Infiltration of Sulfate to Enhance Sulfate Reduction of Petroleum Hydrocarbons

The lack of sufficient electron acceptors, particularly sulfate, can limit the rate of biodegradation of petroleum hydrocarbons (PHCs). Hence there is a growing interest by remediation practitioners to deliver sulfate to a PHC impacted saturated zone to enhance biodegradation. When shallow contamination is present in a relatively permeable aquifer and site constraints allow, a cost-effective approach is to apply sulfate on the ground surface. In this investigation a pilot-scale experiment was conducted to increase our understanding of the delivery of sulfate using a surface-based method and the resulting impact on a shallow PHC contaminated aquifer. A surficial infiltration pond positioned on the ground surface above a well-characterized residual PHC source zone was used to control sulfate dosing. A high-resolution network near the infiltration pond and downgradient of the source zone was employed to monitor relevant geochemical indicators and PHC concentrations. Compound specific isotope analysis (CSIA) was used to identify biodegradation patterns and to investigate the occurrence of microbial sulfate reduction. Selected metabolites and reverse-transcriptase quantitative polymerase chain reaction analyses of expressed biodegradation genes (as mRNA) were also used to characterize the response of indigenous microorganisms (especially sulfate reducing bacteria) to the added sulfate. Three sulfate application episodes (5000 L each) at various Na 2 SO 4 concentrations were allowed to infiltrate under a constant hydraulic head. Although the applied sulfate solution was impacted by density driven advection, detailed monitoring data indicated that the sulfate-enriched water mixed with up-gradient groundwater as it migrated downward through the residual PHC zone and formed a co-mingled downgradient plume with the dissolved PHC compounds. The enrichment of δ 34 S of sulfate in conjunction with a decrease in sulfate concentration showed the occurrence of sulfate reduction due to the applied sulfate. Increased dissolved inorganic carbon (DIC) concentrations associated with a shift toward more depleted values of δ 13 C of DIC was indicative of an input of isotopically depleted DIC from biodegradation of benzene, toluene and o-xylene (BTX). Despite fluctuations in the BTX concentrations, the CSIA data for BTX showed that these compounds were biodegraded. The biomarker data provided supporting evidence that toluene and o-xylene were undergoing anaerobic biodegradation due to sulfate reduction. This study provides insight into factors controlling surface-based delivery of sulfate to shallow PHC impacted groundwater systems, and the value of isotopic and molecular-biological procedures to augment conventional monitoring tools

Microbial community dynamics and stability during an ammonia-induced shift to syntrophic acetate oxidation

Anaerobic digesters rely on the diversity and distribution of parallel metabolic pathways mediated by complex syntrophic microbial communities to maintain robust and optimal performance. Using mesophilic swine waste digesters, we experimented with increased ammonia loading to induce a shift from aceticlastic methanogenesis to an alternative acetate-consuming pathway of syntrophic acetate oxidation. In comparison with control digesters, we observed shifts in bacterial 16S rRNA gene content and in functional gene repertoires over the course of the digesters' 3-year operating period. During the first year, under identical startup conditions, all bioreactors mirrored each other closely in terms of bacterial phylotype content, phylogenetic structure, and evenness. When we perturbed the digesters by increasing the ammonia concentration or temperature, the distribution of bacterial phylotypes became more uneven, followed by a return to more even communities once syntrophic acetate oxidation had allowed the experimental bioreactors to regain stable operation. The emergence of syntrophic acetate oxidation coincided with a partial shift from aceticlastic to hydrogenotrophic methanogens. Our 16S rRNA gene analysis also revealed that acetate-fed enrichment experiments resulted in communities that did not represent the bioreactor community. Analysis of shotgun sequencing of community DNA suggests that syntrophic acetate oxidation was carried out by a heterogeneous community rather than by a specific keystone population with representatives of enriched cultures with this metabolic capacity

Characterization of Trapped Lignin-Degrading Microbes in Tropical Forest Soil

Lignin is often the most difficult portion of plant biomass to degrade, with fungi generally thought to dominate during late stage decomposition. Lignin in feedstock plant material represents a barrier to more efficient plant biomass conversion and can also hinder enzymatic access to cellulose, which is critical for biofuels production. Tropical rain forest soils in Puerto Rico are characterized by frequent anoxic conditions and fluctuating redox, suggesting the presence of lignin-degrading organisms and mechanisms that are different from known fungal decomposers and oxygen-dependent enzyme activities. We explored microbial lignin-degraders by burying bio-traps containing lignin-amended and unamended biosep beads in the soil for 1, 4, 13 and 30 weeks. At each time point, phenol oxidase and peroxidase enzyme activity was found to be elevated in the lignin-amended versus the unamended beads, while cellulolytic enzyme activities were significantly depressed in lignin-amended beads. Quantitative PCR of bacterial communities showed more bacterial colonization in the lignin-amended compared to the unamended beads after one and four weeks, suggesting that the lignin supported increased bacterial abundance. The microbial community was analyzed by small subunit 16S ribosomal RNA genes using microarray (PhyloChip) and by high-throughput amplicon pyrosequencing based on universal primers targeting bacterial, archaeal, and eukaryotic communities. Community trends were significantly affected by time and the presence of lignin on the beads. Lignin-amended beads have higher relative abundances of representatives from the phyla Actinobacteria, Firmicutes, Acidobacteria and Proteobacteria compared to unamended beads. This study suggests that in low and fluctuating redox soils, bacteria could play a role in anaerobic lignin decomposition

Sugarcane mill mud-induced putative host (soybean (Glycine max))-rhizobia symbiosis in sandy loam soil.

