Responses of microbial community from northern Gulf of Mexico sandy sediments following exposure to deepwater horizon crude oil

Abstract

In the present study, microbial community responses to exposure to unweathered Macondo Well crude oil and conventional diesel in a sandy beach environment were determined. Biodegradation was assessed in mesocosm experiments with differing fuel amounts (2,000 and 4,000 mg/kg) and with or without inorganic nutrient amendment. Carbon dioxide production was measured daily for 42 d. Aerobic alkane, total hydrocarbon, and polycyclic aromatic hydrocarbon (PAH) degraders were enumerated in treated and control mesocosms and changes in their abundances were measured weekly. Hydrocarbon mineralization occurred in all treatments. In the inorganic nutrient-amended treatments, the degradation rates were 2.31 and 2.00 times greater in the 2,000 mg/kg diesel and crude oil treatments, respectively, and 3.52 (diesel) and 4.14 (crude) times higher for the fuel types at the 4,000 mg/kg fuel concentrations compared to unamended treatments. Microbial lag phases were short (<3 d) and alkane and total hydrocarbon degrader numbers increased by five orders of magnitude compared to the uncontaminated treatments within 7 d in most treatments. Hydrocarbon degrader numbers in diesel and in crude oil treatments were similar; however, the PAH degraders were more abundant in the crude oil relative to diesel treatment. These findings indicate that hydrocarbon degradation by extant microbial populations in the northern Gulf of Mexico sandy beach environments can be stimulated and enhanced by inorganic nutrient addition.

Salt Marsh Bacterial Communities before and after the Deepwater Horizon Oil Spill

“…Comparing our findings with results from those earlier studies indicates that the DWH oil spill appeared to cause a rapid response among bacterial communities from salt marshes (37,40,42), the open ocean (90,96,97,(108)(109)(110), and sandy beaches (94,95,(111)(112)(113)(114). Initially, we observed that marsh bacterial communities were dominated by Proteobacteria, which were replaced by Firmicutes only 4 months later.…”

Input of organic matter enhances degradation of weathered diesel fuel in sub-tropical sediments

“…A significant decline in pH during hydrocarbon degradation could be expected (Wrenn et al, 1994); however in the present study the measured pH values resulted in minimal concern for acidity and were in general within the range for feasible hydrocarbon degradation (Das and Chandran, 2011). Total dissolved inorganic nitrogen (TDIN) and phosphorous (as PO 4 3− ) in sediments at the site had a concentration of 0.113 mg N kg −1 , and 0.412 mg P kg −1 sediment, respectively, suggesting low nutrient availability, especially when compared to previous investigations at nearby study areas (Horel et al, 2012a;Mortazavi et al, 2013b).…”

“…1b) which was considerably lower than observed for the C. chrysurus treatments (103.6%). In a previous study where fresh diesel fuel contaminated sediments were amended with inorganic nutrients, daily respiration rates were similar, but cumulative mineralization at 42 days was somewhat higher (total CO 2 based mineralization of 39.9% versus 27.0%) (Horel et al, 2012a).…”

“…Headspace air was analyzed for CO 2 concentrations daily, as described by Horel et al (2012a), with a Shimadzu Gas Chromatograph (8A) equipped with a Thermal Conductivity Detector (GC-TCD).…”

“…In addition to the amount of contamination at a site, the nature of the hydrocarbon(s) physical and chemical characteristics will also affect biodegradation rates (Alexander, 1999;Horel et al, 2012a). Upon weathering of many diesel fuel types, volatile compounds decrease (i.e., 8-10% remaining) (Energy Laboratories Inc., 2005;Horel and Schiewer, 2009) and the intermediate chain length alkanes can be degraded by hydrocarbon degrading microorganisms at a rate faster than that of the longer chain alkanes which are recalcitrant to biodegradation (Atlas and Bartha, 1998;Mortazavi et al, 2013a).…”