Electrical Resistivity Imaging for Long-Term Autonomous Monitoring of Hydrocarbon Degradation: Lessons from the Deepwater Horizon Oil Spill

Conceptual models for the geophysical responses associated with hydrocarbon degradation suggest that the long-term evolution of an oil plume will result in a more conductive anomaly than the initial contamination. In response to the Deepwater Horizon (DH) oil spill into the Gulf of Mexico in 2010, an autonomous resistivity monitoring system was deployed on Grand Terre, Louisiana, in an attempt to monitor natural degradation processes in hydrocarbon-impacted beach sediments of this island. A 48-electrode surface array with a 0.5-m spacing was installed to obtain twice-daily images of the resistivity structure of the shallow subsurface impacted by oil. Over the course of approximately 18 months, we observed a progressive decrease in the resistivity of the DH spill-impacted region. Detailed analysis of pixel/point resistivity variation within the imaged area showed that long-term decreases in resistivity were largely associated with the DH-impacted sediments. A microbial diversity survey revealed the presence of hydrocarbon-degrading organisms throughout the test site. However, hydrocarbon degradation activity was much higher in the DH-impacted locations compared to nonimpacted locations, suggesting the presence of active hydrocarbon degraders, supporting biodegradation processes. The results of this long-term monitoring experiment suggested that resistivity might be used to noninvasively monitor the long-term degradation of crude oil spills

Arhodomonas sp. strain Seminole and its genetic potential to degrade aromatic compounds under high-salinity conditions

Arhodomonas sp. strain Seminole was isolated from a crude oil-impacted brine soil and shown to degrade benzene, toluene, phenol, 4-hydroxybenzoic acid (4-HBA), protocatechuic acid (PCA), and phenylacetic acid (PAA) as the sole sources of carbon at high salinity. Seminole is a member of the genus Arhodomonas in the class Gammaproteobacteria, sharing 96% 16S rRNA gene sequence similarity with Arhodomonas aquaeolei HA-1. Analysis of the genome predicted a number of catabolic genes for the metabolism of benzene, toluene, 4-HBA, and PAA. The predicted pathways were corroborated by identification of enzymes present in the cytosolic proteomes of cells grown on aromatic compounds using liquid chromatography-mass spectrometry. Genome analysis predicted a cluster of 19 genes necessary for the breakdown of benzene or toluene to acetyl coenzyme A (acetyl-CoA) and pyruvate. Of these, 12 enzymes were identified in the proteome of toluene-grown cells compared to lactate-grown cells. Genomic analysis predicted 11 genes required for 4-HBA degradation to form the tricarboxylic acid (TCA) cycle intermediates. Of these, proteomic analysis of 4-HBA-grown cells identified 6 key enzymes involved in the 4-HBA degradation pathway. Similarly, 15 genes needed for the degradation of PAA to the TCA cycle intermediates were predicted. Of these, 9 enzymes of the PAA degradation pathway were identified only in PAA-grown cells and not in lactate-grown cells. Overall, we were able to reconstruct catabolic steps for the breakdown of a variety of aromatic compounds in an extreme halophile, strain Seminole. Such knowledge is important for understanding the role of Arhodomonas spp. in the natural attenuation of hydrocarbon-impacted hypersaline environments.Peer reviewedMicrobiology and Molecular GeneticsBiochemistry and Molecular Biolog

Proteogenomic elucidation of the initial steps in the benzene degradation pathway of a novel halophile, Arhodomonas sp. strain Rozel, isolated from a hypersaline environment

Lately, there has been a special interest in understanding the role of halophilic and halotolerant organisms for their ability to degrade hydrocarbons. The focus of this study was to investigate the genes and enzymes involved in the initial steps of the benzene degradation pathway in halophiles. The extremely halophilic bacteria Arhodomonas sp. strain Seminole and Arhodomonas sp. strain Rozel, which degrade benzene and toluene as the sole carbon source at high salinity (0.5 to 4 M NaCl), were isolated from enrichments developed from contaminated hypersaline environments. To obtain insights into the physiology of this novel group of organisms, a draft genome sequence of the Seminole strain was obtained. A cluster of 13 genes predicted to be functional in the hydrocarbon degradation pathway was identified from the sequence. Two-dimensional (2D) gel electrophoresis and liquid chromatography-mass spectrometry were used to corroborate the role of the predicted open reading frames (ORFs). ORFs 1080 and 1082 were identified as components of a multicomponent phenol hydroxylase complex, and ORF 1086 was identified as catechol 2,3-dioxygenase (2,3-CAT). Based on this analysis, it was hypothesized that benzene is converted to phenol and then to catechol by phenol hydroxylase components. The resulting catechol undergoes ring cleavage via the meta pathway by 2,3-CAT to form 2-hydroxymuconic semialdehyde, which enters the tricarboxylic acid cycle. To substantiate these findings, the Rozel strain was grown on deuterated benzene, and gas chromatography-mass spectrometry detected deuterated phenol as the initial intermediate of benzene degradation. These studies establish the initial steps of the benzene degradation pathway in halophiles.Peer reviewedMicrobiology and Molecular Genetic

Factors Affecting the Methanogenic Activity of Methanothrix soehngenii VNBF

Methane production by Methanothrix soehngenii VNBF grown on acetate (50 mM) as the sole carbon and energy source was influenced by the addition of Fe, trace elements, and pesticides. The addition of Fe and trace elements significantly enhanced the rate of CH(4) production. The addition of pesticides in the early growth phase caused complete inhibition. However, less inhibition was noted when pesticides were added during early exponential growth phase. Addition to culture tubes of Co, Ni, or Mo at 2 μM produced 64, 41, or 17%, respectively, more CH(4) than that produced in tubes lacking the corresponding trace element. A concentration of more than 5 μM of these trace elements in the medium resulted in decreased CH(4) production, presumably because of toxic effects

Isolation and characterization of an aceticlastic methanogen from a biogas digester

Isolation and characterization of a fast-growing filament-forming methanogen (Methanothrix soehngenii strain VNBF) which uses acetate as the sole energy source for growth are reported. The stoichiometric conversion of acetate to CH4 [74-82-8] in the absence of added H suggests that all the CH4 is derived most probably from the Me group of acetate. The strain VNBF may be playing a key role in methanogenesis from org. wastes. Its high efficiency of CH4 prodn. may help to improve the performance of biogas digesters

Biodegradation of Benzene by Halophilic and Halotolerant Bacteria under Aerobic Conditions

A highly enriched halophilic culture was established with benzene as the sole carbon source by using a brine soil obtained from an oil production facility in Oklahoma. The enrichment completely degraded benzene, toluene, ethylbenzene, and xylenes within 1 to 2 weeks. Also, [(14)C]benzene was converted to (14)CO(2), suggesting the culture's ability to mineralize benzene. Community structure analysis revealed that Marinobacter spp. were the dominant members of the enrichment