Recent Publications

Cargo carrying bacteria at interfaces

Vaccari L, Molaei M, Leheny RL, Stebe KJ. Cargo carrying bacteria at interfaces. Soft Matter [Internet]. 2018;(14) :5643-5653. Publisher's VersionAbstract
The displacements of ensembles of colloids at the interface between oil and suspensions of the bacterium Pseudomonas aeruginosa PA14DpelA indicate enhanced colloid mobilities and apparently diffusive motion driven by interactions with the bacteria. However, inspection of individual trajectories of B500 particles reveals prolonged, directed displacements inconsistent with purely hydrodynamic interactions between swimming bacteria and colloids. Analysis of the properties of colloid paths indicates trajectories can be sorted into four distinct categories, including diffusive, persistent, curly, and mixed trajectory types. Non-diffusive trajectories are the norm, comprising 2/3 of the observed trajectories. Imaging of colloids in the interface reveals anisotropic assemblies formed by colloids decorated with one or more adhered bacteria that drive the colloids along these paths. The trajectories and enhanced transport result from individual colloids being moved as cargo by these adhered bacteria. The implications of these structures and open questions for interfacial transport are discussed and related to the active colloid literature. 
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Environmental petroleum pollution analysis using ramped pyrolysis-gas chromatography-mass spectrometry

Seeley Evans M, Wang Q, Bacosa H, Rosenheim BE, Liu Z. Environmental petroleum pollution analysis using ramped pyrolysis-gas chromatography-mass spectrometry. Organic Geochemistry [Internet]. 2018;124 :180-189. Publisher's VersionAbstract
In response to the Deepwater Horizon oil spill, critical research has tracked the changes in petroleum hydrocarbons with environmental weathering. There are limitations, however, whereby single analytical techniques cannot always identify the wide breadth of petroleum and petroleum-derived compounds. We explore the analytical capabilities of ramped pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS) to evaluate environmental samples of petroleum hydrocarbons from the Deepwater Horizon oil spill. We show that bulk flow Py-GC–MS can quantify the overall degree of petroleum hydrocarbon weathering. Furthermore, thermal slicing Py-GC–MS can quantify specific compounds in the “thermal desorption zone” (50–370 °C), as well as characterize pyrolyzed fragments from non-GC-amenable petroleum hydrocarbons (including oxygenated hydrocarbons) in the “cracking zone” (370–650 °C). Our data also suggest an increase in thermochemical stability, concentration of oxygenated products and complexity of high molecular weight and/or polar components with advanced weathering. This analysis not only elucidates weathering trends in Deepwater Horizon oil over several years, but also illustrates the analytical capacity of this method for future petroleum hydrocarbon investigations, filling a void in research connecting Py-GC–MS and environmentally weathered oil samples.
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Oil Spills and Dispersants Can Cause the Initiation of Potentially Harmful Dinoflagellate Blooms (“Red Tides”)

Almeda R, Cosgrove S, Buskey EJ. Oil Spills and Dispersants Can Cause the Initiation of Potentially Harmful Dinoflagellate Blooms (“Red Tides”). Environmental Science & Technology [Internet]. 2018. Publisher's VersionAbstract
ABSTRACT: After oil spills and dispersant applications the formation
of red tides or harmful algal blooms (HABs) has been observed, which
can cause additional negative impacts in areas affected by oil spills.
However, the link between oil spills and HABs is still unknown. Here,
we present experimental evidence that demonstrates a connection
between oil spills and HABs. We determined the effects of oil,
dispersant-treated oil, and dispersant alone on the structure of natural
plankton assemblages in the Northern Gulf of Mexico. In coastal
waters, large tintinnids and oligotrich ciliates, major grazers of phytoplankton, were negatively affected by the exposure to oil and dispersant, whereas bloom-forming dinoflagellates (Prorocentrum texanum, P. triestinum, and Scrippsiella trochoidea) notably increased their concentration. The removal of key grazers due to oil and dispersant disrupts the predator−prey controls (“top-down controls”) that normally function in plankton food webs. This disruption of grazing pressure opens a “loophole” that allows certain dinoflagellates with higher tolerance to oil and dispersants than their grazers to grow and form blooms when there are no growth limiting factors (e.g., nutrients). Therefore, oil spills and dispersants can act as disrupters of predator−prey controls in plankton food webs and as indirect inducers of potentially harmful dinoflagellate blooms.
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Impact of particle concentration and out-of-range sizes on the measurements of the LISST

Zhao L, Boufadel M, King T, Robinson B, Conmy R, Lee K. Impact of particle concentration and out-of-range sizes on the measurements of the LISST. Measurement Science and Technology [Internet]. 2018;29 (5). Publisher's VersionAbstract
The instrument LISST (laser in situ scattering and transmissiometry) has been widely used for measuring the size of oil droplets in relation to oil spills and sediment particles. Major concerns associated with using the instrument include the impact of high concentrations and/or out-of-range particle (droplet) sizes on the LISST reading. These were evaluated experimentally in this study using monosized microsphere particles. The key findings include: (1) When high particle concentration reduced the optical transmission (OT) to below 30%, the measured peak value tended to underestimate the true peak value, and the accuracy of the LISST decreased by ~8% to ~28%. The maximum concentration to reach the 30% OT was about 50% of the theoretical values, suggesting a lower concentration level should be considered during the instrument deployment. (2) The out-of-range sizes of particles affected the LISST measurements when the sizes were close to the LISST measurement range. Fine below-range sizes primarily affected the data in the lowest two bins of the LISST with  >75% of the volume at the smallest bin. Large out-of-range particles affected the sizes of the largest 8–10 bins only when very high concentration was present. The out-of-range particles slightly changed the size distribution of the in-range particles, but their concentration was conserved. An approach to interpret and quantify the effects of the out-of-range particles on the LISST measurement was proposed.
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Rapid alterations to marine microbiota communities following an oil spill

Gemmell BJ, Bacosa HP, Dickey BO, Gemmell CG, Alqasemi LR, Buskey EJ. Rapid alterations to marine microbiota communities following an oil spill. Ecotoxicology [Internet]. 2018 :1-12. Publisher's VersionAbstract
Field data from the first several days after an oil spill is rare but crucial for our understanding of a spill’s impact on marine microbiota given their short generation times. Field data collected within days of the Texas City “Y” oil spill showed that exposure to crude oil can rapidly imbalance populations of marine microbiota, which leads to the proliferation of more resistant organisms. Vibrionales bacteria were up to 48 times higher than background concentrations at the most impacted sites and populations of the dinoflagellate Prorocentrum texanum increased significantly as well. Laboratory microcosm experiments with a natural plankton community showed that P. texanum grew significantly faster under oiled conditions but monocultures of P. texanum did not. Additional laboratory experiments with natural communities from Tampa Bay, Florida showed similar results although a different species dominated, P. minimum. In both cases, tolerance to the presence of crude oil was enhanced by higher sensitivity of grazers led to a release from grazing pressure and allows Prorocentrum species to dominate after an oil spill. The results suggest careful monitoring for Vibrionales and Prorocentrum during future spills would be beneficial given the potential implications to human health.
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