Impact of pyrene and cadmium co-contamination on prokaryotic community in coastal sediment microcosms

Where the rubber meets the road: Emerging environmental impacts of tire wear particles and their chemical cocktails

About 3 billion new tires are produced each year and about 800 million tires become waste annually. Global dependence upon tires produced from natural rubber and petroleum-based compounds represents a persistent and complex environmental problem with only partial and often-times, ineffective solutions. Tire emissions may be in the form of whole tires, tire particles, and chemical compounds, each of which is transported through various atmospheric, terrestrial, and aquatic routes in the natural and built environments. Production and use of tires generates multiple heavy metals, plastics, PAH's, and other compounds that can be toxic alone or as chemical cocktails. Used tires require storage space, are energy intensive to recycle, and generally have few post-wear uses that are not also potential sources of pollutants (e.g., crumb rubber, pavements, burning). Tire particles emitted during use are a major component of microplastics in urban runoff and a source of unique and highly potent toxic substances. Thus, tires represent a ubiquitous and complex pollutant that requires a comprehensive examination to develop effective management and remediation. We approach the issue of tire pollution holistically by examining the life cycle of tires across production, emissions, recycling, and disposal. In this paper, we synthesize recent research and data about the environmental and human health risks associated with the production, use, and disposal of tires and discuss gaps in our knowledge about fate and transport, as well as the toxicology of tire particles and chemical leachates. We examine potential management and remediation approaches for addressing exposure risks across the life cycle of tires. We consider tires as pollutants across three levels: tires in their whole state, as particulates, and as a mixture of chemical cocktails. Finally, we discuss information gaps in our understanding of tires as a pollutant and outline key questions to improve our knowledge and ability to manage and remediate tire pollution.

Impacts of bio-stimulants on pyrene degradation, prokaryotic community compositions, and functions

Bio-stimulation of the indigenous microbial community is considered as an effective strategy for the bioremediation of polluted environments. This examination explored the near effects of various bio-stimulants on pyrene degradation, prokaryotic community compositions, and functions using 16S rRNA amplicon sequencing and qPCR. At first, the results displayed significant differences (p < 0.05) between the prokaryotic community structures of the control group, PYR (contains pyrene only), and bio-stimulants amended groups. Among the bio-stimulants, biochar, oxalic acid, salicylate, NPK, and ammonium sulfate augmented the pyrene degradation potential of microbial communities. Moreover, the higher abundance of genera, such as Flavobacterium, Hydrogenophaga, Mycobacterium, Rhodococcus, Flavihumibacter, Pseudomonas, Novosphingobium, etc., across the treatments indicated that these genera play a vital role in pyrene metabolism. Based on the higher abundance of GP-RHD and nidA genes, we speculated that Gram-positive prokaryotic communities are more competent in pyrene dissipation than Gram-negative. Furthermore, the marked abundance of nifH, and pqqC genes in the NPK and SA treatments, respectively, suggested that different bio-stimulants might enrich certain bacterial assemblages. Besides, the significant distinctions (p < 0.05) between the bacterial consortia of HA (humic acid) and SA (sodium acetate) groups from NPK, OX (oxalic acid), UR (urea), NH4, and SC (salicylate) groups also suggested that different bio-stimulants might induce distinct ecological impacts influencing the succession of prokaryotic communities in distinct directions. This work provides new insight into the bacterial degradation of pyrene using the bio-stimulation technique. It suggests that it is equally important to investigate the community structure and functions along with studying their impacts on degradation when devising a bio-stimulation technology.

Insight into Bacterial Community Responses to Polycyclic Aromatic Hydrocarbons and the Degradation Potentials of Three Bacterial Isolates in Seagrass Halophila ovalis Sediments

