Dynamics and distribution of bacterial and archaeal communities in oil-contaminated temperate coastal mudflat mesocosms

Mudflats are ecologically important habitats that are susceptible to oil pollution, but intervention is difficult in these fine-grained sediments, and so clean-up usually relies on natural attenuation. Therefore, we investigated the impact of crude oil on the bacterial, diatom and archaeal communities within the upper parts of the diatom-dominated sediment and the biofilm that detached from the surface at high tide. Biodegradation of petroleum hydrocarbons was rapid, with a 50 % decrease in concentration in the 0–2-mm section of sediment by 3 days, indicating the presence of a primed hydrocarbon-degrading community. The biggest oil-induced change was in the biofilm that detached from the sediment, with increased relative abundance of several types of diatom and of the obligately hydrocarbonoclastic Oleibacter sp., which constituted 5 % of the pyrosequences in the oiled floating biofilm on day 3 compared to 0.6 % in the non-oiled biofilm. Differences in bacterial community composition between oiled and non-oiled samples from the 0–2-mm section of sediment were only significant at days 12 to 28, and the 2–4-mm-sediment bacterial communities were not significantly affected by oil. However, specific members of the Chromatiales were detected (1 % of sequences in the 2–4-mm section) only in the oiled sediment, supporting other work that implicates them in anaerobic hydrocarbon degradation. Unlike the Bacteria, the archaeal communities were not significantly affected by oil. In fact, changes in community composition over time, perhaps caused by decreased nutrient concentration and changes in grazing pressure, overshadowed the effect of oil for both Bacteria and Archaea. Many obligate hydrocarbonoclastic and generalist oil-degrading bacteria were isolated, and there was little correspondence between the isolates and the main taxa detected by pyrosequencing of sediment-extracted DNA, except for Alcanivorax, Thalassolituus, Cycloclasticus and Roseobacter spp., which were detected by both methods

Influence of aerobic fitness on gastrointestinal barrier integrity and microbial translocation following a fixed-intensity military exertional heat stress test

Purpose: Exertional-heat stress adversely disrupts gastrointestinal (GI) barrier integrity, whereby subsequent microbial translocation (MT) can result in potentially serious health consequences. To date, the influence of aerobic fitness on GI barrier integrity and MT following exertional-heat stress is poorly characterised. Method: Ten untrained (UT; VO2max = 45 ± 3 ml·kg−1·min−1) and ten highly trained (HT; VO2max = 64 ± 4 ml·kg−1·min−1) males completed an ecologically valid (military) 80-min fixed-intensity exertional-heat stress test (EHST). Venous blood was drawn immediately pre- and post-EHST. GI barrier integrity was assessed using the serum dual-sugar absorption test (DSAT) and plasma Intestinal Fatty-Acid Binding Protein (I-FABP). MT was assessed using plasma Bacteroides/total 16S DNA. Results: UT experienced greater thermoregulatory, cardiovascular and perceptual strain (p < 0.05) than HT during the EHST. Serum DSAT responses were similar between the two groups (p = 0.59), although Δ I-FABP was greater (p = 0.04) in the UT (1.14 ± 1.36 ng·ml−1) versus HT (0.20 ± 0.29 ng·ml−1) group. Bacteroides/Total 16S DNA ratio was unchanged (Δ; -0.04 ± 0.18) following the EHST in the HT group, but increased (Δ; 0.19 ± 0.25) in the UT group (p = 0.05). Weekly aerobic training hours had a weak, negative correlation with Δ I-FABP and Bacteroides/total 16S DNA responses. Conclusion: When exercising at the same absolute workload, UT individuals are more susceptible to small intestinal epithelial injury and MT than HT individuals. These responses appear partially attributable to greater thermoregulatory, cardiovascular, and perceptual strain

Ring-hydroxylating dioxygenase (RHD) expression in a microbial community during the early response to oil pollution

cited By 12International audienceThe early functional response of a bacterial community from the sediments of a chronically oil-polluted retention basin located at the Etang de Berre (France) was investigated just after petroleum addition. After removing hydrocarbon compounds by natural abiotic and biotic processes, the sediments were maintained in microcosms and Vic Bilh petroleum was added. The diversity and the expression of genes encoding ring-hydroxylating dioxygenases (RHD) were examined just after the petroleum addition until 14 days focussing on the first hours following the contamination. RHD gene copy numbers and diversity were maintained throughout all the incubation period; however, transcripts were detected only during the first 2 days. One dominant RHD gene, immediately and specifically expressed in response to petroleum contamination, was related to RHD gene carried by a plasmid found in Pseudomonas spp. The expression of the RHD genes was correlated with high biodegradation levels observed for low molecular weight PAHs at 7 days of incubation. The study shows that the bacterial metabolism induced just after the oil input is a key stage that could determine the bacterial community structure changes. Monitoring the expression of RHD genes, key genes involved in hydrocarbon degradation, may provide useful information for managing bioremediation processes. © 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved

