Bacterial community response to petroleum contamination and nutrient addition in sediments from a temperate salt marsh

Response of the soil microbial community to petroleum hydrocarbon stress shows a threshold effect: research on aged realistic contaminated fields

Introduction

Microbes play key roles in maintaining soil ecological functions. Petroleum hydrocarbon contamination is expected to affect microbial ecological characteristics and the ecological services they provide. In this study, the multifunctionalities of contaminated and uncontaminated soils in an aged petroleum hydrocarbon-contaminated field and their correlation with soil microbial characteristics were analyzed to explore the effect of petroleum hydrocarbons on soil microbes.

Methods

Soil physicochemical parameters were determined to calculate soil multifunctionalities. In addition, 16S high-throughput sequencing technology and bioinformation analysis were used to explore microbial characteristics.

Results

The results indicated that high concentrations of petroleum hydrocarbons (565-3,613 mg•kg^-1, high contamination) reduced soil multifunctionality, while low concentrations of petroleum hydrocarbons (13-408 mg•kg^-1, light contamination) might increase soil multifunctionality. In addition, light petroleum hydrocarbon contamination increased the richness and evenness of microbial community (p < 0.01), enhanced the microbial interactions and widened the niche breadth of keystone genus, while high petroleum hydrocarbon contamination reduced the richness of the microbial community (p < 0.05), simplified the microbial co-occurrence network, and increased the niche overlap of keystone genus.

Conclusion

Our study demonstrates that light petroleum hydrocarbon contamination has a certain improvement effect on soil multifunctionalities and microbial characteristics. While high contamination shows an inhibitory effect on soil multifunctionalities and microbial characteristics, which has significance for the protection and management of petroleum hydrocarbon-contaminated soil.

The Effects of Oil and Gas Produced Water on Soil Bacterial Community Structure in the Arid Desert Area

The safe utilization and risk assessment of produced water (PW) from oil and gas fields for desert irrigation have received increasing attention in recent years. In this context, this study aimed to analyze structural changes in soil bacterial community, and assess the environmental impact of PW discharge and irrigation over time. High-throughput sequencing technology was employed to examine the structure of the soil bacterial community in the constructed wetland and its surrounding desert vegetation irrigation region where PW was released for a considerable amount of time (30 years). The results revealed that long-term discharge of PW and irrigation significantly reduced the abundance of the soil bacterial community but did not significantly alter the richness and diversity of the soil bacterial community. Proteobacteria was the dominant bacterial phyla in soil, but in irrigated and drained areas, the dominant bacterial phyla changed from Alphaproteobacteria to Gammaproteobacteria, the Firmicutes abundance was significantly reduced.

Bacterial assemblage in Mediterranean salt marshes: Disentangling the relative importance of seasonality, zonation and halophytes

Salt marshes gather a high diversity of prokaryotes across their environmental gradients. Most of this diversity and the factors determining their community assemblage are unknown. We massively sequenced a portion of the 16S gene to characterize the diversity of prokaryotes in soils from a salt marsh in Río Piedras, Southern Spain. We sampled in the four seasons, and in five plots dominated by a different halophyte (Spartina maritima, S. densiflora, Salicornia ramosissima, Arthrocaulon macrostachyum and Atriplex portulacoides) growing under different environmental conditions and representing different stages in the marsh ecological succession. Soil was sampled in their rhizosphere and adjacent bulk soil. We report the effects of different factors explaining prokaryotic beta diversity in the marsh: zonation (50 %), seasonality (14 %), and halophyte rhizosphere (7 %). Proteobacteria and Bacteroidota were the most abundant phyla. Firmicutes had a peak in winter and Desulfobacterota with other bacteria involved in sulfur cycling were abundant in the low marsh plots from S. maritima. Alpha diversity was highest in spring and decreased in winter. We detected a marked phylogenetic turnover between seasons and in rhizospheric soil respect to adjacent bulk soil for most pairwise comparisons. The effect of halophyte on its rhizosphere was species-specific, being S. maritima the species with more differentiated taxa between rhizosphere versus surrounding bulk soil. Our work highlights how the complex interaction between marsh zonation, seasonality and rhizosphere, onsets processes structuring bacterial community assemblage in salt marsh soils.

Impacts of groundwater level fluctuation on soil microbial community, alkane degradation efficiency and alkane-degrading gene diversity in the critical zone: Evidence from an accelerated water table fluctuation simulation

Petroleum hydrocarbons are hazardous to ecosystems and human health, commonly containing n-alkanes and polycyclic aromatic hydrocarbons. Previous researches have studied alkane degraders and degrading genes under aerobic or anaerobic conditions, but seldom discussed them in the intermittent saturation zone which is a connective area between the vadose zone and the groundwater aquifer with periodic alteration of oxygen and moisture. The present study investigated the difference in alkane degradation efficiency, bacterial community, and alkane degrading gene diversity in aerobic, anaerobic, and aerobic-anaerobic fluctuated treatments. All biotic treatments achieved over 90% of n-alkane removal after 120 days of incubation. The removal efficiencies of n-alkanes with a carbon chain length from 16 to 25 were much higher in anaerobic scenarios than those in aerobic scenarios, explained by different dominant microbes between aerobic and anaerobic conditions. The highest removal efficiency was found in fluctuation treatments, indicating an accelerated n-alkane biodegradation under aerobic-anaerobic alternation. In addition, the copy numbers of the 16S rRNA gene and two alkB genes (alkB-P and alkB-R) declined dramatically when switched from aerobic to anaerobic scenarios and oppositely from anaerobic to aerobic conditions. This suggested that water level fluctuation could notably change the presence of aerobic alkane degrading genes. Our results suggested that alkane degradation efficiency, soil microbial community, and alkane-degrading genes were all driven by water level fluctuation in the intermittent saturation zone, helping better understand the effects of seasonal water table fluctuation on the biodegradation of petroleum hydrocarbons in the subsurface environment.

Response of soil microbial communities to petroleum hydrocarbons at a multi-contaminated industrial site in Lanzhou, China

Total petroleum hydrocarbon (TPH) contamination poses threats to ecological systems and human health. Many studies have reported its negative impacts on soil microbes, but limited information is known about microbial change and response to multiple TPH contamination events. In this study, we investigated TPH contamination level, microbial community structure and functional genes at a multi-contaminated industrial site in Lanzhou, where a benzene spill accident caused the drinking water crisis in 2014. TPHs distribution in soils and groundwater indicated multiple TPH contamination events in history, and identified the spill location where high TPH level (6549 mg kg^-1) and high ratio of low-molecular-weight TPHs (>80%) were observed. In contrast, TPH level was moderate (349 mg kg^-1) and the proportion of low-molecular-weight TPHs was 44% in soils with a long TPH contamination history. After the spill accident, soil bacterial communities became significant diverse (p = 0.047), but the dominant microbes remained the same as Pseudomonadaceae and Comamonadaceae. The abundance of hydrocarbon-degradation related genes increased by 10-1000 folds at the site where the spill accident occurred in multi-contaminated areas and was significantly related to 2-ring PAHs. Such changes of microbial community and hydrocarbon-degradation related genes together indicated the resilience of soil indigenous microbes toward multiple contamination events. Our results proved the significant change of bacterial community and huge shift of hydrocarbon-degradation related genes after the spill accident (multiple contamination events), and provided a deep insight into microbial response at industrial sites with a long period of contamination history.