Domestic production of controlled-release, compost-based, and microbe-enhanced fertilizers is being expanded in the U.S. as a part of rural development. Sugarcane mill mud is a sterilized (≈90°C) agricultural byproduct in surplus that has received interests as a soil amendment in several Southern states, because of its high phosphorus and organic carbon contents. Addition of mill mud to sandy loam significantly increased the nodule formation compared to fertilized and unfertilized controls. Mill mud addition also resulted in pod yields similar to the fertilized control. Though not found in mill mud itself, mill mud additions correlated with an increase in soil Rhizobia as determined by deep 16S rRNA gene sequencing. We hypothesize that Firmicutes in sterilized mill mud induced Rhizobia that in turn enhanced soybean (Glycine max) growth. Collectively, mill mud enhanced the plant growth promoting bacteria when applied to a silt loam, although the relative influence of mill mud-derived bacteria, organic carbon, and nutrients is yet to be determined

Virome Variation during Sea Star Wasting Disease Progression in Pisaster ochraceus (Asteroidea, Echinodermata)

Sea star wasting disease (SSWD) is a condition that has affected asteroids for over 120 years, yet mechanistic understanding of this wasting etiology remains elusive. We investigated temporal virome variation in two Pisaster ochraceus specimens that wasted in the absence of external stimuli and two specimens that did not experience SSWD for the duration of our study, and compared viromes of wasting lesion margin tissues to both artificial scar margins and grossly normal tissues over time. Global assembly of all SSWD-affected tissue libraries resulted in 24 viral genome fragments represented in >1 library. Genome fragments mostly matched densoviruses and picornaviruses with fewer matching nodaviruses, and a sobemovirus. Picornavirus-like and densovirus-like genome fragments were most similar to viral genomes recovered in metagenomic study of other marine invertebrates. Read recruitment revealed only two picornavirus-like genome fragments that recruited from only SSWD-affected specimens, but neither was unique to wasting lesions. Wasting lesion margin reads recruited to a greater number of viral genotypes (i.e., richness) than did either scar tissue and grossly normal tissue reads. Taken together, these data suggest that no single viral genome fragment was associated with SSWD. Rather, wasting lesion margins may generally support viral proliferation

Integrated Plume Treatment Using Persulfate Coupled with Microbial Sulfate Reduction

The integration or sequential use of different remediation technologies, also referred to as a combined remedy, has become an emerging strategy for the treatment of contaminated sites. Coupling chemical oxidation using persulfate with enhanced bioremediation (EBR) under sulfate reducing conditions is a plausible combined remedy. To characterize the role of the mass removal processes (e.g., chemical oxidation vs. sulfate reduction) and to quantify the impact of persulfate on indigenous microbial processes in a combined persulfate/EBR treatment system, a pilot-scale field experiment was conducted in a 24-m long sheet pile-walled gate over a period of approximately 400d. After dissolved benzene, toluene, and o-xylene (BTX) quasi steady-state plumes were developed, two persulfate injection episodes were performed 10d apart to create a chemical oxidation (ChemOx) zone. High-resolution monitoring was conducted to observe the migration of the ChemOx zone and transition into an EBR zone. Mass loss estimates and geochemical indicators were used to identify the distinct transition between the ChemOx and enhanced biological reactive zones. Compound specific isotope analysis (CSIA) was used to distinguish the dominant mass removal process, and to investigate the occurrence of microbial sulfate reduction. BTX metabolites and reverse-transcriptase quantitative polymerase chain reaction analyses of expressed biodegradation genes (as mRNA) were also used to characterize the response of indigenous microorganisms (especially sulfate-reducing bacteria) to the added persulfate. Multiple lines of evidence supported the conclusion that chemical oxidation was the dominant mass removal process in the vicinity of the injection zone, while enhanced biodegradation dominated BTX degradation in the downgradient portions of the system. The CSIA and supporting molecular biological data were critical in documenting temporally and spatially distinctive zones in this system that were dominated by either chemical-oxidation or anaerobic-biodegradation processes. Initially, persulfate had an inhibitory impact on the activity of the indigenous microbial community, but this was followed by a substantial rebound of microbial activity to above baseline levels. The results from this investigation demonstrate that the suite of diagnostic tools employed can be used to distinguish between chemical oxidation using persulfate and the subsequent effects of the produced sulfate