12 research outputs found
Impact of Ammonium on Syntrophic Organohalide-Respiring and Fermenting Microbial Communities
Citation: Delgado, A. G., Fajardo-Williams, D., Kegerreis, K. L., Parameswaran, P., & Krajmalnik-Brown, R. (2016). Impact of Ammonium on Syntrophic Organohalide-Respiring and Fermenting Microbial Communities. Msphere, 1(2), 10. doi:10.1128/mSphere.00053-16Syntrophic interactions between organohalide-respiring and fermentative microorganisms are critical for effective bioremediation of halogenated compounds. This work investigated the effect of ammonium concentration (up to 4 g liter(-1) NH4+-N) on trichloroethene-reducing Dehalococcoides mccartyi and Geobacteraceae in microbial communities fed lactate and methanol. We found that production of ethene by D. mccartyi occurred in mineral medium containing = 1 g liter(-1) NH4+-N, organohalide-respiring dynamics shifted from D. mccartyi and Geobacteraceae to mainly D. mccartyi. An increasing concentration of ammonium was coupled to lower metabolic rates, longer lag times, and lower gene abundances for all microbial processes studied. The methanol fermentation pathway to acetate and H-2 was conserved, regardless of the ammonium concentration provided. However, lactate fermentation shifted from propionic to acetogenic at concentrations of >= 2 g liter(-1) NH4+-N. Our study findings strongly support a tolerance of D. mccartyi to high ammonium concentrations, highlighting the feasibility of organohalide respiration in ammonium-contaminated subsurface environments. IMPORTANCE Contamination with ammonium and chlorinated solvents has been reported in numerous subsurface environments, and these chemicals bring significant challenges for in situ bioremediation. Dehalococcoides mccartyi is able to reduce the chlorinated solvent trichloroethene to the nontoxic end product ethene. Fermentative bacteria are of central importance for organohalide respiration and bioremediation to provide D. mccartyi with H2, their electron donor, acetate, their carbon source, and other micronutrients. In this study, we found that high concentrations of ammonium negatively correlated with rates of trichloroethene reductive dehalogenation and fermentation. However, detoxification of trichloroethene to nontoxic ethene occurred even at ammonium concentrations typical of those found in animal waste (up to >= 2 g liter(-1) NH4+-N). To date, hundreds of subsurface environments have been bioremediated through the unique metabolic capability of D. mccartyi. These findings extend our knowledge of D. mccartyi and provide insight for bioremediation of sites contaminated with chlorinated solvents and ammonium
Role of bicarbonate as a pH buffer and electron sink in microbial dechlorination of chloroethenes
<p>Abstract</p> <p>Background</p> <p>Buffering to achieve pH control is crucial for successful trichloroethene (TCE) anaerobic bioremediation. Bicarbonate (HCO<sub>3</sub><sup>−</sup>) is the natural buffer in groundwater and the buffer of choice in the laboratory and at contaminated sites undergoing biological treatment with organohalide respiring microorganisms. However, HCO<sub>3</sub><sup>−</sup> also serves as the electron acceptor for hydrogenotrophic methanogens and hydrogenotrophic homoacetogens, two microbial groups competing with organohalide respirers for hydrogen (H<sub>2</sub>). We studied the effect of HCO<sub>3</sub><sup>−</sup> as a buffering agent and the effect of HCO<sub>3</sub><sup>−</sup>-consuming reactions in a range of concentrations (2.5-30 mM) with an initial pH of 7.5 in H<sub>2</sub>-fed TCE reductively dechlorinating communities containing <it>Dehalococcoides</it>, hydrogenotrophic methanogens, and hydrogenotrophic homoacetogens.</p> <p>Results</p> <p>Rate differences in TCE dechlorination were observed as a result of added varying HCO<sub>3</sub><sup>−</sup> concentrations due to H<sub>2</sub>-fed electrons channeled towards methanogenesis and homoacetogenesis and pH increases (up to 8.7) from biological HCO<sub>3</sub><sup>−</sup> consumption. Significantly faster dechlorination rates were noted at all HCO<sub>3</sub><sup>−</sup> concentrations tested when the pH buffering was improved by providing 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) as an additional buffer. Electron balances and quantitative PCR revealed that methanogenesis was the main electron sink when the initial HCO<sub>3</sub><sup>−</sup> concentrations were 2.5 and 5 mM, while homoacetogenesis was the dominant process and sink when 10 and 30 mM HCO<sub>3</sub><sup>−</sup> were provided initially.</p> <p>Conclusions</p> <p>Our study reveals that HCO<sub>3</sub><sup>−</sup> is an important variable for bioremediation of chloroethenes as it has a prominent role as an electron acceptor for methanogenesis and homoacetogenesis. It also illustrates the changes in rates and extent of reductive dechlorination resulting from the combined effect of electron donor competition stimulated by HCO<sub>3</sub><sup>−</sup> and the changes in pH exerted by methanogens and homoacetogens.</p
Coupling Bioflocculation of <i>Dehalococcoides mccartyi</i> to High-Rate Reductive Dehalogenation of Chlorinated Ethenes
Continuous
bioreactors operated at low hydraulic retention times
have rarely been explored for reductive dehalogenation of chlorinated
ethenes. The inability to consistently develop such bioreactors affects
the way growth approaches for <i>Dehalococcoides mccartyi</i> bioaugmentation cultures are envisioned. It also affects interpretation
of results from in situ continuous treatment processes. We report
bioreactor performance and dehalogenation kinetics of a <i>D.