The Widespread Use of Nanomaterials: The Effects on the Function and Diversity of Environmental Microbial Communities

In recent years, as an emerging material, nanomaterials have rapidly expanded from laboratories to large-scale industrial productions. Along with people's productive activities, these nanomaterials can enter the natural environment of soil, water and atmosphere through various ways. At present, a large number of reports have proved that nanomaterials have certain toxic effects on bacteria, algae, plants, invertebrates, mammalian cell lines and mammals in these environments, but people still know little about the ecotoxicology of nanomaterials. Most relevant studies focus on the responses of model strains to nanomaterials in pure culture conditions, but these results do not fully represent the response of microbial communities to nanomaterials in natural environments. Over the years, the effect of nanomaterials infiltrated into the natural environment on the microbial communities has become a popular topic in the field of nano-ecological environment research. It was found that under different environmental conditions, nanomaterials have various effects on the microbial communities. The medium; the coexisting pollutants in the environment and the structure, particle size and surface modification of nanomaterials may cause changes in the structure and function of microbial communities. This paper systematically summarizes the impacts of different nanomaterials on microbial communities in various environments, which can provide a reference for us to evaluate the impacts of nanomaterials released into the environment on the microecology and has certain guiding significance for strengthening the emission control of nanomaterials pollutants.

The potential of saltmarsh halophytes for phytoremediation of metals and persistent organic pollutants: An Australian perspective

Persistent organic and inorganic pollutants are among the most concerning pollutants in Australian estuaries due to their persistent, ubiquitous, and potentially toxic nature. Traditional methods of soil remediation often fall short of practical implementation due to high monetary investment, environmental disturbance, and potential for re-contamination. Phytoremediation is gaining traction as an alternative, or synergistic mechanism of contaminated soil remediation. Phytoremediation utilises plants and associated rhizospheric microorganisms to stabilise, degrade, transform, or remove xenobiotics from contaminated mediums. Due to their apparent cross-tolerance to salt, metals, and organic contaminants, halophytes have shown promise as phytoremediation species. This review examines the potential of 93 species of Australian saltmarsh halophytes for xenobiotic phytoremediation. Considerations for the practical application of phytoremediation in Australia are discussed, including mechanisms of enhancement, and methods of harvesting and disposal. Knowledge gaps for the implementation of phytoremediation in Australian saline environments are identified, and areas for future research are suggested.

Effect of petroleum hydrocarbon pollution levels on the soil microecosystem and ecological function

Petroleum hydrocarbon pollution is a global problem. However, the effects of different petroleum pollution levels on soil microbial communities and ecological functions are still not clear. In this study, we analyzed the changes in microbial community structures and carbon and nitrogen transformation functions in oil-contaminated soils at different concentrations by chemical analysis, high-throughput sequencing techniques, cooccurrence networks, and KEGG database comparison functional gene annotation. The results showed that heavy petroleum concentrations (petroleum concentrations greater than 20,000 mg kg^-1) significantly decreased soil microbial diversity (p = 0.01), soil microbiome network complexity, species coexistence patterns, and prokaryotic carbon and nitrogen fixation genes. In medium petroleum contamination (petroleum concentrations of between 4000 mg kg^-1 and 20,000 mg kg^-1), microbial diversity (p > 0.05) and carbon and nitrogen transformation genes showed no evident change but promoted species coexistence patterns. Heavy petroleum contamination increased the Proteobacteria phylum abundance by 3.91%-57.01%, while medium petroleum contamination increased the Actinobacteria phylum abundance by 1.69%-0.26%. The results suggested that petroleum concentrations played a significant role in shifting soil microbial community structures, ecological functions, and species diversities.

Oil degradation and variation of microbial communities in contaminated soils induced by different bacterivorous nematodes species

Oil pollution poses a great threat to environments and makes the remediation of oil-contaminated soils an urgent task. Microorganisms are the main biological factor for oil removal in the environment but microbial remediation is greatly affected by environmental factors. For our research, we inoculated three species of bacterivorous nematodes into oil-contaminated soil to explore how bacterivorous nematodes affect soil microbial activities and community structure in contaminated soil, as well as how efficiently different nematodes remove oil pollution from the soil. Six treatments were set in this experiment: sterilized oil-contaminated soil (SOC); nematode-free soil (S); oil-contaminated soil (OC); oil-contaminated soil + Caenorhabditis elegans (OCN1); oil-contaminated soil + Cephalobus persegnis (OCN2); oil-contaminated soil + Rhabditis marina (OCN3) for a 168-day incubation experiment. After the experiment was done, the oil contents in SOC, OC, OCN1, OCN2, and OCN3 were reduced by 6.5%, 32.3%, 38.2%, 42.8%, and 40.2%, respectively, compared with the beginning of the experiment. The amount of phospholipid fatty acids (PLFAs) of Gram-negative bacteria in OC, OCN1, OCN2, and OCN3 was increased by 50.9%, 43.4%, 37.7%, and 47.9%, respectively, compared with that of S. During the 168-day incubation period, the maximum growth of the number of nematodes in OCN1, OCN2, and OCN3 compared with the initial number of the nematodes were 2.25-, 1.52-, and 1.65-fold, respectively. The amount of oil residue in the contaminated soil negatively correlated with the populations of nematodes, total microorganisms, Gram-negative bacteria, actinomycetes, and eukaryotes. Thus, oil pollution increased the number of Gram-negative bacteria, decreased the ratio of Gram-positive bacteria/Gram-negative bacteria and Fungi/Bacteria significantly, and altered the community structure of soil microorganisms. Each species of bacterivorous nematodes has got its unique effect on the microbial activity and community structure in oil contaminated soils, but those tested can promote oil degradation and thus improve the environment of oil contaminated soils.

