Impact of a biorepair treatment on the diversity of calcifying bacterial communities at the surface of cracked concrete walls

International audienceChanges in the diversity of indigenous calcifying bacterial communities were determined before and after 1 year of biorepair treatment applied on indoor micro-cracked concrete walls. The biotreatment was based on the formation of an organo-mineral coating generated by Alkalihalobacillus pseudofirmus cultured in the presence of calcium lactate. Before and after the biotreatment, the calcifying bacterial strains belonging to either Firmicutes or Actinobacteria phylum were dominant depending on the sampling area. Nevertheless, the proportion of the calcifying Bacillus, Brachybacterium, Microbacterium, and Rhodococcus genera changed. These bacterial strains were likely to participate in the effectiveness of the biotreatment. Isolated bacteria of Microbacterium and Rhodococcus genera reported interesting calcifying capacity associated to microbial growth rates greater than the one observed for Alkalihalobacillus pseudofirmus. A bacterial consortium containing Alkalihalobacillus pseudofirmus, Rhodococcus cercidiphylli, and Microbacterium schleiferi demonstrated an improved calcifying capacity. Consequently, using a bacterial consortium instead of a single strain is an efficient way to improve the robustness of the biorepair treatment. Key points: • Indigenous calcifying bacteria mainly belonged to Firmicutes and Actinobacteria • Microbacterium and Rhodococcus reported the quickest growth rate with calcium lactate • A bacterial consortium with improved calcifying capacity is propose

Microbial degradation of hydrophobic emerging contaminants from marine sediment slurries (Capbreton Canyon) to pure bacterial strain

Despite emerging contaminants (ECs) are more and more monitored in environmental matrices, there is still lack of data in marine ecosystems, especially on their fate and degradation potentials. In this work, for the first time, the degradation potential of synthetic musks (galaxolide and tonalide), UV filters (padimate O and octo-crylene) and a pharmaceutical compound (carbamazepine) was studied in marine sediment samples, under laboratory conditions using sediment slurry incubations under biotic and abiotic conditions. Minimum half life times under biotic conditions were found at 21 days, 129 days and 199 days for padimate O, galaxolide and carbamazepine, respectively. Enrichments conducted under anoxic and oxic conditions demonstrated that degradations after one month of incubation either under both biotic and abiotic conditions were limited under anoxic conditions compared to oxic conditions for all the contaminants. Novel aerobic bacteria, able to degrade synthetic musks and UV filters have been isolated. These novel strains were mainly related to the Genus Bacillus. Based on these results, the isolated strains able to degrade such ECs, can have a strong implication in the natural resilience in marine environment, and could be used in remediation processes

Draft genome sequence of desulfovibrio BerOc1, a mercury-methylating Strain

Desulfovibrio BerOc1 is a sulfate-reducing bacterium isolated from the Berre lagoon (French Mediterranean coast). BerOc1 is able to methylate and demethylate mercury. The genome size is 4,081,579 bp assembled into five contigs. We identified the hgcA and hgcB genes involved in mercury methylation, but not those responsible for mercury demethylation

Distribution of sulfate-reducing communities from estuarine to marine bay waters

Estuaries are highly dynamic ecosystems in which freshwater and seawater mix together. Depending on tide and river inflows, particles originating from rivers or from the remobilization of sediments accumulate in the water column. Due to the salinity gradient and the high heterotrophic activity in the estuarine plume, hypoxic and anoxic microniches may form in oxygenated waters, sustaining favorable conditions for resuspended anaerobic microorganisms. In this context, we tested the hypothesis that anaerobic sulfate-reducing prokaryotes may occur in the water column of the Adour River. Using 16S ribosomal RNA (rRNA) and dsrAB-based terminal restriction fragment length polymorphism (T-RFLP) techniques, we characterized total prokaryotic and sulfate-reducing communities along a gradient from estuarine to marine bay waters.[br/] Sulfate-reducing prokaryotes were further characterized by the description of dsrB genes and the cultivation of sulfidogenic anaerobic microorganisms. As a result, physical-chemical parameters had a significant effect on water bacterial diversity and community structure along the studied gradient. The concentration of cultured sulfidogenic microorganisms ranged from 1 to 60 x 10(3) cells l(-1) in the water column. Sulfate-reducing prokaryotes occurring in estuarine waters were closely related to microorganisms previously detected in freshwater sediments, suggesting an estuarine origin, mainly by the remobilization of the sediments. In the marine bay station, sediment-derived sulfate-reducing prokaryotes were not cultured anymore, probably due to freshwater dilution, increasing salinity and extended oxic stress.[br/] Nevertheless, isolates related to the type strain Desulfovibrio oceani were cultured from the diluted plume and deep marine waters, indicating the occurrence of autochthonous sulfate-reducing bacteri

Impact of Bioaugmentation on the Bioremediation of Saline-Produced Waters Supplemented with Anaerobic Digestate

