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Petroleum products in the environment can produce significant toxicity through photochemically driven processes. Burning surface oil and photochemical degradation were two mechanisms for oil removal after the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico. After burning, residual oil remains in the environment and may undergo further weathering, a poorly understood fate. Although photochemistry was a major degradation pathway of the DWH oil, its effect on burned oil residue in the environment is under studied. Here, we ignited Macondo surrogate crude oil and allowed it to burn to exhaustion. Water-accommodated fractions (WAFs) of the burn residue were created in full sunlight to determine the effects of photochemical weathering on the burned oil residue. Our findings show that increased dissolved organic carbon concentrations (DOC) for the light unburned and light burned after sunlight exposure positively correlated to decreased microbial growth and production inhibition (i.e. more toxic) when compared to the dark controls. Optical and molecular analytical techniques were used to identify the classes of compounds contributing to the toxicity in the dark and light burned and dark and light unburned WAFs. After light exposure, the optical composition between the light unburned and light burned differed significantly (p < 0.05), revealing key fluorescence signatures commonly identified as crude oil degradation products. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis showed more condensed aromatic, reduced oxygenated compounds present in the light burned than in the light unburned. FT-ICR MS also showed an increase in the percent relative abundance of carboxyl-rich alicyclic molecules (CRAM) like compounds in the light burned compared to light unburned. The increase in CRAM suggests that the composition of the light burned is more photorefractory, i.e., reduced, explaining the residual toxicity observed in microbial activity. Overall, these data indicate burning removes some but not all toxic compounds, leaving behind compounds which retain considerable toxicity. This study shows that burn oil residues are photolabile breaking down further into complex reduced compounds. [ABSTRACT FROM AUTHOR]

The 2010 Deepwater Horizon (DwH) Oil spill released an enormous volume of oil into the Gulf of Mexico (GoM), prompting the widespread use of chemical dispersants like Corexit® EC9500A. The ecological consequences of this treatment, especially when combined with natural factors such as sunlight, remain unexplored in the context of marine bacterial communities' dynamics. To address this knowledge gap, our study employed a unique metaproteomic approach, investigating the combined effects of sunlight, crude Macondo surrogate oil, and Corexit on GoM microbiome across different mesocosms. Exposure to oil and/or Corexit caused a marked change in community composition, with a decrease in taxonomic diversity relative to controls in only 24 hours. Hydrocarbon (HC) degraders, particularly those more tolerant to Corexit and phototoxic properties of crude oil and/or Corexit, proliferated at the expense of more sensitive taxa. Solar radiation exacerbated these effects in most taxa. We demonstrated that sunlight increased the dispersant's toxicity, impacting on community structure and functioning. These functional changes were primarily directed by oxidative stress with upregulated proteins and enzymes involved in protein turnover, general stress response, DNA replication and repair, chromosome condensation, and cell division. These factors were more abundant in chemically treated conditions, especially in the presence of Corexit compared to controls. Oil treatment significantly enhanced the relative abundance of Alteromonas, an oil-degrading Gammaproteobacteria. In combined oil-Corexit treatments, the majority of identified protein functions were assigned to Alteromonas, with strongly expressed proteins involved in membrane transport, motility, carbon and amino acid metabolism and cellular defense mechanisms. Marinomonas, one of the most active genera in dark conditions, was absent from the light treatment. Numerous metabolic pathways and HC-degrading genes provided insights into bacterial community adaptation to oil spills. Key enzymes of the glyoxylate bypass, enriched in contaminant-containing treatments, were predominantly associated with Rhodobacterales and Alteromonadales. Several proteins related to outer membrane transport, photosynthesis, and nutrient metabolisms were characterized, allowing predictions of the various treatments on biogeochemical cycles. The study also presents novel perspectives for future oil spill clean-up processes. [ABSTRACT FROM AUTHOR]

Research was conducted to examine the molecular and biological consequences of UV-B radiation by investigating five species of marine bacteria and one enteric bacterium. The relative contributions of dark- and light-dependent repair systems to recovery were calculated by measuring survival and induction and repair of cyclobutane pyrimidine dimers under various light conditions. Results illustrate that there are wide variations in marine bacteria in their responses to UV radiation and subsequent repair strategies indicating that UV-B radiation may influence the microbial community structure in surface water.

Analysis of samples collected at a mercury-contaminated fresh-water pond helps examine the relationship between merA gene expression and mercury volatilization in aquatic microbial communities. Mercury concentration in water and microbial heterotrophic activity exert a strong influence on the levels of merA mRNA transcripts and the rate of inorganic Hg volatilization. The influence of microbial metabolic activity on levels of merA-specific mRNA and Hg(II) volatilization is higher than that of Hg concentration. Mercury volatilization need not be proportional to merA expression.

Boiling sodium dodecyl sulfate-diethylpyrocarbonate lysis combined with acid-guanidinium extraction recovers undamaged, contaminating DNA free, mRNA target sequences from environment and pure cultures. The mRNA detects mercuric reductase A transcripts in the microbial population of mercury-contaminated pond water and enhances the study of mer gene characteristics.

The Pseudomonas putida TOL plasmid codes for various enzymes required for the conversion of benzoate to catechol. P. putida mutants unable to convert benzoate to catechol were generated and characterized, resulting in the isolation of mutants deficient in specific enzymes or functions. Complementation tests showed that a P. putida chromosomal gene could complement a defect in xylS, which positively regulates benzoate oxidation. However, DNA hybridization experiments showed that the sequence of benR is not similar to xylS.

A population of the rarely reported diatomNanoneis longtawas observed over a period of more than two years in the northeastern Gulf of Mexico. This permitted a detailed examination of the fine structure of the valve in scanning and transmission electron microscopy. The population matched the basic features of the original description of the species, but displayed a greater size range. Our use of SEM revealed the presence of a novel structure, the porticus marginalis, along the perimeter of the valve. The species was most abundant below the thermocline, at depths between 25 and 125 m, and from summer to early fall. An emended definition of the species to accommodate the observed size range and the new feature is included. [ABSTRACT FROM PUBLISHER]