Occurrence and distribution of PAHs and microbial communities in nearshore sediments of the Knysna Estuary, South Africa

This study investigated the polycyclic aromatic hydrocarbons (PAHs) occurrence, and their impact on the microbial community and PAH-degrading genera and genes in the Knysna Estuary of South Africa. The results reveal that the estuary exhibits low PAH levels (114.1-356.0 ng g^-1). Ignavibacteriae and Deferribacteres, as well as Proteobacteria and Bacteroidetes, are keystone phyla. Among measured environmental factors, total organic carbon (TOC), nutrients such as nitrite and nitrate, metals as Al, Cr, Cu, Ni, Pb and Zn, and environmental properties (pH and salinity) are primary contributors to structuring the bacterial community assemblage. The abundance of alpha subunit genes of the PAH-ring hydroxylating dioxygenases (PAH-RHDα) of Gram-negative bacteria lies in the range of (2.0-4.2) × 10⁵ copies g^-1, while that of Gram-positive bacteria ranges from 3.0 × 10⁵ to 1.3 × 10⁷ copies g^-1. The PAH-degrading bacteria account for up to 0.1% of the bacterial community and respond mainly to nitrate, TOC and salinity, while PAHs at low concentration are not significant influencing factors. PAH degraders such as Xanthomonadales, Pseudomonas, and Mycobacterium, which play a central role in PAH-metabolization coupled with other biogeochemical processes (e.g. iron cycling), may contribute to maintaining a healthy estuarine ecosystem. These results are important for developing appropriate utilization and protection strategies for pristine estuaries worldwide.

Bacterial community response to petroleum contamination in brackish tidal marsh sediments in the Yangtze River Estuary, China

The brackish tidal marsh in the Baimaosha area of the Yangtze River Estuary was severely contaminated by 400 tons of heavy crude petroleum from a tanker that sank in December 2012. The spill accident led to severe environmental damage owing to its high toxicity, persistence and wide distribution. Microbial communities play vital roles in petroleum degradation in marsh sediments. Therefore, taxonomic analysis, high-throughput sequencing and 16S rRNA functional prediction were used to analyze the structure and function of microbial communities among uncontaminated (CK), lightly polluted (LP), heavily polluted (HP), and treated (TD) sediments. The bacterial communities responded with increased richness and decreased diversity when exposed to petroleum contamination. The dominant class changed from Deltaproteobacteria to Gammaproteobacteria after petroleum contamination. The phylum Firmicutes increased dramatically in oil-enriched sediment by 75.78%, 346.19% and 267.26% in LP, HP and TD, respectively. One of the suspected oil-degrading genera, Dechloromonas, increased the most in oil-contaminated sediment, by 540.54%, 711.27% and 656.78% in LP, HP and TD, respectively. Spore protease, quinate dehydrogenase (quinone) and glutathione-independent formaldehyde dehydrogenase, three types of identified enzymes, increased enormously with the increasing petroleum concentration. In conclusion, petroleum contamination altered the community composition and microorganism structure, and promoted some bacteria to produce the corresponding degrading enzymes. Additionally, the suspected petroleum-degrading genera should be considered when restoring oil-contaminated sediment.

Microbial community successional patterns in offshore sediments impacted by chemical pollution from Taizhou and Xiamen Cities in China

An Illumina-based next-generation sequencing was employed to characterise the sediment microbiome adjacent to coastal industrial and tourist cities, Taizhou and Xiamen, in China, and their associations with chemical pollution were explored. The results indicated that chemical pollution of sediments from Taizhou was higher than that from Xiamen. The number of sediment bacterial genera was negatively (Taizhou) or positively (Xiamen) correlated with offshore distance, owing to shifts in the primary and secondary status of organic matter and chemical pollutants for the promotion or inhibition of the sediment microbiome. The total number of the operational taxonomic units (OTUs) in sediments from Taizhou was larger than from Xiamen, while the number of core OTUs was smaller indicating that Taizhou had more impact on core microbes in sediments than Xiamen. This study suggests that chemical pollutants and organic matter result in different co-regulation of the off-shore sediment microbiome of coastal industrial and tourist cities.

Indigenous PAH degraders along the gradient of the Yangtze Estuary of China: Relationships with pollutants and their bioremediation implications

This study investigated the network of polycyclic aromatic hydrocarbon (PAH) degraders in the Yangtze estuarine and coastal areas. Along the estuarine gradients, Proteobacteria and Bacteroidetes were the dominant bacterial phyla, and forty-six potential PAH degraders were identified. The abundance of genes encoding the alpha subunit of the PAH-ring hydroxylating dioxygenases (PAH-RHDα) of gram-negative bacteria ranged from 5.5 × 10⁵ to 5.8 × 10⁷ copies g^-1, while that of gram-positive bacteria ranged from 1.3 × 10⁵ to 2.0 × 10⁷ copies g^-1. The PAH-degraders could represent up to 0.2% of the total bacterial community and mainly respond to PAHs and Cu concentrations, which indicate anthropogenic activities. Salinity and pH showed negative regulating effects on the PAH-degrading potential and the tolerance of bacteria to pollutants. PAH degraders such as Novosphingobium and Mycobacterium exhibit heavy-metal tolerance and core roles in the network of PAH degraders. These outcomes have important implications for bioremediation.

Effects of ofloxacin on nitrogen removal and microbial community structure in constructed wetland

Constructed wetlands (CWs) have emerged as a promising technology for the purification of micro-polluted water. However, their nitrogen removal performance can be significantly degraded by design, operational, and environmental factors. The present study investigates the effects of ofloxacin (OFL: 0.1, 10, and 1000 μg L^-1) and plants (Cyperus alternifolius L. and Typha angustifolia L.) on nitrogen removal in a micro-polluted CW system over a duration of 12 weeks. The effects were evaluated by investigating NH₄-N and NO₃-N removal efficiency, nitrification genes (amoA-AOA and amoA-AOB), denitrification genes (nirK and nirS), fungal 18S rRNA gene and microorganism community structure. The results showed that in unplanted CWs, OFL increased the NH₄-N removal efficiency (from 72.6% to 80.7-82.1%), the abundances of amoA-AOA, nirS, nirK and fungal 18S rRNA gene, and the bacterial diversity but decreased the abundance of both amoA-AOB and bacterial richness. In contrast, both the nitrogen removal efficiency (83.4-89.5% for NH₄-N and 33.8-38.5% for NO₃-N) and bacterial diversity/richness were not significantly affected by OFL in planted CWs. In planted systems, OFL increased the relative abundance of Arthrobacter, Pseudomonas, and Enterococcus, which are proven antibiotic-resistant bacteria. This study showed that CWs are able to remove nitrogen from antibiotic-contaminated micro-polluted water, which might primarily be attributed to the presence of plants that protect the microorganism community.