Seagrass meadows constitute a prestigious ecosystem in the marine environment, providing valuable ecological and commercial services. Among the various causes, pollutions are considered one of the significant reasons for seagrass decline globally. This study investigates the impacts of polycyclic aromatic hydrocarbons mixture (pyrene, phenanthrene, and fluorene) on bacterial communities in Halophila ovalis sediments. The seagrass sediment bacterial microbiome was evaluated in a batch culture experiment by Illumina MiSeq sequencing. Culture-able bacterial strains were isolated and characterized by 16S rRNA gene sequencing. The results demonstrated an excellent alpha diversity in the original sediments with a Shannon index of (8.078) compared to the subsequent control group (5.908) and PAH-treated group (PAH-T) (4.916). Three phyla, Proteobacteria, Firmicutes, and Bacteroidetes, were detected in high abundance in the control and PAH-T groups. However, a significant difference (P < 0.05) was observed at the genus level between control and PAH-T group bacterial consortia. Pseudomonas, Mycobacterium, Idiomarina, Hydrogenophaga, Alteromonas, Sphingobacterium, and several others were highly abundant in PAH-T groups. Most of the culture-able isolates recovered in this study showed the closest resemblance to previously identified hydrocarbon-degrading bacteria. Among the three strains, Mix-16 (Citricoccus yambaruensis) and Mix-20 (Gordonia rubripertincta) showed a higher degradation of PAHs than Mix-19 (Isoptericola halotolerans) in the monoculture experiment. The most increased degradation of PAHs was recorded in the co-culture experiment. The present work revealed that PAHs could act as environmental stress and can influence bacterial community succession. Moreover, the co-culture strategy significantly enhanced the biodegradation of PAHs.

Biotreatment of Cr(VI) and pyrene combined water pollution by loofa-immobilized bacteria

Hexavalent chromium (Cr(VI)) and pyrene are toxic pollutants that are difficult to remediate from soils and wastewater. Serratia sp. strains have been previously demonstrated to remove either Cr(VI) or pyrene and here a new isolate, called the Z6 strain, was demonstrated to remove both simultaneously. The removal occurs primarily by Cr(VI) reduction and pyrene biodegradation, and genome analysis suggests the removal mechanisms are the putative chromate reductase and two assumable pathways of pyrene degradation. The Z6 strain effectively removed most Cr(VI) (up to approximately 86%) and pyrene (up to approximately 57%) in seven different types of wastewater after 7 days of biotreatment. Additionally, the carrier loofa used for bacteria immobilization did not change the kinetics of Cr(VI) reduction or pyrene degradation. The carrier loofa was also effective for multiple uses, with removal capacity not being significantly affected over the first seven cycles with the same carrier loofa. These results provide data for developing practical biotreatment applications of Cr(VI) and pyrene contaminated sites.

Effect of pyrene and phenanthrene in shaping bacterial communities in seagrass meadows sediments

Polycyclic aromatic hydrocarbons (PAHs), originating from anthropogenic and natural sources, are highly concerned environmental pollutants. This study investigated the impact of two model PAHs (pyrene and phenanthrene) on bacterial community succession in the seagrass meadows sediment in a lab-scale microcosm. Halophila ovalis sediment slurry microcosms were established, one group was placed as a control, and the other two were treated with pyrene and phenanthrene. Bacterial community succession in response to respective PAHs was investigated by 16S rRNA amplicon sequencing. The results demonstrated that bacterial diversity decrease in each microcosm during the incubation process; however, the composition of bacterial communities in each microcosm was significantly different. Proteobacteria (37-89%), Firmicutes (9-41%), and Bacteroides (7-21%) were the predominant group at the phylum levels. Their abundance varies during the incubation process. Several previously reported hydrocarbon-degrading genera, such as Pseudomonas, Spinghobium, Sphingobacterium, Mycobacterium, Pseudoxanthomonas, Idiomarina, Stenotrophomonas, were detected in higher abundance in pyrene- and phenanthrene-treated microcosms. However, these genera were distinctly distributed in the pyrene and phenanthrene treatments, suggesting that certain bacterial groups favorably degrade different PAHs. Statistical analyses, such as ANOSIM and PERMANOVA, also revealed that significant differences existed among the treatments' bacterial consortia (P < 0.05). This work showed that polycyclic aromatic hydrocarbon significantly affects bacterial community succession, and different PAHs might influence the bacterial community succession differently.