Abundance, Diversity and Activity of Sulfate-Reducing Prokaryotes in Heavy Metal-Contaminated Sediment from a Salt Marsh in the Medway Estuary (UK)

International audienceWe investigated the diversity and activity of sulfate-reducing prokaryotes (SRP) in a 3.5-m sediment core taken from a heavy metal-contaminated site in the Medway Estuary, UK. The abundance of SRPs was quantified by qPCR of the dissimilatory sulfite reductase gene β-subunit (dsrB) and taking into account DNA extraction efficiency. This showed that SRPs were abundant throughout the core with maximum values in the top 50 cm of the sediment core making up 22.4% of the total bacterial community and were 13.6% at 250 cm deep. Gene libraries for dsrA (dissimilatory sulfite reductase α-subunit) were constructed from the heavily contaminated (heavy metals) surface sediment (top 20 cm) and from the less contaminated and sulfate-depleted, deeper zone (250 cm). Certain cloned sequences were similar to dsrA found in members of the Syntrophobacteraceae, Desulfobacteraceae and Desulfovibrionaceae as well as a large fraction (60%) of novel sequences that formed a deep branching dsrA lineage. Phylogenetic analysis of metabolically active SRPs was performed by reverse transcription PCR and single strand conformational polymorphism analysis (RT-PCR-SSCP) of dsrA genes derived from extracted sediment RNA. Subsequent comparative sequence analysis of excised SSCP bands revealed a high transcriptional activity of dsrA belonging to Desulfovibrio species in the surface sediment. These results may suggest that members of the Desulfovibrionaceae are more active than other SRP groups in heavy metal-contaminated surface sediments

Evaluation and optimization of nucleic acid extraction methods for the molecular analysis of bacterial communities associated with corroded carbon steel

International audienceDifferent DNA and RNA extraction approaches were evaluated and protocols optimized on in situ corrosion products from carbon steel in marine environments. Protocols adapted from the PowerSoil DNA/RNA Isolation methods resulted in the best nucleic acid (NA) extraction performances (ie combining high NA yield, quality, purity, representativeness of microbial community and processing time efficiency). The PowerSoil RNA Isolation Kit was the only method which resulted in amplifiable RNA of good quality (ie intact 16S/23S rRNA). Sample homogenization and hot chemical (SDS) cell lysis combined with mechanical (bead-beating) lysis in presence of a DNA competitor (skim milk) contributed to improving substantially (around 23 times) the DNA yield of the PowerSoil DNA Isolation Kit. Apart from presenting NA extraction strategies for optimizing extraction parameters with corrosion samples from carbon steel, this study proposes DNA and RNA extraction procedures suited for comparative molecular analysis of total and active fractions of bacterial communities associated with carbon steel corrosion events, thereby contributing to improved MIC diagnosis and control

Heat stability and degradation of thermostable prepolymers in a controlled atmosphere - I: The heat cycle of propargylic monomer homopolymerization, and characterization of adducts.

International audienceThe liquid study of propargylic monomers during heat treatment has shown the formation of secondary phenolic products in the reaction mixture. They are in the form of propargyl-phenol and chromene-phenol and could be the weak links in the thermal properties of the final polymer. Moreover, we note some differences between the reactivities of the two monomers, probably related to the nature of the central pivot of the skeleton. Solid state analyses by FTIR and sold state crossed polarization magic angle spinning C-13 NMR have confirmed the structure of the final polymer, and the reaction paths proposed and have enabled the heat cycle used to be validated. Thermal analyses have shown that the fluorine pivot confers the best thermal properties on the crosslinked material and influences the reactivity and degradation mechanisms of the compounds. In addition, the degradation of the crosslinked compounds occurred as a single step for the dipropargyl ether of bisphenol A and as two steps for the dipropargyl ether of hexafluorobisphenol A

Heat stability and degradation of thermally stable prepolymers in a controlled atmosphere - II: Heat stability and degradation of acetylene-chromene terminated prepolymers