Biodegradation of enrofloxacin by microbial consortia obtained from rhizosediments of two estuarine plants

This study aimed to investigate the potential of microbial communities from the rhizosediment of two plants - Phragmites australis and Juncus maritimus - occurring in an estuarine area subjected to a high anthropogenic impact, to biodegrade ENR, a commonly used veterinary antibiotic. An enrichment process with 1 mgL^-1 of ENR was conducted during ca. 9 months, using acetate as a co-substrate. After this, the enriched microbial consortia were challenged with higher ENR concentrations of 2 and 3 mgL^-1. Microbial cultures enriched with 1 mgL^-1 of ENR were capable of biodegrading this antibiotic, though not completely. By the end of the enrichment phase, microbial cultures were defluorinating an average of 50% of the ENR supplemented. Higher ENR concentrations led to lower biodegradation performances, suggesting a possible toxic/inhibitory effect in the microbial cultures. Phylogenetic identification of the microorganisms isolated from microbial cultures enriched with ENR revealed a high taxonomical diversity, with microorganisms belonging mainly to Proteobacteria and Bacteroidetes phyla. Assemblage of the obtained isolated strains (according to the enriched cultures from which they were isolated) revealed that the resulting consortia were also capable of degrading ENR, indicating that the main microbial players in the biodegradation of this antibiotic were isolated. These consortia also showed to be more robust to degrade higher concentrations of ENR than the corresponding enriched cultures. This study shows that microorganisms derived from rhizosediments of the selected plants, exhibit capacity to biodegrade ENR, though not completely for the concentrations tested, and may be further explored for the development of bioremediation strategies for the treatment of this antibiotic.

Removal of chlorpyrifos in recirculating vertical flow constructed wetlands with five wetland plant species

The removal efficiency of the pesticide chlorpyrifos (50 and 500 μg L^-1) by five wetland plant species (Cyperus alternifolius, Canna indica, Iris pseudacorus, Juncus effusus and Typha orientalis) was studied in recirculating vertical flow constructed wetland systems (RVFCWs). Results reveal that for chlorpyrifos at different concentrations, good removal efficiencies (94-98%) were observed using the same plant systems, while no significant differences in removal efficiencies were seen between the different plant systems. In addition, the chlorpyrifos removal efficiency of the planted systems increased significantly compared with the unplanted controls. The chlorpyrifos removal efficiency for wetland systems over time fit to the first-order kinetic model, with the first-order kinetic constant (k) ranging from 0.045 to 0.065 h^-1. The half-life of chlorpyrifos in the systems ranged from 10.66-15.43 h. The shortest chlorpyrifos half-life was detected in the wetland system containing C. indica, followed by that with C. alternifolius and I. pseudacorus. The main pathways to remove chlorpyrifos in these wetland systems were sorption (accounting for 64.6-86.4% of the total removal efficiency) and biodegradation (8.1-33.7%). Plants can enhance chlorpyrifos removal through enhanced biodegradation in the system. Plants with high biomass and transpiration were able to accelerate the removal of chlorpyrifos and conventional pollutants. Hence, C. indica, C. alternifolius and I. pseudacorus could be used as optimal plants for pesticide removal in wetland systems.

Occurrence, sources and health risk of polycyclic aromatic hydrocarbons in soils around oil wells in the border regions between oil fields and suburbs

The Yellow River Delta (YRD) is a typical region where oil fields generally overlap cities and towns, leading to complex soil contamination from both the oil fields and human activities. To clarify the distribution, speciation, potential sources and health risk of polycyclic aromatic hydrocarbons (PAHs) in soils of border regions between oil fields and suburbs of the YRD, 138 soil samples (0-20 cm) were collected among 12 sampling sites located around oil wells with different extraction histories. The 16 priority control PAHs (16PAHs), as selected by the United States Environmental Protection Agency (USEPA), were extracted via an accelerated solvent extraction and detected by GC-MS. The results showed that soils of the study area were generally polluted by the 16PAHs. Among these pollutions, chrysene and phenanthrene were the dominant components, and 4-ring PAHs were the most abundant. A typical temporal distribution pattern of the 16PAHs was revealed in soils from different sampling sites around oil wells with different exploitation histories. The concentrations of total 16PAHs and high-ring PAHs (HPAHs) both increased with the extraction time of the nearby oil wells. Individual PAH ratios and PCA method revealed that the 16PAHs in soil with newly developed oil wells were mainly from petroleum pollutants, whereas PAHs in soils around oil wells with a long exploitation history were probably from petroleum contamination; combustion of petroleum, fuel, and biomass; and degradation and migration of PAHs from petroleum. Monte Carlo simulation was used to evaluate the health risks of the 7 carcinogenic PAHs and 9 non-carcinogenic PAHs in the study area. The results indicated that ingestion and dermal contact were the predominant pathways of exposure to PAH residues in soils. Both the carcinogenic and non-carcinogenic burden of the 16PAHs in soils of the oil field increased significantly with exploitation time of nearby oil wells.

Performance evaluation of duplex constructed wetlands for the treatment of diesel contaminated wastewater

A duplex constructed wetland (duplex-CW) is a hybrid system that combines a vertical flow (VF) CW as a first stage with a horizontal flow filter (HFF) as a second stage for a more efficient wastewater treatment as compared to traditional constructed wetlands. This study evaluated the potential of the hybrid CW system to treat influent wastewater containing diesel range organic compounds varying from C₇ - C₄₀ using a series of 12-week practical and numerical experiments under controlled conditions in a greenhouse (pH was kept at 7.0 ± 0.2, temperature between 20 and 23° C and light intensity between 85 and 100-μmol photons m^-2 sec^-1 for 16 h d^-1). The VF CWs were planted with Phragmites australis and were spiked with different concentrations of NH₄⁺-N (10, 30 and 60 mg/L) and PO₄^3--P (3, 6 and 12 mg/L) to analyse their effects on the degradation of the supplied petroleum hydrocarbons. The removal rate of the diesel range organics considering the different NH₄⁺-N and PO₄^3--P concentrations were simulated using Monod degradation kinetics. The simulated results compared well with the observed database. The results showed that the model can effectively be used to predict biochemical transformation and degradation of diesel range organic compounds along with nutrient amendment in duplex constructed wetlands.

Potential of dissimilatory nitrate reduction pathways in polycyclic aromatic hydrocarbon degradation

This study investigates the potential of an indigenous estuarine microbial consortium to degrade two polycyclic aromatic hydrocarbons (PAHs), naphthalene and fluoranthene, under nitrate-reducing conditions. Two physicochemically diverse sediment samples from the Lima Estuary (Portugal) were spiked individually with 25 mg L^-1 of each PAH in laboratory designed microcosms. Sediments without PAHs and autoclaved sediments spiked with PAHs were run in parallel. Destructive sampling at the beginning and after 3, 6, 12, 30 and 63 weeks incubation was performed. Naphthalene and fluoranthene levels decreased over time with distinct degradation dynamics varying with sediment type. Next-generation sequencing (NGS) of 16 S rRNA gene amplicons revealed that the sediment type and incubation time were the main drivers influencing the microbial community structure rather than the impact of PAH amendments. Predicted microbial functional analyses revealed clear shifts and interrelationships between genes involved in anaerobic and aerobic degradation of PAHs and in the dissimilatory nitrate-reducing pathways (denitrification and dissimilatory nitrate reduction to ammonium - DNRA). These findings reinforced by clear biogeochemical denitrification signals (NO₃^- consumption, and NH₄⁺ increased during the incubation period), suggest that naphthalene and fluoranthene degradation may be coupled with denitrification and DNRA metabolism. The results of this study contribute to the understanding of the dissimilatory nitrate-reducing pathways and help uncover their involvement in degradation of PAHs, which will be crucial for directing remediation strategies of PAH-contaminated anoxic sediments.

