Effect of biostimulation and bioaugmentation on biodegradation of high concentrations of 1,4-dioxane.

1,4-Dioxane is a pervasive and persistent contaminant in numerous aquifers. Although the median concentration in most contaminant plumes is in the microgram per liter range, a subset of sites have contamination in the milligram per liter range. Most prior studies that have examined 1,4-dioxane concentrations in the hundreds of milligrams per liter range have been performed with industrial wastewater. The main objective of this study was to evaluate aerobic biodegradation of 1,4-dioxane in microcosms prepared with soil and groundwater from a site where concentrations range from ~ 1500 mg·L-1 in the source zone, to 450 mg·L-1 at a midpoint of the groundwater plume, and to 6 mg·L-1 at a down-gradient location. Treatments included biostimulation with propane, addition of propane and a propanotrophic enrichment culture (ENV487), and unamended. The highest rates of biodegradation for each location in the plume occurred in the bioaugmented treatments, although indigenous propanotrophs also biodegraded 1,4-dioxane to below 25 µg·L-1. Nutrient additions were required to sustain biodegradation of propane and cometabolism of 1,4-dioxane. Among the unamended treatments, biodegradation of 1,4-dioxane was detected in the mid-gradient microcosms. An isolate was obtained that grows on 1,4-dioxane as a sole source of carbon and energy and identified through whole-genome sequencing as Pseudonocardia dioxivorans BERK-1. In a prior study, the same strain was isolated from an aquifer in the southeastern United States. Monod kinetic parameters for BERK-1 are similar to those for strain CB1190.

Vault packaged enzyme mediated degradation of amino-aromatic energetic compounds.

Amino-aromatic compounds, 2-amino-4-nitrotoluene (ANT), and 2,4-diaminotoluene (DAT) are carcinogens and environmentally persistent pollutants. In this study, we investigated their degradation by natural manganese peroxidase (nMnP) derived from Phanerochaete chrysosporium and recombinant manganese peroxidase packaged in vaults (vMnP). Encapsulation of manganese peroxidase (MnP) in ribonucleoprotein nanoparticle cages, called vaults, was achieved by creating recombinant vaults in yeast Pichia pastoris. Vault packaging increased the stability of MnP by locally sequestering multiple copies of the enzyme. Within 96  h, both vMnP and nMnP catalyzed over 72% removal of ANT in-vitro, which indicates that vault packaging did not limit substrate diffusion. It was observed that vMnP was more efficient than nMnP and P. chrysosporium for the catalysis of target contaminants. Only 57% of ANT was degraded by P. chrysosporium even when MnP activity reached about 480 U L-1 in cultures. At 1.5 U L-1 initial activity, vMnP achieved 38% of ANT and 51% of DAT degradation, whereas even 2.7 times higher activity of nMnP showed insignificant biodegradation of both compounds. These results imply that due to protection by vault cages, vMnP has lower inactivation rates. Thus, it works effectively at lower dosage for a longer duration compared to nMnP without requiring frequent replenishment. Collectively, these results indicate that fungal enzymes packaged in vault nanoparticles are more stable and active, and they would be effective in biodegradation of energetic compounds in industrial processes, waste treatment, and contaminated environments.

Evaluating the effects of gross nitrogen mineralization, immobilization, and nitrification on nitrogen fertilizer availability in soil experimentally contaminated with diesel.

Sandy clay loam soil was contaminated with 5000 mg kg(-1) diesel, and amended with nitrogen (15.98 atom% (15)N) at 0, 250, 500, and 1000 mg kg(-1) to determine gross rates of nitrogen transformations during diesel biodegradation at varying soil water potentials. The observed water potential values were -0.20, -0.47, -0.85, and -1.50 MPa in the 0, 250, 500, and 1000 mg kg(-1) nitrogen treatments respectively. Highest microbial respiration occurred in the lowest nitrogen treatment suggesting an inhibitory osmotic effect from higher rates of nitrogen application. Microbial respiration rates of 185, 169, 131, and 116 mg O(2) kg(-1) soil day(-1) were observed in the 250, 500, control and 1000 mg kg(-1) nitrogen treatments, respectively. Gross nitrification was inversely related to water potential with rates of 0.2, 0.04, and 0.004 mg N kg(-1) soil day(-1) in the 250, 500, and 1000 mg kg(-1) nitrogen treatments, respectively. Reduction in water potential did not inhibit gross nitrogen immobilization or mineralization, with respective immobilization rates of 2.2, 1.8, and 1.8 mg N kg(-1) soil day(-1), and mineralization rates of 0.5, 0.3, and 0.3 mg N kg(-1) soil day(-1) in the 1000, 500, and 250 mg kg(-1) nitrogen treatments, respectively. Based on nitrogen transformation rates, the duration of fertilizer contribution to the inorganic nitrogen pool was estimated at 0.9, 1.9, and 3.2 years in the 250, 500, and 1000 mg kg(-1) nitrogen treatments, respectively. The estimation was conservative as ammonium fixation, gross nitrogen immobilization, and nitrification were considered losses of fertilizer with only gross mineralization of organic nitrogen contributing to the most active portion of the nitrogen pool.