mccartyi</i>-containing consortium in an upflow bioreactor. When
fed synthetic groundwater at 11–3.6 h HRT, the upflow bioreactor
removed >99.7% of the influent trichloroethene (1.5–2.8
mM)
and produced ethene as the main product. A trichloroethene removal
rate of 98.51 ± 0.05 me<sup>–</sup> equiv L<sup>–1</sup> d<sup>–1</sup> was achieved at 3.6 h HRT. <i>D. mccartyi</i> cell densities were 10<sup>13</sup> and 10<sup>12</sup> 16S rRNA
gene copies L<sup>–1</sup> in the bioflocs and planktonic culture,
respectively. When challenged with a feed of natural groundwater containing
various competing electron acceptors and 0.3–0.4 mM trichloroethene,
trichloroethene removal was sustained at >99.6%. Electron micrographs
revealed that <i>D. mccartyi</i> were abundant within the
bioflocs, not only in multispecies structures, but also as self-aggregated
microcolonies. This study provides fundamental evidence toward the
feasibility of upflow bioreactors containing <i>D. mccartyi</i> as high-density culture production tools or as a high-rate, real-time
remediation biotechnology
Enumeration of <i>Dehalococcoides mccartyi</i> in enrichment cultures.
<p>qPCR tracking <i>Dehalococcoides</i> 16S rRNA genes and their reductive dehalogenase genes, <i>tceA</i>, <i>vcrA</i>, and <i>bvcA</i> in the enrichment cultures after three consecutive additions of 0.5 mmol L<sup>−1</sup> TCE. The plot is representative of triplicate cultures and the error bars show standard deviations of triplicate qPCR reactions.</p
Biostimulation of chlorinated ethene-respiring communities containing <i>Dehalococcoides</i>.
<p>Dechlorination of TCE in microcosms (left panels), first transfers from microcosms (middle panels), and enriched soil/sediment-free cultures (right panels). The microcosms (left panels) were setup with (A) uncontaminated garden soil, (B) uncontaminated mangrove sediment, and (C) PCE-contaminated groundwater sediment. A total of 26 microcosms were established. (A)–(B) (left panels) Cuzdrioara and Carolina microcosm replicates exhibited the same pattern for reductive dechlorination product formation and one replicate is shown. Eight Parris Island replicate microcosms from different core depths formed VC and ethene within 30 days after microcosms were established. (C) (left panel) One representative VC and ethene-producing microcosm is presented. The dashed arrows represent an additional transfer not shown. The time-course experiments from the right panels (A–C) are from the third consecutive addition of 0.5 mmol L<sup>−1</sup> TCE. The error bars in the right panels show standard deviation of triplicate cultures. Note the time scale differences between left, middle, and right panels.</p
Characterization of <i>Dehalococcoides mccartyi</i>-containing cultures enriched in this study.
a<p>Rates calculated between two consecutive sampling points. The transient rates were highest for all cultures on the third addition of 1 mmol L<sup>−1</sup> TCE.</p>b<p>Conversion times reported from independent experiments for the third consecutive addition of TCE.</p>c<p>Final densities after three consecutive additions of TCE.</p>d<p>Yields were calculated from the change in the 16S rRNA gene copies measured by qPCR divided by the change in concentration of TCE reduced to ethene.</p
Bacterial composition at the class level as determined by 454 pyrosequencing of the V2-V3 region of the 16S rRNA gene.
<p>The outer pie charts (A–C) represent the relative abundance of select classes in the Cuzdrioara uncontaminated soil, (B) Carolina uncontaminated sediment, and (C) Parris Island contaminated sediment. The inner pie charts (A'–C') show the five most abundant classes in the respective soil/sediment-free enrichment cultures, ZARA-10, LINA-09, and ISLA-08. The classified taxa presented contributed to at least 1% of the total relative abundance and are organized in alphabetical order.</p
Environmental inocula and enrichment conditions of chlorinated ethene-dechlorinating cultures.
<p>Enrichment originating <i>Dehalococcoides mccartyi</i> strain <sup>a</sup>195, <sup>b</sup>BAV1, <sup>c</sup>VS, and <sup>d</sup>FL2.</p
Alpha and beta microbial diversity analyses.
<p>(A)–(C) Rarefaction plots for PD Whole Tree measurements from the 454 analysis using trimmed, equal sequencing depth OTUs (1,486) per sample. (D) Weighted UNIFRAC distance calculated after trimming the samples to equal sequence depth in QIIME. The PCoA plot was generated by grouping the samples into two categories (soils/sediments vs. enrichment cultures). The color blue corresponds to the soil/sediment samples, while green corresponds to the soil/sediment-free enrichment cultures.</p
Bioaugmentation of microcosms with their respective enrichment cultures.
<p>Dechlorination of TCE in (A) in Cuzdrioara soil microcosms bioaugmentated with ZARA-10 enrichment culture and in (B) Carolina sediment microcosms bioaugmented with LINA-09 culture. The inoculum used for these experiments was 1% vol/vol.</p