Bacterial community dynamic associated with autochthonous bioaugmentation for enhanced Cu phytoremediation of salt-marsh sediments

Autochthonous bioaugmentation for metal phytoremediation is still little explored, particularly its application to estuarine salt marshes, but results obtained so far are promising. Nevertheless, understanding the behaviour of the microbial communities in the process of bioaugmentation and their role in improving metal phytoremediation is very important to fully validate the application of this biological technology. This study aimed to characterize the bacterial community dynamic associated with the application of autochthonous bioaugmentation in an experimentation which showed that Phragmites australis rhizosphere microorganisms could increase this salt marsh plant potential to phytoremediate Cu contaminated sediments. Bacterial communities present in the autochthonous microbial consortium resistant to Cu added to the medium and in the sediment at the beginning and at the end of the experiment were characterized by ARISA. Complementarily, the consortium and the sediment used for its production were characterized by next generation sequencing using the pyrosequencing platform 454. The microbial consortium resistant to Cu obtained from non-vegetated sediment was dominated by the genus Lactococcus (46%), Raoultella (25%), Bacillus (12%) and Acinetobacter (11%), whereas the one obtained form rhizosediment was dominated by the genus Gluconacetobacter (77%), Bacillus (17%) and Dyella (3%). Results clearly showed that, after two months of experiment, Cu caused a shift in the bacterial community structure of sediments, an effect that was observed either with or without addition of the metal resistant microbial consortium. Therefore, bioaugmentation application improved the process of phytoremediation (metal translocation by the plant was increased) without inducing long term changes in the bacterial community structure of the sediments. So, phytoremediation combined with autochthonous bioaugmentation can be a suitable technology for the recovery of estuarine areas, contributing for an efficient risk management strategy of these coastal zones.

Biosurfactant-producing microorganism Pseudomonas sp. SB assists the phytoremediation of DDT-contaminated soil by two grass species

Phytoremediation together with microorganisms may confer the advantages of both phytoremediation and microbial remediation of soils containing organic contaminants. In this system biosurfactants produced by Pseudomonas sp. SB may effectively help to increase the bioavailability of organic pollutants and thereby enhance their microbial degradation in soil. Plants may enhance the rhizosphere environment for microorganisms and thus promote the bioremediation of contaminants. In the present pot experiment study, dichlorodiphenyltrichloroethane (DDT) residues underwent an apparent decline after soil bioremediation compared with the original soil. The removal efficiency of fertilizer + tall fescue, fertilizer + tall fescue + Pseudomonas, fertilizer + perennial ryegrass, and fertilizer + perennial ryegrass + Pseudomonas treatments were 59.4, 65.6, 69.0, and 65.9%, respectively, and were generally higher than that in the fertilizer control (40.3%). Principal coordinates analysis (PCoA) verifies that plant species greatly affected the soil bacterial community irrespective of inoculation with Pseudomonas sp. SB. Furthermore, community composition analysis shows that Proteobacteria, Acidobacteria and Actinobacteria were the three dominant phyla in all groups. In particular, the relative abundance of Pseudomonas for fertilizer + tall fescue + Pseudomonas (0.25%) was significantly greater than fertilizer + tall fescue and this was related to the DDT removal efficiency.

Evaluation of laboratory-scale in situ capping sediments with purple parent rock to control the eutrophication

In this study, the effectiveness of controlling the eutrophication using purple parent rock to cap the sediments was evaluated in the laboratory scale. Sediments were collected from Sanxikou reservoir (China) in July 2013. Then, three types of purple parent rock (T₁f, J₃p, and J₂s) which are distributed widely in southwest China were used to cap the sediments. Limestone and calcite were used as the contrast group, because they had been reported as effective controls on eutrophication. Then, they were incubated at 20 °C for 46 days. The results indicated that the application of purple parent rock as a barrier material can effectively inhibit the release of nutrient elements in sediments, and the inhibition rates of total nitrogen (TN), total phosphorus (TP), ammonium (NH₄-N), and nitrate (NO₃-N) were much better than that of limestone and calcite. Among the three types of purple parent rock, J₃p exhibited the best inhibitory effect on the release of nitrogen in sediments, and the inhibition efficiency of TN, NH₄-N, and NO₃-N was 59.7, 77.6, and 45.1%, respectively. As for T₁f, it exhibited the best inhibitory effect on the release of TP in sediments with the inhibition rate of 94.4%. Whereas all these capping materials showed weak inhibition on release of organic matter in sediments, and the inhibition efficiencies were less than 20%. Moreover, these treatments could also cause distinct changes in the microbial community in sediments and overlying water, and the contents of TN and TP in all capping materials increased. All results demonstrated that purple parent rock could inhibit the release of nutrient in sediments through mechanical interception, physical adsorption, and chemical absorption as well as changing the microbial activity in the covering layer, sediments, or overlying water.

Juncus spp.-The helophyte for all (phyto)remediation purposes?

Helophytic plants contribute significantly to the remediation of ecosystems through a wide range of physiological or biochemical mechanisms including the role of endophytic bacteria. This review highlights the services provided by Juncus spp. wetland plants, from phytoremediation of soils and groundwater with heavy metals and/or organics to municipal or industrial wastewater treatment in constructed wetlands. The data presented also provide information on the efficiency of specific Juncus spp. in response to various metals and organic compounds, in an effort to exploit the natural capabilities of autochthonous over exotic species in phytoremediation strategies. An overall successful direct (the plant itself) or indirect (through stimulation of elimination mechanisms) contribution of Juncus to remediation of the above contaminants is revealed. However, the specific characteristics of the species used, the type of the pollutant and the region, are issues that should be addressed for a successful outcome.

Temporal dynamics of sediment bacterial communities in monospecific stands of Juncus maritimus and Spartina maritima

In the present study, we used 16S rRNA barcoded pyrosequencing to investigate to what extent monospecific stands of different salt marsh plant species (Juncus maritimus and Spartina maritima), sampling site and temporal variation affect sediment bacterial communities. We also used a bioinformatics tool, PICRUSt, to predict metagenome gene functional content. Our results showed that bacterial community composition from monospecific stands of both plant species varied temporally, but both host plant species maintained compositionally distinct communities of bacteria. Juncus sediment was characterised by higher abundances of Alphaproteobacteria, Myxococcales, Rhodospirillales, NB1-j and Ignavibacteriales, while Spartina sediment was characterised by higher abundances of Anaerolineae, Synechococcophycidae, Desulfobacterales, SHA-20 and Rhodobacterales. The differences in composition and higher taxon abundance between the sediment bacterial communities of stands of both plant species may be expected to affect overall metabolic diversity. In line with this expectation, there were also differences in the predicted enrichment of selected metabolic pathways. In particular, bacterial communities of Juncus sediment were predicted to be enriched for pathways related to the degradation of various (xenobiotic) compounds. Bacterial communities of Spartina sediment in turn were predicted to be enriched for pathways related to the biosynthesis of various bioactive compounds. Our study highlights the differences in composition and predicted functions of sediment-associated bacterial communities from two different salt marsh plant species. Loss of salt marsh habitat may thus be expected to both adversely affect microbial diversity and ecosystem functioning and have consequences for environmental processes such as nutrient cycling and pollutant remediation.

