Rapid Metabolism of 1,4-Dioxane to below Health Advisory Levels by Thiamine-Amended Rhodococcus ruber Strain 219

Abstract

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 (K s = 0.015 ± 0.03 μg/L) and exceedingly low S min (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.

Phytoremediation, Bioaugmentation, and the Plant Microbiome

“…We hypothesized that these strains required growth factors (i.e., amino acids or vitamins) not typically included in minimal microbial media. Through another stroke of serendipity, we discovered Rhodococcus ruber strain 219 rapidly grows on and degrades dioxane when supplemented with thiamine (vitamin B1) . This strain had been previously reported only to grow very slowly on dioxane .…”

“…Through another stroke of serendipity, we discovered Rhodococcus ruber strain 219 rapidly grows on and degrades dioxane when supplemented with thiamine (vitamin B1). 60 This strain had been previously reported only to grow very slowly on dioxane. 61 In addition, when grown with thiamine, the strain had the fastest kinetics for dioxane metabolism reported to date.…”

Advances in Remediation Solutions: New Developments and Opportunities in 1,4‐Dioxane Biological Treatment

“…Concentrations of potentially inhibitory constituents in groundwater at some sites, and in higher-concentration treatment streams, may merit consideration on a site-specific basis. In contrast, 1,4-dioxane biodegradation may be enhanced by the addition of oxygen, nutrients (Rolston et al 2019;Miao et al 2021), iron or manganese (Yao et al 2009;Inoue et al 2020), and thiamine (vitamin B1; Simmer et al 2021).…”

Thiamine-Mediated Microbial Interaction between Auxotrophic Rhodococcus ruber ZM07 and Prototrophic Cooperators in the Tetrahydrofuran-Degrading Microbial Community H-1

“…As it is an essential factor for organisms, the effects of thiamine on fermentation ( 15 ), livestock production ( 16 , 17 ), and illness treatment ( 18 , 19 ) have been extensively studied, but there have been few related studies in the field of environmental pollution remediation. To our knowledge, thiamine has been proven to be capable of improving the growth and degradation efficiency of a dioxane-degrading microbe, Rhodococcus ruber strain 219 ( 20 ), which illustrated that adding such essential growth factors can improve the process of microbial remediation. Tetrahydrofuran (THF; a structural analog of dioxane) is a universal solvent widely applied in the chemical and pharmaceutical industries.…”