Variation of oxygenation conditions on a hydrocarbonoclastic microbial community reveals Alcanivorax and Cycloclasticus ecotypes

Deciphering the ecology of marine obligate hydrocarbonoclastic bacteria (MOHCB) is of crucial importance for understanding their success in occupying distinct niches in hydrocarbon-contaminated marine environments after oil spills. In marine coastal sediments, MOHCB are particularly subjected to extreme fluctuating conditions due to redox oscillations several times a day as a result of mechanical (tide, waves and currents) and biological (bioturbation) reworking of the sediment. The adaptation of MOHCB to the redox oscillations was investigated by an experimental ecology approach, subjecting a hydrocarbon-degrading microbial community to contrasting oxygenation regimes including permanent anoxic conditions, anoxic/oxic oscillations and permanent oxic conditions. The most ubiquitous MOHCB, Alcanivorax and Cycloclasticus, showed different behaviors, especially under anoxic/oxic oscillation conditions, which were more favorable for Alcanivorax than for Cycloclasticus. The micro-diversity of 16S rRNA gene transcripts from these genera revealed specific ecotypes for different oxygenation conditions and their dynamics. It is likely that such ecotypes allow the colonization of distinct ecological niches that may explain the success of Alcanivorax and Cycloclasticus in hydrocarbon-contaminated coastal sediments during oil-spills

The variable influence of dispersant on degradation of oil hydrocarbons in subarctic deep-sea sediments at low temperatures (0-5 °C)

The microbial degradation of petroleum hydrocarbons at low temperatures was investigated in subarctic deep-sea sediments in th e Faroe Shetland Channel (FSC). The effect of the marine oil dispersant, Superdispersant 25 on hydrocarbon degradation was also examined. Sediments collected at 500 and 1000 m depth were spiked with a model oil containing 20 hydrocarbons and incubated at ambient temperature (5 and 0 °C, respectively) with and without marine dispersant. Treatment of sediments with hydrocarbons resulted in the enrichment of Gammaproteobacteria, and specifically the genera Pseudoalteromonas, Pseudomonas, Halomonas, and Cobetia. Hydrocarbon degradation was faster at 5 °C (500 m) with 65-89% of each component degraded after 50 days compared to 0-47% degradation at 0 °C (1000 m), where the aromatic hydrocarbons fluoranthene, anthracene, and Dibenzothiophene showed no degradation. Dispersant significantly increased the rate of degradation at 1000 m, but had no effect at 500 m. There was no statistically significant effect of Superdispersant 25 on the bacterial community structure at either station. These results show that the indigenous bacterial community in the FSC has the capacity to mitigate some of the effects of a potential oil spill, however, the effect of dispersant is ambiguous and further research is needed to understand the implications of its use

Impact of oil on bacterial community structure in bioturbated sediments

Oil spills threaten coastlines where biological processes supply essential ecosystem services. Therefore, it is crucial to understand how oil influences the microbial communities in sediments that play key roles in ecosystem functioning. Ecosystems such as sediments are characterized by intensive bioturbation due to burrowing macrofauna that may modify the microbial metabolisms. It is thus essential to consider the bioturbation when determining the impact of oil on microbial communities. In this study, an experimental laboratory device maintaining pristine collected mudflat sediments in microcosms closer to true environmental conditions - with tidal cycles and natural seawater - was used to simulate an oil spill under bioturbation conditions. Different conditions were applied to the microcosms including an addition of: standardized oil (Blend Arabian Light crude oil, 25.6 mg.g21 wet sediment), the common burrowing organism Hediste (Nereis) diversicolor and both the oil and H. diversicolor. The addition of H. diversicolor and its associated bioturbation did not affect the removal of petroleum hydrocarbons. After 270 days, 60% of hydrocarbons had been removed in all microcosms irrespective of the H. diversicolor addition. However, 16S-rRNA gene and 16S-cDNA T-RFLP and RT-PCR-amplicon libraries analysis showed an effect of the condition on the bacterial community structure, composition, and dynamics, supported by PerMANOVA analysis. The 16S-cDNA libraries from microcosms where H. diversicolor was added (oiled and un-oiled) showed a marked dominance of sequences related to Gammaproteobacteria. However, in the oiled-library sequences associated to Deltaproteobacteria and Bacteroidetes were also highly represented. The 16S-cDNA libraries from oiled-microcosms (with and without H. diversicolor addition) revealed two distinct microbial communities characterized by different phylotypes associated to known hydrocarbonoclastic bacteria and dominated by Gammaproteobacteria and Deltaproteobacteria. In the oiled-microcosms, the addition of H. diversicolor reduced the phylotype-richness, sequences associated to Actinobacteria, Firmicutes and Plantomycetes were not detected. These observations highlight the influence of the bioturbation on the bacterial community structure without affecting the biodegradation capacities