Differential effects of crude oil on denitrification and anammox, and the impact on N2O production

Denitrification and anammox are key processes for reducing the external nitrogen loads delivered to coastal ecosystems, and these processes can be affected by pollutants. In this study, we investigated the effect of crude oil on denitrification and anammox. Controlled laboratory experiments were performed using sediment slurries from the Lima Estuary (NW Portugal). Anammox and denitrification rates were measured using (15)N-labeled NO3(-), and the production of (29)N2 and (30)N2 quantified by membrane inlet mass spectrometry. Results revealed that while denitrification rates were stimulated between 10 and 25 000 times after crude oil amendment, anammox activity was partially (between 2 and 5 times) or completely inhibited by the addition of crude oil when comparing to rates in unamended controls. Similar results were observed across four estuarine sediment types, despite their different physical-chemical characteristics. Moreover, N2O production was reduced by 2-36 times following crude oil addition. Further work is required to fully understand the mechanism(s) of the observed reduction in N2O production. This study represents one of the first contributions to the understanding of the impact of crude oil pollution on denitrification and anammox, with profound implications for the management of aquatic ecosystems regarding eutrophication (N-removal).

Bacterial community analysis of an industrial wastewater treatment plant in Colombia with screening for lipid-degrading microorganisms

The operation of wastewater treatment technologies depends on a combination of physical, chemical and biological factors. Microorganisms present in wastewater treatment plants play essential roles in the degradation and removal of organic waste and xenobiotic pollutants. Several microorganisms have been used in complementary treatments to process effluents rich in fats and oils. Microbial lipases have received significant industrial attention because of their stability, broad substrate specificity, high yields, and regular supply, as well as the fact that the microorganisms producing them grow rapidly on inexpensive media. In Colombia, bacterial community studies have focused on populations of cultivable nitrifying, heterotrophic and nitrogen-fixing bacteria present in constructed wetlands. In this study, culture-dependent methods, culture-independent methods (TTGE, RISA) and enzymatic methods were used to estimate bacterial diversity, to monitor temporal and spatial changes in bacterial communities, and to screen microorganisms that presented lipolytic activity. The dominant microorganisms in the Wastewater Treatment Plant (WWTP) examined in this study belonged to the phyla Firmicutes, Proteobacteria and Bacteroidetes. The enzymatic studies performed indicated that five bacterial isolates and three fungal isolates possessed the ability to degrade lipids; additionally, the Serratia, Kosakonia and Mucor genera presented lipase-mediated transesterification activity. The implications of these findings in regard to possible applications are discussed later in this paper. Our results indicate that there is a wide diversity of aerobic Gram-negative bacteria inhabiting the different sections of the WWTP, which could indicate its ecological condition, functioning and general efficiency.

Occurrence of persistent organic pollutants in sediments and biota from Portugal versus European incidence: A critical overview

Persistent organic pollutants (POPs) are widespread compounds, such as organohalogenated compounds, polycyclic aromatic hydrocarbons (PAHs) and pesticides, which can be found in all types of environmental compartments. Their presence in the aquatic environment is a worldwide problem, with emphasis on sediments which act as depository and consequently as a source of hydrophobic, recalcitrant and harmful compounds. Besides, these pollutants might affect the reproduction and mortality of living organisms, diverging in their potential to bioaccumulate in tissues. The present paper aims to review the occurrence of POPs in sediments and biota from the coastal, estuarine and river areas of Portugal. The list of the studied compounds comprises organohalogenated compounds, PAHs, organometallic compounds, pesticides, sterols, fatty acids and pharmaceutical compounds. The contamination of sediments by various pollutants is presented, such as PAHs up to 7,350 ng g(-1) found in Sado estuary and polychlorinated biphenyls up to 62.2 ng g(-1) in the case of sediments collected in Ria de Aveiro. The occurrence of these persistent toxic substances in sediments demonstrates aquatic contamination from agricultural, industrial and urban discharges and the concern about the potential risks to aquatic organisms, wildlife and humans. In fact, several classes of POPs have also been found in biota, such as polychlorinated biphenyls up to 810.9 ng g(-1) in sentinel fish from the Douro River estuary and pesticides in bivalves from the Sado River estuary. The importance of further systematic research on sediments and biota is here highlighted to compare the contamination of these two reservoirs; to assess their spatial and temporal variation; and to determine other classes of POPs that were not investigated yet (e.g., industrial compounds, estrogens and many classes of pharmaceuticals).

Bacterial diversity is strongly associated with historical penguin activity in an Antarctic lake sediment profile

Current penguin activity in Antarctica affects the geochemistry of sediments and their microbial communities; the effects of historical penguin activity are less well understood. Here, bacterial diversity in ornithogenic sediment was investigated using high-throughput pyrosequencing. The relative abundances of dominant phyla were controlled by the amount of historical penguin guano deposition. Significant positive correlations were found between both the bacterial richness and diversity, and the relative penguin number (p < 0.01); this indicated that historical penguin activity drove the vertical distribution of the bacterial communities. The lowest relative abundances of individual phyla corresponded to lowest number of penguin population at 1,800–2,300 yr BP during a drier and colder period; the opposite was observed during a moister and warmer climate (1,400–1,800 yr BP). This study shows that changes in the climate over millennia affected penguin populations and the outcomes of these changes affect the sediment bacterial community today.

Response of a salt marsh microbial community to antibiotic contamination

Salt marsh plants and associated microorganisms can have an important role in contaminant removal from estuaries, through bioremediation processes. Nevertheless, the interaction between emerging contaminants, namely antibiotics, and plant-microorganism associations in estuarine environment are still scarcely known. In this vein, the aim of the present study was to evaluate, in controlled conditions, the response of a salt marsh plant-microorganism association to a contamination with a veterinary antibiotic. For that a salt marsh plant (Phragmites australis) and its respective rhizosediment were collected in a temperate estuary (Lima estuary, NW Portugal) and exposed for 7 days to enrofloxacin (ENR) under different nutritional conditions in sediment elutriates. Response was evaluated in terms of ENR removal and changes in microbial community structure (evaluated by ARISA) and abundance (estimated by DAPI). In general, no significant changes were observed in microbial abundance. Changes in bacterial richness and diversity were observed but only in unplanted systems. However, multivariate analysis of ARISA profiles showed significant effect of both the presence of plant and type of treatment on the microbial community structure, with significant differences among all treatment groups. In addition, plants and associated microorganisms presented a potential for antibiotic removal that, although highly dependent on their nutritional status, can be a valuable asset to recover impacted areas such as estuarine ones.