Biotreatment of pyrene and Cr(VI) combined water pollution by mixed bacteria

Pyrene and chromium (Cr(VI)) are persistent pollutants and cause serious environmental problems because they are toxic to organisms and difficult to remediate. The toxicity of pyrene and Cr(VI) to three crops (cotton, soybean and maize) was confirmed by the significant decrease in root and shoot biomass during growth in pyrene/Cr(VI) contaminated hydroponic solution. Two bacterial strains capable of simultaneous pyrene biodegradation and Cr(VI) reduction were isolated and identified as Serratia sp. and Arthrobacter sp. A mixture of the isolated strains at a ratio of 1:1 was more efficient for biotreatment of pyrene and Cr(VI) than either strain alone; the mixture effectively carried out bioremediation of contaminated water in a hydroponic system mainly through pyrene biodegradation and Cr(VI) reduction. Application of these isolates shows potential for practical microbial remediation of pyrene and Cr(VI) combined water pollution.

A non-invasive method to monitor marine pollution from bacterial DNA present in fish skin mucus

Marine coastal contamination caused by human activity is a major issue worldwide. The implementation of effective pollution monitoring programs, especially in coastal areas, is important and urgent. The use of biological, physiological, or biochemical measurements to monitor the impacts of pollution has garnered increasing interest, particularly for the development of new non-invasive tools to assess water pollution. Fish skin mucus is in direct contact with the marine environment, making it a favourable microenvironment for the formation of biofilm bacterial communities. In this study, we developed a non-invasive technique, sampling fish skin mucus to determine and analyse bacterial community composition using next-generation sequencing. We hypothesised that bacterial communities associated with the skin mucus of a common harbour benthic blennioid triplefin fish, Forsterygion capito, would reflect conditions of different marine environments. We detected clear differences in bacterial community alpha-diversity between contaminated and reference sites. Beta-diversity analysis also revealed differences in the bacterial community structure of the skin mucus of fish inhabiting different geographical areas. The relative abundance of different bacterial orders varied among sites, as determined by linear discriminant analysis (LDA) and effect size (LEfSe) analyses. The observed variation in bacterial community compositions correlated more strongly with variation in hydrocarbons than to various metal concentrations. Using advanced DNA sequencing technologies, we have developed a novel non-invasive, low-cost and effective tool to monitor the impacts of pollution through analysis of the bacterial communities associated with fish skin mucus.

Acinetobacter sp. as the key player in diesel oil degrading community exposed to PAHs and heavy metals

The aim of this study was to verify the hypothesis that a hydrocarbon degrading community isolated from a site heavily polluted with polycyclic aromatic hydrocarbons (PAHs) and heavy metals should exhibit a high activity and biodegradation efficiency, despite decreased biodiversity resulting from the presence of such contaminants. Microbial community isolated from soil collected at an abandoned creosote railway wood-sleepers impregnation plant using diesel oil was used during the studies. Four parallel systems spiked with diesel oil, diesel oil + PAHs, diesel oil + heavy metals and diesel oil + PAHs + heavy metals were analysed in terms of relative abundance and biodiversity of the microbial community (Illumina), biodegradation efficiency (GCMS) and cellular metabolic activity (flow cytometry). Principal Component Analysis and biodiversity parameters indicated that the mixture of PAHs and heavy metals was the dominant factor which resulted in the enrichment of the Gammaproteobacteria class. This was associated with higher degradation of additional PAHs in the presence of heavy metals and an increase of metabolically active sub-populations during flow cytometry analysis. The increased abundance of the Acinetobacter genus in systems with both PAHs and heavy metals implies that it may play a crucial role in soil populations exposed to mixed contaminations.

Bacterial community assemblages in sediments under high anthropogenic pressure at Ichkeul Lake/Bizerte Lagoon hydrological system, Tunisia

