Characterization of propanotrophic enrichments from agricultural soils capable of 1,4-dioxane biodegradation to sub-μg/L levels

Major challenges to 1,4-dioxane bioremediation concern chemical characteristics that result in migration and persistence, often resulting in large and dilute plumes. In this study, the objectives were to 1) develop propanotrophic enrichment cultures from agricultural soils and determine if they could degrade high and low concentrations of 1,4-dioxane, 2) investigate the feasibility of bioaugmentation for 1,4-dioxane biodegradation in laboratory microcosms and 3) identify dominant propanotrophs and propane monooxygenase genes in the propanotrophic enrichments. Agricultural soils were selected as inocula as they commonly contain microorganisms capable of the biodegradation of a wide range of agricultural chemicals. Propanotrophic enrichment cultures were established from three soils by repeatedly amending propane. Following this, the biodegradation trends for high (3 mg/L) and low (∼200 μg/L) concentrations of 1,4-dioxane were investigated. The experiments also involved bioaugmentation to impacted site sediment microcosms. Prior to their use in bioaugmentation, DNA was extracted from the propanotrophic cultures for shotgun sequencing and analyses with KBase. The easy development of propanotrophic enrichments from agricultural soils suggests a natural abundance of propanotrophs in the soils. Rapid (often <2 weeks) 1,4-dioxane biodegradation was observed in the enrichment cultures at high or low 1,4-dioxane concentrations. 1,4-Dioxane was degraded close to or below the limit of detection (0.46 μg/L) following bioaugmentation. Eighteen propanotrophic metagenome assembled genomes, classifying as Methylibium, Mycobacterium, Rhodococcus opacus, Rhodococcus wratislaviensis and Mesorhizobium, contained full propane monooxygenase operons. Sequences for twenty-two propane monooxygenase operons were retrieved. Sequences for one subunit (prmA) were compared to the closest matches in GenBank. Overall, the developed cultures have potential for use in bioaugmentation to address in situ 1,4-dioxane contamination.