Long-term oil contamination causes similar changes in microbial communities of two distinct soils

Since total petroleum hydrocarbons (TPH) are toxic and persistent in environments, studying the impact of oil contamination on microbial communities in different soils is vital to oil production engineering, effective soil management and pollution control. This study analyzed the impact of oil contamination on the structure, activity and function in carbon metabolism of microbial communities of Chernozem soil from Daqing oil field and Cinnamon soil from Huabei oil field through both culture-dependent techniques and a culture-independent technique-pyrosequencing. Results revealed that pristine microbial communities in these two soils presented disparate patterns, where Cinnamon soil showed higher abundance of alkane, (polycyclic aromatic hydrocarbons) PAHs and TPH degraders, number of cultivable microbes, bacterial richness, bacterial biodiversity, and stronger microbial activity and function in carbon metabolism than Chernozem soil. It suggested that complicated properties of microbes and soils resulted in the difference in soil microbial patterns. However, the changes of microbial communities caused by oil contamination were similar in respect of two dominant phenomena. Firstly, the microbial community structures were greatly changed, with higher abundance, higher bacterial biodiversity, occurrence of Candidate_division_BRC1 and TAO6, disappearance of BD1-5 and Candidate_division_OD1, dominance of Streptomyces, higher percentage of hydrocarbon-degrading groups, and lower percentage of nitrogen-transforming groups. Secondly, microbial activity and function in carbon metabolism were significantly enhanced. Based on the characteristics of microbial communities in the two soils, appropriate strategy for in situ bioremediation was provided for each oil field. This research underscored the usefulness of combination of culture-dependent techniques and next-generation sequencing techniques both to unravel the microbial patterns and understand the ecological impact of contamination.

Influence of Land Use, Nutrients, and Geography on Microbial Communities and Fecal Indicator Abundance at Lake Michigan Beaches

Microbial communities within beach sand play a key role in nutrient cycling and are important to the nearshore ecosystem function. Escherichia coli and enterococci, two common indicators of fecal pollution, have been shown to persist in the beach sand, but little is known about how microbial community assemblages are related to these fecal indicator bacteria (FIB) reservoirs. We examined eight beaches across a geographic gradient and range of land use types and characterized the indigenous community structure in the water and the backshore, berm, and submerged sands. FIB were found at similar levels in sand at beaches adjacent to urban, forested, and agricultural land and in both the berm and backshore. However, there were striking differences in the berm and backshore microbial communities, even within the same beach, reflecting the very different environmental conditions in these beach zones in which FIB can survive. In contrast, the microbial communities in a particular beach zone were similar among beaches, including at beaches on opposite shores of Lake Michigan. The differences in the microbial communities that did exist within a beach zone correlated to nutrient levels, which varied among geographic locations. Total organic carbon and total phosphorus were higher in Wisconsin beach sand than in beach sand from Michigan. Within predominate genera, fine-scale sequence differences could be found that distinguished the populations from the two states, suggesting a biogeographic effect. This work demonstrates that microbial communities are reflective of environmental conditions at freshwater beaches and are able to provide useful information regarding long-term anthropogenic stress.

Microbial community dynamics associated with veterinary antibiotics removal in constructed wetlands microcosms

This study aimed to evaluate the response of the microbial community from CWs microcosms tested for the removal of two veterinary antibiotics, enrofloxacin (ENR) and tetracycline (TET), from livestock industry wastewater. Three treatments were tested (control, ENR or TET (100 μg L(-1))) over 12 weeks in microcosms unplanted and planted with Phragmites australis. CWs removal efficiency was relatively stable along time, with removals higher than 98% for ENR and 94% for TET. In addition, CWs were able to reduce wastewater toxicity, independently of antibiotics presence. Despite no significant differences were observed in terms of microbial abundance, bacterial richness or diversity, analysis of similarities (two-way crossed ANOSIM) showed a significant effect of both time and treatments in bacterial community structure. This study points to CWs applicability for veterinary antibiotics removal from livestock wastewaters, showing that CWs microbial communities were able to adapt without significant changes in their diversity or depuration capacity.

Initial community and environment determine the response of bacterial communities to dispersant and oil contamination

Bioremediation of seawater by natural bacterial communities is one potential response to coastal oil spills, but the success of the approach may vary, depending on geographical location, oil composition and the timing of spill. The short term response of coastal bacteria to dispersant, oil and dispersed oil was characterized using 16S rRNA gene tags in two mesocosm experiments conducted two months apart. Despite differences in the amount of oil-derived alkanes across the treatments and experiments, increases in the contributions of hydrocarbon degrading taxa and decreases in common estuarine bacteria were observed in response to dispersant and/or oil. Between the two experiments, the direction and rates of changes in particulate alkane concentrations differed, as did the magnitude of the bacterial response to oil and/or dispersant. Together, our data underscore large variability in bacterial responses to hydrocarbon pollutants, implying that bioremediation success varies with starting biological and environmental conditions.

Salt marsh sediment characteristics as key regulators on the efficiency of hydrocarbons bioremediation by Juncus maritimus rhizospheric bacterial community

Mitigation of petroleum hydrocarbons was investigated during a 5-month greenhouse experiment, to assess the rhizoremediation (RR) potential in sediments with different characteristics colonized by Juncus maritimus, a salt marsh plant commonly found in temperate estuaries. Furthermore, the efficiency of two bioremediation treatments namely biostimulation (BS) by the addition of nutrients, and bioaugmentation (BA) by addition of indigenous microorganisms, was tested in combination with RR. The effect of the distinct treatments on hydrocarbon degradation, root biomass weight, and bacterial community structure was assessed. Our result showed higher potential for hydrocarbon degradation (evaluated by total petroleum hydrocarbon analysis) in coarse rhizosediments with low organic matter (OM), than rhizosediments with high OM, and small size particles. Moreover, the bacterial community structure was shaped according to the rhizosediment characteristics, highlighting the importance of specific microbe-particle associations to define the structure of rhizospheric bacterial communities, rather than external factors, such as hydrocarbon contamination or the applied treatments. The potential for hydrocarbon RR seems to depend on root system development and bacterial diversity, since biodegradation efficiencies were positively related with these two parameters. Treatments with higher root biomass, and concomitantly with higher bacterial diversity yielded higher hydrocarbon degradation. Moreover, BS and BA did not enhance hydrocarbons RR. In fact, it was observed that higher nutrient availability might interfere with root growth and negatively influence hydrocarbon degradation performance. Therefore, our results suggested that to conduct appropriate hydrocarbon bioremediation strategies, the effect of sediment characteristics on root growth/exploration should be taken into consideration, a feature not explored in previous studies. Furthermore, strategies aiming for the recovery of bacterial diversity after oil spills may improve the efficiency of hydrocarbon biodegradation in contaminated salt marsh sediments.