Response of Archaeal Communities to Oil Spill in Bioturbated Mudflat Sediments

cited By 17International audienceThe response of archaeal community to oil spill with the combined effect of the bioturbation activity of the polychaetes Hediste diversicolor was determined in mudflat sediments from the Aber-Benoît basin (Brittany, French Atlantic coast), maintained in microcosms. The dynamics of the archaeal community was monitored by combining comparative terminal restriction fragment length polymorphism (T-RFLP) fingerprints and sequence library analyses based on 16S rRNA genes and 16S cDNA. Methanogens were also followed by targeting the mcrA gene. Crenarchaeota were always detected in all communities irrespective of the addition of H. diversicolor and/or oil. In the presence of oil, modifications of archaeal community structures were observed. These modifications were more pronounced when H. diversicolor was added resulting in a more diverse community especially for the Euryarchaeota and Thaumarchaeota. The analysis of mcrA transcripts showed a specific structure for each condition since the beginning of the experiment. Overall, oiled microcosms showed different communities irrespective of H. diversicolor addition, while similar hydrocarbon removal capacities were observed

Methanogenic octadecene degradation by syntrophic enrichment culture from brackish sediments

A microbial enrichment culture from brackish sediments was able to grow on octadec-1-ene (an unsaturated aliphatic hydrocarbon) as sole source of carbon and energy, under methanogenic conditions. Octadecene degradation is stopped either when bromoethanesulfonic acid, a selective inhibitor of methanogenesis is introduced, or when hydrogen is introduced. In the presence of bromoethanesulfonic acid, the degradation is restored by the addition of a hydrogenotrophic sulfate-reducing microorganism with sulfate. Results of molecular biodiversity, which revealed the presence of bacteria as well as of acetoclastic and hydrogenotrophic methanogens, are consistent with a syntrophic degradation involving Bacteria and Archaea. This is the first demonstration of syntrophic alkene degradation by microbial communities, showing that syntrophy is more widespread than we could have thought so far. These results highlight the need for a better understanding of microbial interactions and their role in the organic-matter degradation in polluted environments

New Insights Into Bacterial Wax Ester Biosynthesis, Natural Occurrence And Adaptive Role In Anaerobic Environments

International audienc

Climate change influences chlorophylls and bacteriochlorophylls metabolism in hypersaline microbial mat

International audienceThis study aimed to determine the effect of the climatic change on the phototrophic communities of hypersaline microbial mats. Ocean acidification and warming were simulated alone and together on microbial mats placed into mesocosms. As expected, the temperature in the warming treatments increased by 4 °C from the initial temperature. Surprisingly, no significance difference was observed between the water pH of the different treatments despite of a decrease of 0.4 unit pH in the water reserves of acidification treatments. The salinity increased on the warming treatments and the dissolved oxygen concentration increased and was higher on the acidification treatments. A total of 37 pigments were identified belonging to chlorophylls, carotenes and xanthophylls families. The higher abundance of unknown chlorophyll molecules called chlorophyll derivatives was observed in the acidification alone treatment with a decrease in chlorophyll a abundance. This change in pigmentary composition was accompanied by a higher production of bound extracellular carbohydrates but didn't affect the photosynthetic efficiency of the microbial mats. A careful analysis of the absorption properties of these molecules indicated that these chlorophyll derivatives were likely bacteriochlorophyll c contained in the chlorosomes of green anoxygenic phototroph bacteria. Two hypotheses can be drawn from these results: 1/ the phototrophic communities of the microbial mats were modified under acidification treatment leading to a higher relative abundance of green anoxygenic bacteria, or 2/ the highest availability of CO2 in the environment has led to a shift in the metabolism of green anoxygenic bacteria being more competitive than other phototrophs