International audienceThe heat stability and thermal degradation of two acetylene-chromene terminated polymers, called polyA (polymer of 6,6'-isopropyl dichroman) and polyF (polymer of 6,6'-hexafluoroisopropyl dichroman) were investigated in controlled conditions. The environmental impact of their degradation was studied in order to predict their remediation and fate after use. Degradation of the polymers was followed by dynamic thermogravimetric analysis (TGA). Both polymers degraded starting at 350 degreesC, according to a single mechanism for polyA and two distinct mechanisms for polyF. In addition, the isothermal TGA study of thermal ageing for 24 hours showed that both compounds were very stable at 250 degreesC (losses of mass less than 3%) and that polyF was more stable than polyA when heated between 350 and 550 degreesC. Degradation residues were analyzed by infrared-Fourier transform spectroscopy (FT-IR). Volatile organic compounds (VOC) released by pyrolysis were analyzed by pyrolysis/thermal desorption cold trap/gas chromatography/mass spectrometry. These methods enabled us to determine degradation mechanisms in the same temperature interval. The data showed that the major part of the degradation occurred in the cyclic ether, with breaks at cross-linking nodes and C-O bonds. Since the skeletons of the crosslinking nodes of both compounds were identical, the higher stability can be attributed to the presence of fluorine in its central hexafluorinated pivot, providing greater heat stability than the isopropyl pivot in polyA

Sulfate-reducing bacteria inhabiting natural corrosion depostis from marine steel structures

In the present study, investigations were conducted on natural corrosion deposits to better understand the role of sulfate-reducing bacteria (SRB) in the accelerated corrosion process of carbon steel sheet piles in port environments. We describe the abundance and diversity of total and metabolically active SRB within five natural corrosion deposits located within tidal or low water zone and showing either normal or accelerated corrosion. By using molecular techniques, such as quantitative real-time polymerase chain reaction, denaturing gel gradient electrophoresis, and sequence cloning based on 16S rRNA, dsrB genes, and their transcripts, we demonstrated a clear distinction between SRB population structure inhabiting normal or accelerated low-water corrosion deposits. Although SRB were present in both normal and accelerated low-water corrosion deposits, they dominated and were exclusively active in the inner and intermediate layers of accelerated corrosion deposits. We also highlighted that some of these SRB populations are specific to the accelerated low-water corrosion deposit environment in which they probably play a dominant role in the sulfured corrosion product enrichment

Heat stability and degradation of thermally stable prepolymers in a controlled atmosphere: III. Thermal homopolymerization cycle of dicyanate monomers and physicochemical characterization of the crosslinked system

International audienceMonitoring the homopolymerization of cyanate monomers during heat treatment shows that triazine rings formed during the 180 degreesC step. Oligomers were composed of 1 to 15 triazine rings. Analysis of compounds formed before the gel point revealed the presence of side products containing terminal phenolic functions: the phenol-cyanate (M-0-OH) and oligomers with one or two hydroxyl functions (M-1.2,...-OH). Kinetic and mechanistic monitoring during treatment at 210 degreesC in the solid state allowed the determination of the structure of the final system and the detection and quantification of unreacted cyanate functions. Kinetic and thermal studies in the temperature range of 100 to 220 degreesC showed that the homopolymerization of hexafluorobisphenol A dicyanate starts at a lower temperature and is slower than that of bisphenol A dicyanate. Thermogravimetric data showed that residual monomers volatilized between 150 and 300 degreesC, while the degradation of crosslinked products occurred between 400 and 600 degreesC and involved two distinct steps

Impact of a simulated oil spill on benthic phototrophs and nitrogen-fixing bacteria in mudflat mesocosms

International audienceCoastal and estuarine ecosystems are highly susceptible to crude oil pollution. Therefore, in order to examine the resilience of benthic phototrophs that are pivotal to coastal ecosystem functioning, we simulated an oil spill in tidal mesocosms consisting of intact sediment cores from a mudflat at the mouth of the Colne Estuary, UK. At day 21, fluorescence imaging revealed a bloom of cyanobacteria on the surface of oiled sediment cores, and the upper 1.5cm thick sediment had 7.2 times more cyanobacterial and 1.7 times more diatom rRNA sequences when treated with oil. Photosystem II operating efficiency (Fq′/Fm′) was significantly reduced in oiled sediments at day 7, implying that the initial diatom-dominated community was negatively affected by oil, but this was no longer apparent by day 21. Oil addition significantly reduced numbers of the key deposit feeders, and the decreased grazing pressure is likely to be a major factor in the increased abundance of both diatoms and cyanobacteria. By day 5 concentrations of dissolved inorganic nitrogen were significantly lower in oiled mesocosms, likely resulting in the observed increase in nifH-containing, and therefore potentially dinitrogen-fixing, cyanobacteria. Thus, indirect effects of oil, rather than direct inhibition, are primarily responsible for altering the microphytobenthos. © 2012 Society for Applied Microbiology and Blackwell Publishing Ltd