Effect of acidic industrial effluent release on microbial diversity and trace metal dynamics during resuspension of coastal sediment

Both industrial effluent discharge and the resuspension of contaminated marine sediments are important sources of trace metals in seawater which potentially affect marine ecosystems. The aim of this study was to evaluate the impact of the industrial wastewaters having acidic pH (2-3) and containing trace metals on microbial diversity in the coastal ecosystem of the Gulf of Gabes (Tunisia, southern Mediterranean Sea) subjected to resuspension events of marine sediments. Four trace elements (As, Cd, U, and V) were monitored during 10-day sediment resuspension experiments. The highest enrichment in the seawater dissolved phase was observed for Cd followed by U, V, and As. Cd remobilization was improved by indigenous microbial community, while U release was mainly abiotic. Acidic effluent addition impacted both trace metal distribution and microbial diversity, particularly that of the abundant phylum Bacteroidetes. Members of the order Saprospirales were enriched from sediment in natural seawater (initial pH > 8), while the family Flavobacteriaceae was favored by acidified seawater (initial pH < 8). Some Flavobacteriaceae members were identified as dominant species in both initial sediment and experiments with acidic wastewater, in which their relative abundance increased with increasing dissolved Cd levels. It could be therefore possible to consider them as bioindicators of metal pollution and/or acidification in marine ecosystems

Special issue of MERMEX project : recent advances in the oceanography of the Mediterranean Sea

The goal of this work is to investigate the spatial distribution and sources of dissolved aliphatic and poly cyclic aromatic hydrocarbons (AHs and PAHs), as well as their relationships with a series of biogeochemical parameters (total chlorophyll a, phaeopigment a, suspended particulate matter, particulate and dissolved organic carbon, and nutrients), in surface coastal waters of the Gulf of Gabes (Tunisia, Southern Mediterranean Sea). Samples were collected off the Northern and Southern coasts of Sfax city, as well as in the Gabes-Ghannouch area, from October-November 2014 and in March 2015. Total dissolved AH and PAH concentrations ranged from 0.02 to 6.314 mu g L-1 and from 8.9 to 197.8 ng L-1, respectively. These data suggest that this area has been moderate-to-highly impacted by hydrocarbons compared to other Mediterranean coastal environments. The highest AH concentrations were measured off of the Sfax Northern coast (near Ezzit wadi) and in the Gabes-Ghannouch area, whereas the highest PAH concentrations were recorded in the Sfax Southern coast (near commercial and fishing harbours and the Sidi Salem channel). Analysis of the AH molecular patterns reveals that low molecular weight (LMW) compounds in these samples are dominated by n-C-16, n-C-17 and n-C-18, which suggests that these samples feature high biogenic activity (in the form of bacteria or algae), and that high molecular weight (HMW) compounds display monomodal distributions centred on n-C-25 and n-C-26, which can be attributed to petrogenic inputs. The PAH molecular patterns are characterized by the dominance of LMW (2-3 rings) compounds and their alkylated homologues, which account for 90 +/- 7% of total PAHs. The observed PAH distribution and isomer ratios thus indicate the presence of major petrogenic contaminations. The concentrations of AHs, PAHs and dissolved organic carbon (DOC) do not correlate with each other, thus demonstrating that these three pools likely originated from different sources and subsequently underwent different processes in the Gulf of Gabes

Natural and anthropogenic particulate-bound aliphatic and polycyclic aromatic hydrocarbons in surface waters of the Gulf of Gabes (Tunisia, southern Mediterranean Sea)

Particulate-bound aliphatic and polycyclic aromatic hydrocarbons (AHs and PAHs) were investigated in the surface waters of the Gulf of Gabes (Tunisia, southern Mediterranean Sea). Samples were collected off the Sfax and Gabes-Ghannouch coasts. Concentrations in total resolved n-alkanes ranged from 0.03 to 3.2 mu g L-1, and concentrations in total parents + alkylated PAHs ranged from bdl to 108.6 ng L-1. The highest concentrations were recorded in the southern Sfax. AHs were mainly of biogenic origin with odd n-alkane predominance, although an anthropogenic contribution was also detected. The PAH molecular patterns revealed a mixed origin with the presence of low molecular weight and alkylated compounds, characteristic of uncombusted oil-derived products, and the presence of high molecular weight compounds, typical of combustion residues. Rainfall events induced an increase in PAH concentrations by a factor 1.5-23.5. The particle-water partition coefficients (K-oc) suggest that the partitioning of PAHs between the particulate and dissolved phases is driven by hydrophobicity and organic matter composition