Bacterial communities inhabiting sediments in coastal areas endure the effect of strong anthropogenic pressure characterized by the presence of multiple contaminants. Understanding the effect of pollutants on the organization of bacterial communities is of paramount importance in order to unravel bacterial assemblages colonizing specific ecological niches. Here, chemical and molecular approaches were combined to investigate the bacterial communities inhabiting the sediments of the Ichkeul Lake/Bizerte Lagoon, a hydrological system under anthropogenic pressure. Although the microbial community of the Ichkeul Lake sediment was different to that of the Bizerte Lagoon, common bacterial genera were identified suggesting a lake-lagoon continuum probably due to the hydrology of the system exchanging waters according to the season. These genera represent bacterial "generalists" maintaining probably general biogeochemical functions. Linear discriminant analysis effect size (LEfSe) showed significant differential abundance distribution of bacterial genera according to the habitat, the pollution type and level. Further, correlation analyses identified specific bacterial genera which abundance was linked with pesticides concentrations in the lake, while in the lagoon the abundance of specific bacterial genera was found linked with the concentrations of PAHs (Polycyclic aromatic hydrocarbons) and organic forms of Sn. As well, bacterial genera which abundance was not correlated with the concentrations of pollutants were identified in both lake and lagoon. These findings represent valuable information, pointing out specific bacterial genera associated with pollutants, which represent assets for developing bacterial tools for the implementation, the management, and monitoring of bioremediation processes to mitigate the effect of pollutants in aquatic ecosystems.

Nickel uptake and distribution in Agropyron cristatum L. in the presence of pyrene

PAHs affect the uptake of heavy metal by plants. The uptake pathway, distribution and detoxification of nickel (Ni) in Agropyron cristatum L. (A. cristatum) were investigated in the presence of pyrene in this study. Most of Ni was adsorbed on the cell wall in the insoluble phosphate (57.31-72.18%) form and pectate and protein integrated (38.27-38.98%) form. Ni was transferred to the organelle (from 37.84% to 40.52%) in the presence of pyrene. The concentration of Ni in A. cristatum decreased by 27.42%; it was affected by the ATP production inhibitor and 29.49% by the P-type ATPase inhibitor. The results indicated that the uptake of Ni related closely to the synthesis and decomposition of ATP and was an active uptake process. Contents of phytochelatins (PCs) in A. cristatum in Ni contaminated soils increased by 19.97%, and an additional 4.13% increase occurred in the presence of pyrene when compared to single Ni contamination. The content of malic acid in A. cristatum was the highest for 262.78 mg g^-1 in shoots and 46.81 mg g^-1 in roots with Ni contamination. Besides, acetic acid in shoots and roots increased by 40.25% and 102.63% with Ni contamination, and by 61.59% and 185.71% with Ni-pyrene co-contamination. This study preliminarily explored the inhibitory mechanism of pyrene on plant uptake of Ni.

Insights into mixed contaminants interactions and its implication for heavy metals and metalloids mobility, bioavailability and risk assessment

Mobility of heavy metals at contaminated sites is mainly influenced by the soil physicochemical properties and environmental conditions, therefore assessing heavy metals (HMs) and metalloids fractionation can provide insights into their potential risk and the mechanisms that regulate bioavailability. A 12-months mesocosms experiment was setup to investigate the effect of physicochemical factors (pH, moisture, and temperature) and weathering (time) on HMs and metalloids fractionation in three different multi-contaminated soil matrices (low, medium, and high contamination) collected from a soil treatment facility located in the United Kingdom, and two rural contaminated soil samples. The study demonstrates that even though Pb and Zn were found associated with the exchangeable fraction in the soil with the highest contamination (total average Pb 3400 mg/kg, and total average Zn 2100 mg/kg in Soil C), neither the condition applied nor the weathering caused an increase in their mobility. Although it was expected that lower pH (4.5) would favours the dissociation of HMs and metalloids, no significant differences were observed, potentially due to the initial alkaline pH of the genuine-contaminated soil samples. The results show that even though total concentration of Pb, Cu, and Zn exceed the soil standards and guideline values, HMs were predominantly associated with the non-exchangeable fraction, while only 5% were dissolved in the pore water fraction (potentially bioavailable). In addition, the mobility and bioavailability of HMs remained constant over the 12 months monitoring, suggesting that these soils pose negligible risk to the environment.

