Browsing by Author "da Silva, Marcio L.B."

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    1,4-Dioxane-degrading consortia can be enriched from uncontaminated soils: prevalence of Mycobacterium and soluble di-iron monooxygenase genes
    (Wiley, 2017) He, Ya; Mathieu, Jacques; da Silva, Marcio L.B.; Li, Mengyan; Alvarez, Pedro J.J.
    Two bacterial consortia were enriched from uncontaminated soil by virtue of their ability to grow on 1,4-dioxane (dioxane) as a sole carbon and energy source. Their specific dioxane degradation rates at 30°C, pH = 7 (i.e. 5.7 to 7.1 g-dioxane per g-protein per day) were comparable to those of two dioxane-metabolizing archetypes: Pseudonocardia dioxanivoransCB1190 and Mycobacterium dioxanotrophicusPH-06. Based on 16S rRNA sequencing, Mycobacterium was the dominant genus. Acetylene inhibition tests suggest that dioxane degradation was mediated by monooxygenases. However, qPCR analyses targeting the tetrahydrofuran/dioxane monooxygenase gene (thmA/dxmA) (which is, to date, the only sequenced dioxane monooxygenase gene) were negative, indicating that other (as yet unknown) catabolic gene(s) were responsible. DNA sequence analyses also showed threefold to sevenfold enrichment of group 5 and group 6 soluble di-iron monooxygenase (SDIMO) genes relative to the original soil samples. Whereas biodegradation of trace levels of dioxane is a common challenge at contaminated sites, both consortia degraded dioxane at low initial concentrations (300 μg l−1) below detectable levels (5 μg l−1) in bioaugmented microcosms prepared with impacted groundwater. Overall, this work shows that dioxane-degrading bacteria (and the associated natural attenuation potential) exist even in some uncontaminated soils, and may be enriched to broaden bioaugmentation options for sites experiencing insufficient dioxane catabolic capacity.
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    Rapid Metabolism of 1,4-Dioxane to below Health Advisory Levels by Thiamine-Amended Rhodococcus ruber Strain 219
    (American Chemical Society, 2021) Simmer, Reid A.; Richards, Patrick M.; Ewald, Jessica M.; Schwarz, Cory; da Silva, Marcio L.B.; Mathieu, Jacques; Alvarez, Pedro J.J.; Schnoor, Jerald L.
    Bioremediation is a promising treatment technology for 1,4-dioxane-contaminated groundwater. However, metabolic dioxane-degrading bacteria identified to date are limited by their slow kinetics and inability to sustain growth at low dioxane concentrations (<100 μg/L). Furthermore, strains may underperform because of missing growth factors, such as amino acids or vitamins. In this work, we reevaluate Rhodococcus ruber strain 219 as a dioxane-degrading strain with bioaugmentation potential. We report rapid growth and metabolic dioxane degradation by R. ruber 219 when supplemented with thiamine (vitamin B1). We also discern that the strain lacks a complete de novo thiamine synthesis pathway, indicating that R. ruber 219 is a probable thiamine auxotroph. However, when supplemented with thiamine, the strain’s Monod kinetics (Ks = 0.015 ± 0.03 μg/L) and exceedingly low Smin (0.49 ± 1.16 μg/L) suggest this strain can maintain growth at very low dioxane concentrations (<100 μg/L). Accordingly, we demonstrate that thiamine-grown R. ruber 219 sustains degradation of dilute dioxane (<100 μg/L) to below health advisory levels. This is the first study to report sustained metabolic dioxane biodegradation to below health advisory levels of 0.35 μg/L. Overall, our findings solidify R. ruber 219 as a promising candidate for bioremediation of dioxane-contaminated groundwater.