Effect and removal of bisphenol A by two extremophilic microalgal strains (Chlorophyta)

The effects and the removal efficiency of bisphenol A (BPA) on two extremophilic Chlorophyta strains, an alkaliphilic Picocystis and a thermophilic Graesiella, were assessed. BPA was shown to inhibit the growth and photosynthesis of both species, but to a greater extent for Graesiella. The growth IC50 (4 days) was 32 mg L-1 for Graesiella and higher than 75 mg L-1 for Picocystis. Oxidative stress was induced in both strains when exposed to increasing BPA concentrations, as evidenced by increased malondialdehyde content. BPA exposure also resulted in an over-expression of antioxidant activities (ascorbate peroxidase, glutathione S-transferase and catalase) in Picocystis whereas they were repressed in Graesiella. Both species exhibited high BPA removal efficiency, reaching 72% for Picocystis and 52.6% for Graesiella at 25 mg L-1. BPA removal was mostly attributed to biodegradation for both species. Overall, according to its extended tolerance and its removal capacity, Picocystis appeared to be a promising species for the BPA bioremediation even at high contamination levels

Polycyclic aromatic hydrocarbon degradation and biosurfactant production by a newly isolated Pseudomonas sp. strain from used motor oil-contaminated soil

The aim of this study was to isolate and characterize a newly isolated bacterium, designated strain W10, a polycyclic aromatic hydrocarbon (PAHs) degrader and biosurfactant producer, belonged to Pseudomonas genus and closely related to Pseudomonas aeruginosa, with the 16 rRNA gene sequence similarity of 99.1%. Based on GC-MS analyses, it degraded around 80% of phenanthrene, used as the sole carbon and energy source, at an initial concentration of 200 mg l−1, after 30 days of incubation at 37 °C and 180 rpm, reducing the surface tension (ST) from 56.1 to 42 mN m−1 after 4 days of incubation. Furthermore, strain W10 utilized about 10%, 20%, 90%, and 99% of hexadecane (C16), pyrene, fluoranthene, and crude oil, respectively, after 30 days of incubation at 37 °C and 180 rpm. During the growth of strain W10 on phenanthrene and fluoranthene, some metabolites were identified, supporting the biodegradation pathways of the two PAHs. Interestingly, strain W10 showed also a significant potential to produce surface-active agents reducing the surface tension to 32 mN m−1 and reaching a production around 2 g l−1 after 48 h of incubation, in the presence of olive oil (1%,v/v) as substrate, at 37 °C and 180 rpm. Its biosurfactant, namely BSW10, showed an interesting emulsification activity and a high stability over a wide range of salinity (0–150 g l−1), temperature (0–100 °C), pH (2–12) and thus a promising abilities in used motor oil and crude oil removal from contaminated soils. Overall, these results provide evidence that strain W10 and its biosurfactant (BSW10) could be potential candidates for further bioremediation applications

Biochemical characterization, microbial diversity and biodegradability of coastal sediments in the Gulf of Gabès, Southern Mediterranean Sea

International audienceCoastal sediments are considered to be final receptacles for organic and inorganic contaminants. Characterizing those sediments and assessing their biodegradation potential have become a great challenge in recent years. In this study, the chemical composition, including the content in polycyclic aromatic hydrocarbons, the microbial community abundance and diversity (using culture-independent approaches targeting 16S rRNA genes), and the aerobic/anaerobic biodegradation potential of coastal sediments collected in the Sfax coastal area (Gulf of Gabès, Southern Mediterranean Sea) were investigated. The highest concentration of total polycyclic aromatic hydrocarbons (981 µg kg−1 dw) was recorded in Sidi Mansour harbor sediment, emphasized pyrogenic and petrogenic hydrocarbon sources. Organic matter, including total organic carbon, and the ultimate aerobic biodegradability, with 30% as the highest value in Sidi Salem channel sediment, were in a positive accordance with bacterial communities assigned within Actinobacteria, Clostridia and Flavobacteria classes. The correlation noticed between Thermocladium and Thermogladius genera and sulfate content explained that Sidi Mansour and PK4 sediments are located in terrestrial acid–sulfate areas. The highest cumulative methane produced with Marseille inoculum and Tunisian inoculum was recorded in Sidi Salem sediment and strongly correlated with methanogens among Methanobacteria, Methanococci and Methanomicobia classes showing the presence of industrial and municipal sources. The bioavailability of low and moderate polycyclic aromatic hydrocarbons in the current study may explain the occurrence of Methanobacterium which positively correlated with the anaerobic biodegradability using Tunisian inoculum with 50% as the highest value in Sidi Mansour sediment