Diversity of bacterial communities along a petroleum contamination gradient in desert soils

Microbial communities in oil-polluted desert soils have been rarely studied compared to their counterparts from freshwater and marine environments. We investigated bacterial diversity and changes therein in five desert soils exposed to different levels of oil pollution. Automated rRNA intergenic spacer (ARISA) analysis profiles showed that the bacterial communities of the five soils were profoundly different (analysis of similarities (ANOSIM), R = 0.45, P < 0.0001) and shared less than 20 % of their operational taxonomic units (OTUs). OTU richness was relatively higher in the soils with the higher oil pollution levels. Multivariate analyses of ARISA profiles revealed that the microbial communities in the S soil, which contains the highest level of contamination, were different from the other soils and formed a completely separate cluster. A total of 16,657 ribosomal sequences were obtained, with 42-89 % of these sequences belonging to the phylum Proteobacteria. While sequences belonging to Betaproteobacteria, Gammaproteobacteria, Bacilli, and Actinobacteria were encountered in all soils, sequences belonging to anaerobic bacteria from the classes Deltaproteobacteria, Clostridia, and Anaerolineae were only detected in the S soil. Sequences belonging to the genus Terriglobus of the class Acidobacteria were only detected in the B3 soil with the lowest level of contamination. Redundancy analysis (RDA) showed that oil contamination level was the most determinant factor that explained variations in the microbial communities. We conclude that the exposure to different levels of oil contamination exerts a strong selective pressure on bacterial communities and that desert soils are rich in aerobic and anaerobic bacteria that could potentially contribute to the degradation of hydrocarbons.

Copper phytoremediation by a salt marsh plant (Phragmites australis) enhanced by autochthonous bioaugmentation

Here we evaluated whether the potential of Phragmites australis to phytoremediate Cu contaminated sediments could be enhanced by bioaugmentation with an autochthonous microorganism consortium (AMC) that is resistant to Cu. Saltmarsh plants with sediment attached to their roots were collected, placed in vessels and kept in greenhouses, under tidal simulation. Sediments were contaminated with Cu and the AMC was added to half of the vessels. After two months, plants accumulated significant amounts of Cu (2-10 times more) in all tissues although in higher amounts (7-10 times more) in belowground structures. AMC addition increased Cu bioavailability (5-10%) in sediments leading to a decrease in belowground structures biomass. However, bioaugmentation increased Cu translocation, with higher amounts (2 times more) of Cu in the plant stems, without significant visual toxicity signs. Therefore, autochthonous bioaugmentation can increase Cu phytoextraction potential of P. australis, which can be a valuable strategy for the recovery and management of moderately impacted estuaries.

Abundance and diversity of soil petroleum hydrocarbon-degrading microbial communities in oil exploring areas

Alkanes and polycyclic aromatic hydrocarbons (PAHs) are the commonly detected petroleum hydrocarbon contaminants in soils in oil exploring areas. Hydrocarbon-degrading genes are useful biomarks for estimation of the bioremediation potential of contaminated sites. However, the links between environmental factors and the distribution of alkane and PAH metabolic genes still remain largely unclear. The present study investigated the abundances and diversities of soil n-alkane and PAH-degrading bacterial communities targeting both alkB and nah genes in two oil exploring areas at different geographic regions. A large variation in the abundances and diversities of alkB and nah genes occurred in the studied soil samples. Various environmental variables regulated the spatial distribution of soil alkane and PAH metabolic genes, dependent on geographic location. The soil alkane-degrading bacterial communities in oil exploring areas mainly consisted of Pedobacter, Mycobacterium, and unknown alkB-harboring microorganisms. Moreover, the novel PAH-degraders predominated in nah gene clone libraries from soils of the two oil exploring areas. This work could provide some new insights towards the distribution of hydrocarbon-degrading microorganisms and their biodegradation potential in soil ecosystems.

Development of autochthonous microbial consortia for enhanced phytoremediation of salt-marsh sediments contaminated with cadmium

Microbial assisted phytoremediation is a promising, though yet poorly explored, new remediation technique. The aim of this study was to develop autochthonous microbial consortia resistant to cadmium that could enhance phytoremediation of salt-marsh sediments contaminated with this metal. The microbial consortia were selectively enriched from rhizosediments colonized by Juncus maritimus and Phragmites australis. The obtained consortia presented similar microbial abundance but a fairly different community structure, showing that the microbial community was a function of the sediment from which the consortia were enriched. The effect of the bioaugmentation with the developed consortia on cadmium uptake, and the microbial community structure associated to the different sediments were assessed using a microcosm experiment. Our results showed that the addition of the cadmium resistant microbial consortia increased J. maritimus metal phytostabilization capacity. On the other hand, in P. australis, microbial consortia amendment promoted metal phytoextraction. The addition of the consortia did not alter the bacterial structure present in the sediments at the end of the experiments. This study provides new evidences that the development of autochthonous microbial consortia for enhanced phytoremediation of salt-marsh sediments contaminated with cadmium might be a simple, efficient, and environmental friendly remediation procedure.

CAPSULE ABSTRACT

Development of autochthonous microbial consortia resistant to cadmium that enhanced phytoremediation by salt-marsh plants, without a long term effect on sediment bacterial diversity.

Phytomediated biostimulation of the autochthonous bacterial community for the acceleration of the depletion of polycyclic aromatic hydrocarbons in contaminated sediments

Polycyclic aromatic hydrocarbons (PAHs) are a large group of organic contaminants causing hazards to organisms including humans. The objective of the study was to validate the vegetation of dredged sediments with Phragmites australis as an exploitable biostimulation approach to accelerate the depletion of PAHs in nitrogen spiked sediments. Vegetation with Phragmites australis resulted in being an efficient biostimulation approach for the depletion of an aged PAHs contamination (229.67 ± 15.56 μg PAHs/g dry weight of sediment) in dredged sediments. Phragmites australis accelerated the oxidation of the PAHs by rhizodegradation. The phytobased approach resulted in 58.47% of PAHs depletion. The effects of the treatment have been analyzed in terms of both contaminant depletion and changes in relative abundance of the metabolically active Gram positive and Gram negative PAHs degraders. The metabolically active degraders were quantified both in the sediments and in the root endospheric microbial community. Quantitative real-time PCR reactions have been performed on the retrotranscribed transcripts encoding the Gram positive and Gram negative large α subunit (RHDα) of the aromatic ring hydroxylating dioxygenases. The Gram positive degraders resulted in being selectively favored by vegetation with Phragmites australis and mandatory for the depletion of the six ring condensed indeno[1,2,3-cd]pyrene and benzo[g,h,i]perylene.