Bioremediation of produced waters has been widely investigated in the last decades. More recently, microalgae-based treatments have been developed to produce biomass. The objective of this study was to determine, at lab scale, the remediation efficiency of three origin of microorganisms: a consortium of three halotolerant and halophilic microalgae and their associated bacteria, bacteria from liquid digestate, and aromatic-degrading bacteria selected to perform bioaugmentation. The medium was composed of artificial oil-produced water and seawater, and contained nutrients from liquid digestate. In order to identify what plays a role in nitrogen, chemical oxygen demand, and aromatics compounds elimination, and to determine the effectiveness of bioaugmentation to treat this mix of waters, 16S rRNA analyses were performed. Combination of microorganisms from different origins with the selected aromatic-degrading bacteria were also realized, to determine the effectiveness of bioaugmentation to treat these waters. Each population of microorganisms achieved similar percentage of removal during the biological treatment, with 43–76%, 59–77%, and 86–93% of elimination for ammonium, chemical oxygen demand, and aromatic compounds (with 50% of volatilization), respectively, after 7 days, and up to with 100%, 77%, and 99% after 23 days, demonstrating that in the case of this produced water, bioaugmentation with the specialized aromatic-degrading bacteria had no significant impact on the treatment. Regarding in detail the populations present and active during the tests, those from genus Marinobacter always appeared among the most active microorganisms, with some strains of this genus being known to degrade aromatic compounds

Influence of Macrophyte and Gut Microbiota on Mercury Contamination in Fish: A Microcosms Study

International audienceThe freshwater lakes of southwestern France are subject to the development of invasive macrophytes which are associated with mercury (Hg) contamination of the food web. The aim of this study was to determine the bioavailability of methylmercury (MeHg) produced by plant roots in aquatic ecosystems. A microcosm experiment was performed using isotopically enriched inorganic Hg at environmental concentrations (1 μg 199IHg L-1). For all conditions, total Hg in fish as well as Hg species associated with different compartments (water, sediments, plant roots, fish) were analyzed by gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS). In addition, sediment, plants, and fish gut microbiota were studied by MiSEQ sequencing. Some strains were isolated and tested for their ability to methylate Hg. The results revealed 199MeHg production in plant roots and the presence of this form in fish (tissues and gut), highlighting a MeHg trophic transfer. Moreover, methylator bacteria were identified from the gut contents of the fish when they were in the presence of plants. Some of them were related to bacteria found in the plant roots. On the basis of these results, the transfer of MeHg and bacteria from plants to fish is highlighted; in addition, Hg methylation is strongly suspected in the fish gut, potentially increasing the Hg bioaccumulation

In Vivo Mercury (De)Methylation Metabolism in Cephalopods under Different p CO 2 Scenarios

International audienceThis work quantified the accumulation efficiencies of Hg in cuttlefish, depending on both organic (MeHg) and inorganic (Hg(II)) forms, under increased pCO2 (1600 μatm). Cuttlefish were fed with live shrimps injected with two Hg stable isotopic tracers (Me202Hg and 199Hg(II)), which allowed for the simultaneous quantification of internal Hg accumulation, Hg(II) methylation, and MeHg demethylation rates in different organs. Results showed that pCO2 had no impact on Hg bioaccumulation and organotropism, and both Hg and pCO2 did not influence the microbiota diversity of gut and digestive gland. However, the results also demonstrated that the digestive gland is a key organ for in vivo MeHg demethylation. Consequently, cuttlefish exposed to environmental levels of MeHg could exhibit in vivo MeHg demethylation. We hypothesize that in vivo MeHg demethylation could be due to biologically induced reactions or to abiotic reactions. This has important implications as to how some marine organisms may respond to future ocean change and global mercury contamination

Linking Microbial Activities and Low-Molecular-Weight Thiols to Hg Methylation in Biofilms and Periphyton from High-Altitude Tropical Lakes in the Bolivian Altiplano

International audienceThe sources and factors controlling concentrations of monomethylmercury (MMHg) in aquatic ecosystems need to be better understood. Here, we investigated Hg transformations in sediments, periphyton associated with green algae's or aquatic plants, and benthic biofilms from the Lake Titicaca hydrosystem and compared them to the occurrence of active methylating microorganisms and extracellular Hg ligands. Intense Hg methylation was found in benthic biofilms and green algae's periphyton, while it remained low in sediments and aquatic plants' periphyton. Demethylation varied between compartments but remained overall in the same range. Hg methylation was mainly carried out by sulfate reducers, although methanogens also played a role. Its variability between compartments was first explained by the presence or absence of the hgcAB genes. Next, both benthic biofilm and green algae's periphyton exhibited a great diversity of extracellular low-molecular-weight (LMW) thiols (13 or 14 compounds) present at a range of a few nmol L−1 or μmol L−1 but clearly dominated by cysteine and 3-mercaptopropionic acid. Hg methylation was overall positively correlated to the total thiol concentrations, albeit to different extents according to the compartment and conditions. This work is the first examining the interplay between active methylating bacterial communities and extracellular ligands in heterotrophic biofilms and supports the involvement of LMW thiols in Hg methylation in real aquatic systems

