”

Peer Review #1 of "Metabolic and genomic analysis elucidates strain-level variation in Microbacterium spp. isolated from chromate contaminated sediment (v0.2)"

“…Bill Jervis from the Indiana Department of Transport provided site access (no permit was required) and the project did not involve endangered or protected species. Bacterial strains were isolated from the contaminated soil as described in Kourtev et al (Kourtev et al 2009).…”