Microbial Activities and Dissolved Organic Matter Dynamics in Oil-Contaminated Surface Seawater from the Deepwater Horizon Oil Spill Site

The Deepwater Horizon oil spill triggered a complex cascade of microbial responses that reshaped the dynamics of heterotrophic carbon degradation and the turnover of dissolved organic carbon (DOC) in oil contaminated waters. Our results from 21-day laboratory incubations in rotating glass bottles (roller bottles) demonstrate that microbial dynamics and carbon flux in oil-contaminated surface water sampled near the spill site two weeks after the onset of the blowout were greatly affected by activities of microbes associated with macroscopic oil aggregates. Roller bottles with oil-amended water showed rapid formation of oil aggregates that were similar in size and appearance compared to oil aggregates observed in surface waters near the spill site. Oil aggregates that formed in roller bottles were densely colonized by heterotrophic bacteria, exhibiting high rates of enzymatic activity (lipase hydrolysis) indicative of oil degradation. Ambient waters surrounding aggregates also showed enhanced microbial activities not directly associated with primary oil-degradation (β-glucosidase; peptidase), as well as a twofold increase in DOC. Concurrent changes in fluorescence properties of colored dissolved organic matter (CDOM) suggest an increase in oil-derived, aromatic hydrocarbons in the DOC pool. Thus our data indicate that oil aggregates mediate, by two distinct mechanisms, the transfer of hydrocarbons to the deep sea: a microbially-derived flux of oil-derived DOC from sinking oil aggregates into the ambient water column, and rapid sedimentation of the oil aggregates themselves, serving as vehicles for oily particulate matter as well as oil aggregate-associated microbial communities

PAH mineralization and bacterial organotolerance in surface sediments of the Charleston Harbor estuary

Semi-volatile organic compounds (SVOCs) in estuarine waters can adversely affect biota but watershed sources can be difficult to identify because these compounds are transient. Natural bacterial assemblages may respond to chronic, episodic exposure to SVOCs through selection of more organotolerant bacterial communities. We measured bacterial production, organotolerance and polycyclic aromatic hydrocarbon (PAH) mineralization in Charleston Harbor and compared surface sediment from stations near a known, permitted SVOC outfall (pulp mill effluent) to that from more pristine stations. Naphthalene additions inhibited an average of 77% of bacterial metabolism in sediments from the more pristine site (Wando River). Production in sediments nearest the outfall was only inhibited an average of 9% and in some cases, was actually stimulated. In general, the stations with the highest rates of bacterial production also were among those with the highest rates of PAH mineralization. This suggests that the capacity to mineralize PAH carbon is a common feature amongst the bacterial assemblage in these estuarine sediments and could account for an average of 5.6% of bacterial carbon demand (in terms of production) in the summer, 3.3% in the spring (April) and only 1.2% in winter (December)

Internal consistency of the self-reporting questionnaire-20 in occupational groups

ABSTRACT OBJECTIVE To assess the internal consistency of the measurements of the Self-Reporting Questionnaire (SRQ-20) in different occupational groups. METHODS A validation study was conducted with data from four surveys with groups of workers, using similar methods. A total of 9,959 workers were studied. In all surveys, the common mental disorders were assessed via SRQ-20. The internal consistency considered the items belonging to dimensions extracted by tetrachoric factor analysis for each study. Item homogeneity assessment compared estimates of Cronbach’s alpha (KD-20), the alpha applied to a tetrachoric correlation matrix and stratified Cronbach’s alpha. RESULTS The SRQ-20 dimensions showed adequate values, considering the reference parameters. The internal consistency of the instrument items, assessed by stratified Cronbach’s alpha, was high (> 0.80) in the four studies. CONCLUSIONS The SRQ-20 showed good internal consistency in the professional categories evaluated. However, there is still a need for studies using alternative methods and additional information able to refine the accuracy of latent variable measurement instruments, as in the case of common mental disorders

Fluxes of water, sediments, and biogeochemical compounds in salt marshes

Tidal oscillations systematically flood salt marshes, transporting water, sediments, organic matter, and biogeochemical elements such as silica. Here we present a review of recent studies on these fluxes and their effects on both ecosystem functioning and morphological evolution of salt marshes. We reexamine a simplified model for the computation of water fluxes in salt marshes that captures the asymmetry in discharge between flood and ebb. We discuss the role of storm conditions on sediment fluxes both in tidal channels and on the marsh platform. We present recent methods and field instruments for the measurement of fluxes of organic matter. These methods will provide long-term data sets with fine temporal resolution that will help scientists to close the carbon budget in salt marshes. Finally, the main processes controlling fluxes of biogenic and dissolved silica in salt marshes are explained, with particular emphasis on the uptake by marsh macrophytes and diatoms

TRANSIENT RESPONSES OF MYOSTATIN SIGNALING MARKERS TO ACUTE BOUTS OF RESISTANCE TRAINING

Mason C. McIntosh, Casey L. Sexton, Joshua L. Godwin, Bradley A. Ruple, Shelby C. Osburn, John M. Michel, Daniel L. Plotkin, Christopher B. Mobley, Michael D. Roberts. Auburn University, Auburn, AL. BACKGROUND: The myostatin (MSTN) gene has been heavily researched for its role in repressing skeletal muscle hypertrophy and the anabolic mTORC1 signaling pathway. Preliminary data from our laboratory has shown a significant hypermethylation of cytosine phosphate guanine sites within the MSTN gene as well as a significant downregulation of MSTN mRNA following acute bouts of resistance exercise to failure (i.e., training at 30% one repetition maximum versus 80% one repetition maximum). This study sought to determine the changes of MSTN-related and mTORC1 signaling proteins following two bouts of resistance exercise to failure. We hypothesized there to be significant time-effects of assayed markers in response to each bout of resistance training. METHODS: Eleven previously-trained college-aged men (age: 23 ± 4 years, 11.4 ± 6.4 percent fat, 4 ± 3 years training experience) participated in this study. Each participant performed two resistance training sessions (spaced one week apart) involving either: i) 30FAIL training; 4 sets of back squats and 4 sets of leg extensors to failure at 30% of one-repetition maximum (1RM), or: ii) 80FAIL training; 4 sets of both exercises at 80% of 1RM. Vastus lateralis muscle biopsies were obtained prior to each training session (PRE), 3 hours following training (3hPOST), and 6 hours following training (6hPOST). Western blots were performed on biopsied muscle to determine the relative expression of phosphorylated (p)-mTOR (Ser2448), p-p70S6K (Thr389), p-AKT (Ser473), p-rpS6 (Ser235/236), follistatin (FST), and MSTN. RESULTS: There were no significant bout*time interactions for any of the assayed markers. There were significant differences observed for p-p70S6K (p=0.001; PRE to 3hPOST) and FST (p=0.021; PRE to 6hPOST). There were no significant main time effects observed for p-mTOR, p-AKT, or p-rps6. CONCLUSIONS: The two modes of resistance training elicited similar effects on p-p70S6K and FST protein expression. These results suggest, regardless of training load, mTORC1 markers and MTSN-related protein expression respond similarly in previously-trained college-aged men