Responses of a free-living benthic marine nematode community to bioremediation of a PAH mixture

The objectives of this study were (1) to assess the responses of benthic nematodes to a polycyclic aromatic hydrocarbon (PAH) contamination and (2) to test bioremediation techniques for their efficiency in PAH degradation and their effects on nematodes. Sediments with their natural nematofauna communities from Bizerte lagoon (Tunisia) were subjected to a PAH mixture (100 ppm) of phenanthrene, fluoranthene, and pyrene during 30 days. Nematode abundance and diversity significantly decreased, and the taxonomic structure was altered. Results from multivariate analyses of the species abundance data revealed that PAH treatments were significantly different from the control. Spirinia parasitifera became the dominant species (70 % relative abundance) and appeared to be an "opportunistic" species to PAH contamination while Oncholaimus campylocercoides and Neochromadora peocilosoma were strongly inhibited. Biostimulation (addition of mineral salt medium) and bioaugmentation (inoculation of a hydrocarbonoclastic bacterium) were used as bioremediation techniques. Bioremediation treatments enhanced degradation of all three PAHs, with up to 96 % degradation for phenanthrene resulting in a significant stimulation of nematode abundance relative to control microcosms. Nevertheless, these treatments, especially the biostimulation provoked a weak impact on the community structure and diversity index relative to the control microcosms suggesting their feasibility in biorestoration of contaminated sediments

Microbial community responses to bioremediation treatments for the mitigation of low-dose anthracene in marine coastal sediments of Bizerte lagoon (Tunisia)

The main goals of this study were to investigate (1) the behavior of microbial communities in response to low-dose bioavailable anthracene addition in lightly contaminated sediment from Bizerte Lagoon and (2) the effects of bioremediation treatments on microbial biomass, activity, and community structure. Sediment microcosms amended with 1 ppm anthracene were incubated in triplicate during 30 days. Biostimulation (addition of nitrogen and phosphorus fertilizer) and bioaugmentation (inoculation of a hydrocarbonoclastic bacterium) were used as bioremediation treatments. Bacterial biomass was estimated using flow cytometry. Sediment oxygen consumption was measured with oxygen microelectrodes. Bacterial community structure was assessed by molecular fingerprints (terminal restriction fragment length polymorphism; T-RFLP) analysis. Anthracene contamination resulted in a significant reduction of bacterial abundance with an impact on cell integrity. Concomitantly, sediment oxygen consumption was strongly inhibited. Correspondence analysis on T-RFLP data indicated that bacterial community structures from anthracene-contaminated microcosms were different from that of the control. Interestingly, the changes observed in microbial biomass, structure, and activities as a result of anthracene contamination were not alleviated even with the use of biostimulation and combination of biostimulation and bioaugmentation strategy for anthracene bioremediation. Nevertheless, both treatment methods resulted in different community structures relative to the contaminated and control microcosms with the appearance of distinct populations. Anthracene spiking severely affected microbial communities, suggesting dominance of nontolerant populations in this lightly-contaminated sediment. Although biostimulation and/or bioaugmentation treatments did not alleviate the anthracene toxic effects, the changes observed in microbial population and structure suggest that the proposed treatments might be promising to promote bacterial growth. Further works are still required to propose a more efficient strategy to stimulate biodegradation that takes into account the complex interactions between species for resource access