Polycyclic Aromatic Hydrocarbon (PAH) Degradation Pathways of the Obligate Marine PAH Degrader Cycloclasticus sp. Strain P1

Bacteria play an important role in the removal of polycyclic aromatic hydrocarbons (PAHs) from polluted environments. In marine environments, Cycloclasticus is one of the most prevalent PAH-degrading bacterial genera. However, little is known regarding the degradation mechanisms for multiple PAHs by CycloclasticusCycloclasticus sp. strain P1 was isolated from deep-sea sediments and is known to degrade naphthalene, phenanthrene, pyrene, and other aromatic hydrocarbons. Here, six ring-hydroxylating dioxygenases (RHDs) were identified in the complete genome of Cycloclasticus sp. P1 and were confirmed to be involved in PAH degradation by enzymatic assays. Further, five gene clusters in its genome were identified to be responsible for PAH degradation. Degradation pathways for naphthalene, phenanthrene, and pyrene were elucidated in Cycloclasticus sp. P1 based on genomic and transcriptomic analysis and characterization of an interconnected metabolic network. The metabolic pathway overlaps in many steps in the degradation of pyrene, phenanthrene, and naphthalene, which were validated by the detection of metabolic intermediates in cultures. This study describes a pyrene degradation pathway for Cycloclasticus. Moreover, the study represents the integration of a PAH metabolic network that comprises pyrene, phenanthrene, and naphthalene degradation pathways. Taken together, these results provide a comprehensive investigation of PAH metabolism in CycloclasticusIMPORTANCE PAHs are ubiquitous in the environment and are carcinogenic compounds and tend to accumulate in food chains due to their low bioavailability and poor biodegradability. Cycloclasticus is an obligate marine PAH degrader and is widespread in marine environments, while the PAH degradation pathways remain unclear. In this report, the degradation pathways for naphthalene, phenanthrene, and pyrene were revealed, and an integrated PAH metabolic network covering pyrene, phenanthrene, and naphthalene was constructed in Cycloclasticus This overlapping network provides streamlined processing of PAHs to intermediates and ultimately to complete mineralization. Furthermore, these results provide an additional context for the prevalence of Cycloclasticus in oil-polluted marine environments and pelagic settings. In conclusion, these analyses provide a useful framework for understanding the cellular processes involved in PAH metabolism in an ecologically important marine bacterium.

Polycyclic Aromatic Hydrocarbon (PAH) Degradation Pathways of the Obligate Marine PAH Degrader Cycloclasticus sp. Strain P1

Bacteria play an important role in the removal of polycyclic aromatic hydrocarbons (PAHs) from polluted environments. In marine environments, Cycloclasticus is one of the most prevalent PAH-degrading bacterial genera. However, little is known regarding the degradation mechanisms for multiple PAHs by Cycloclasticus Cycloclasticus sp. strain P1 was isolated from deep-sea sediments and is known to degrade naphthalene, phenanthrene, pyrene, and other aromatic hydrocarbons. Here, six ring-hydroxylating dioxygenases (RHDs) were identified in the complete genome of Cycloclasticus sp. P1 and were confirmed to be involved in PAH degradation by enzymatic assays. Further, five gene clusters in its genome were identified to be responsible for PAH degradation. Degradation pathways for naphthalene, phenanthrene, and pyrene were elucidated in Cycloclasticus sp. P1 based on genomic and transcriptomic analysis and characterization of an interconnected metabolic network. The metabolic pathway overlaps in many steps in the degradation of pyrene, phenanthrene, and naphthalene, which were validated by the detection of metabolic intermediates in cultures. This study describes a pyrene degradation pathway for Cycloclasticus. Moreover, the study represents the integration of a PAH metabolic network that comprises pyrene, phenanthrene, and naphthalene degradation pathways. Taken together, these results provide a comprehensive investigation of PAH metabolism in Cycloclasticus IMPORTANCE PAHs are ubiquitous in the environment and are carcinogenic compounds and tend to accumulate in food chains due to their low bioavailability and poor biodegradability. Cycloclasticus is an obligate marine PAH degrader and is widespread in marine environments, while the PAH degradation pathways remain unclear. In this report, the degradation pathways for naphthalene, phenanthrene, and pyrene were revealed, and an integrated PAH metabolic network covering pyrene, phenanthrene, and naphthalene was constructed in Cycloclasticus This overlapping network provides streamlined processing of PAHs to intermediates and ultimately to complete mineralization. Furthermore, these results provide an additional context for the prevalence of Cycloclasticus in oil-polluted marine environments and pelagic settings. In conclusion, these analyses provide a useful framework for understanding the cellular processes involved in PAH metabolism in an ecologically important marine bacterium.