Extreme Arsenic Bioaccumulation Factor Variability in Lake Titicaca, Bolivia

International audienceLatin America, like other areas in the world, is faced with the problem of high arsenic (As) background in surface and groundwater, with impacts on human health. We studied As biogeochemical cycling by periphyton in Lake titicaca and the mine-impacted Lake Uru Uru. As concentration was measured in water, sediment, totora plants (Schoenoplectus californicus) and periphyton growing on stems, and As speciation was determined by X-ray absorption spectroscopy in bulk and eDtA-extracted periphyton. Dissolved arsenic was between 5.0 and 15 μg L −1 in Lake Titicaca and reached 78.5 μg L −1 in Lake Uru Uru. As accumulation in periphyton was highly variable. We report the highest As bioaccumulation factors ever measured (BAFs periphyton up to 245,000) in one zone of Lake Titicaca, with As present as As(V) and monomethyl-As (MMA(V)). Non-accumulating periphyton found in the other sites presented BAFs periphyton between 1281 and 11,962, with As present as As(III), As(V) and arsenosugars. DNA analysis evidenced several taxa possibly related to this phenomenon. Further screening of bacterial and algal isolates would be necessary to identify the organism(s) responsible for As hyperaccumulation. Impacts on the ecosystem and human health appear limited, but such organisms or consortia would be of great interest for the treatment of As contaminated water. The arsenic (As) geogenic background of surface and groundwater is naturally high in South America, predominantly originating from young volcanic rocks and their weathering products in arid oxidizing conditions 1-4. As a result, about 4.5 million people in South America are chronically exposed to high levels of As (>50 µg L −1) 5 , and certain Andean populations have developed a unique capacity to adapt to As toxicity 6,7. Concerning Andean lakes, extreme As concentrations are observed in hypersaline lakes colonized by extremophile bacterial communities 8 , and lower but still significant concentrations are observed in other, less saline lakes, which are major freshwater resources 5. In many areas of the Altiplano, mining and smelting activities add to natural rock weathering processes in the As budget 9. The biogeochemical cycling of As has been studied in freshwater and marine ecosystems, and in hypersaline environments, but its trophic transfer and speciation in living organisms mainly concerns the marine environment and As contaminated freshwater systems 10. In the high altitude lakes of the Andean Altiplano (above 3500 m asl), shallow zones (<2 m) are colonized by totoras (Schoenoplectus californicus, syn Scirpus californicus). These macrophytes were used for construction purposes in traditional Andean culture. Nowadays, they are mainly used as cattle fodder and have been tested successfully in constructed wetlands in North America for the removal of metals (Zn, Cu, Cd, Pb) and nutrients from wastewater 11-14. The filtration potential of wetland plants does not rely on absorption by the plant, but on physico-chemical and biologically driven processes taking place on submerged stems and in the rhizosphere 15,16. In particular, the periphyton, an assemblage of algae and bacteria forming

Diurnal variability and biogeochemical reactivity of mercury species in an extreme high-altitude lake ecosystem of the Bolivian Altiplano

International audienceAbstr act Methylation and demethylation represent major transformation pathways regulating the net production of methylmercury (MMHg). Very few studies have documented Hg reactivity and transformation in extreme high-altitude lake ecosystems. Mercury (Hg) species concentrations (IHg, MMHg, Hg°, and DMHg) and in situ Hg methylation (M) and MMHg demethylation (D) potentials were determined in water, sediment, floating organic aggregates, and periphyton compartments of a shallow productive Lake of the Bolivian Altiplano (Uru Uru Lake, 3686 m). Samples were collected during late dry season (October 2010) and late wet season (May 2011) at a north (NS) and a south (SS) site of the lake, respectively. Mercury species concentrations exhibited significant diurnal variability as influenced by the strong diurnal biogeochemical gradients. Particularly high methylated mercury concentrations (0.2 to 4.5 ng L −1 for MMHg T) were determined in the water column evidencing important Hg methylation in this ecosystem. Methylation and D potentials range were, respectively, <0.1–16.5 and <0.2–68.3 % day −1 and were highly variable among compartments of the lake, but always higher during the dry season. Net Hg M indicates that the influence of urban and mining effluent (NS) promotes MMHg pro duction in both water (up to 0.45 ng MMHg L −1 day −1) and sediment compartments (2.0 to 19.7 ng MMHg g −1 day −1). While the sediment compartment appears to represent a major source of MMHg in this shallow ecosystem, floating organic aggregates (dry season, SS) and Totora's periphyton (wet season, NS) were found to act as a significant source (5.8 ng MMHg g −1 day −1) and a sink (−2.1 ng MMHg g −1 day −1) of MMHg, respectively. This work demonstrates that high-altitude productive lake ecosystems can promote MMHg formation in various compartments supporting recent observations of high Hg contents in fish and water birds