Microscopy-based phenotypic profiling of infection by Staphylococcus aureus clinical isolates reveals intracellular lifestyle as a prevalent feature.

Staphylococcus aureus is increasingly recognized as a facultative intracellular pathogen, although the significance and pervasiveness of its intracellular lifestyle remain controversial. Here, we applied fluorescence microscopy-based infection assays and automated image analysis to profile the interaction of 191 S. aureus isolates from patients with bone/joint infections, bacteremia, and infective endocarditis, with four host cell types, at five times post-infection. This multiparametric analysis revealed that almost all isolates are internalized and that a large fraction replicate and persist within host cells, presenting distinct infection profiles in non-professional vs. professional phagocytes. Phenotypic clustering highlighted interesting sub-groups, including one comprising isolates exhibiting high intracellular replication and inducing delayed host death in vitro and in vivo. These isolates are deficient for the cysteine protease staphopain A. This study establishes S. aureus intracellular lifestyle as a prevalent feature of infection, with potential implications for the effective treatment of staphylococcal infections.

Snow Deposition and Melting as Drivers of Polychlorinated Biphenyls and Organochlorine Pesticides in Arctic Rivers, Lakes, and Ocean.

Concurrent sampling of freshwater (lakes and rivers), seawater, snow, air, and zooplankton for a range of legacy polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) was undertaken in the Canadian High Arctic during ice-covered, melting, and ice-free conditions. Overall, there was a general trend of higher fluvial PCB/OCP concentrations associated with the spring snow melt (early-mid June), while much lower concentrations were detected during the snow-free season (end of July). In contrast, PCB concentrations in two Arctic lakes (West and East Lakes, Melville Island) and in ocean waters, sharply increased in the ice-free period, likely because of inputs from the ice/snow layer melting and river runoff. The resulting air-water fugacity ratios and fluxes followed a remarkable shift during the sampling campaign. PCBs and OCPs shifted from equilibrium during ice/snow-covered conditions toward a clear net volatilization of PCBs and most of the OCPs during snow/ice-free conditions. Differences in the bioaccumulation factor for PCB/OCPs in zooplankton between West and East Lakes were observed, likely because of zooplankton being exposed to more contaminated food in West Lake due to higher turbidity related to in-lake disturbances.

Snow Amplification of Persistent Organic Pollutants at Coastal Antarctica.

Many legacy and emerging persistent organic pollutants (POPs) have been reported in polar regions, and act as sentinels of global pollution. Maritime Antarctica is recipient of abundant snow precipitation. Snow scavenges air pollutants, and after snow melting, it can induce an unquantified and poorly understood amplification of concentrations of POPs. Air, snow, the fugacity in soils and snow, seawater and plankton were sampled concurrently from late spring to late summer at Livingston Island (Antarctica). Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) concentrations in snow and air were close to equilibrium. POPs in soils showed concentrations close to soil-air equilibrium or net volatilization depending on chemical volatility. Seawater-air fugacity ratios were highly correlated with the product of the snow-air partition coefficient and the Henry's law constant (KSA H'), a measure of snow amplification of fugacity. Therefore, coastal seawater mirrored the PCB congener profile and increased concentrations in snowmelt due to snowpack releasing POPs to seawater. The influence of snowpack and glacier inputs was further evidenced by the correlation between net volatilization fluxes of PCBs and seawater salinity. A meta-analysis of KSA, estimated as the ratio of POP concentrations in snow and air from previously reported simultaneous field measurements, showed that snow amplification is relevant for diverse families of POPs, independent of their volatility. We claim that the potential impact of atmospheric pollution on aquatic ecosystems has been under-predicted by only considering air-water partitioning, as snow amplification influences, and may even control, the POP occurrence in cold environments.

Legacy and Emerging Persistent Organic Pollutants (POPs) in Terrestrial Compartments in the High Arctic: Sorption and Secondary Sources.

Legacy persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and emerging perfluoroalkyl substances (PFASs) were measured in vegetation and soil samples collected at remote lakes in the Canadian High Arctic. Field studies were carried out in 2015 and 2016 to assess concentrations of POPs, study the relevant sorbing phases, and determine whether Arctic soils were sinks or sources of legacy POPs to the atmosphere and to neighboring lakes. The patterns of legacy POPs in vegetation and soils were dominated by low molecular weight PCB congeners along with OCPs, confirming the importance of long-range atmospheric transport. Lipid and non-lipid organic matter was a key determinant of legacy POPs in Arctic vegetation. Soil organic matter was the main descriptor of hydrophobic PCBs and OCPs in soils, while soil inorganic carbon content, was an important driver of the sorption of PFASs in soils. While contaminant concentrations were low in soil and vegetation, higher PCBs and PFOS organic and inorganic carbon-normalized concentrations were found at Resolute Lake indicating the presence of local sources of contamination. Comparison of fugacities of PCBs in soil and air from Resolute Lake indicated soils as net sources of PCBs to the atmosphere.

Pivotal Role of Snow Deposition and Melting Driving Fluxes of Polycyclic Aromatic Hydrocarbons at Coastal Livingston Island (Antarctica).

The atmosphere-land-ocean dynamics of semivolatile organic compounds in polar regions is poorly understood, also for the abundant and ubiquitous polycyclic aromatic hydrocarbons (PAHs). We report the concentrations and fluxes of PAHs in a polar coastal ecosystem (Livingston Island, Antarctica). From late spring (December 2014) to late summer (February 2015), we sampled air, snow, coastal seawater, plankton, and the fugacity in soils and snow. The concentrations of PAHs in seawater were low but increased during the austral summer. The PAH concentrations in snow were significantly higher than in coastal seawater. Soil-air fugacity ratios showed a net volatilization of PAH when soils were covered with lichens, and close to air-soil equilibrium for bare soils. Concentrations in surface snow were also close to equilibrium with atmospheric PAHs. Conversely, there was a net diffusive deposition of PAHs to coastal seawater during late spring, but a net volatilization from seawater during late summer. Volatilization fluxes were correlated with seawater temperature and salinity, consistent with a key role of snowmelt to the fluxes and dissolved phase concentrations during the austral summer. The comprehensive assessment provided here shows that the fugacity amplification in snow is transferred to soils and coastal seawater supporting PAH concentrations and fluxes.

Climatic Influence on Temporal Trends of Polychlorinated Biphenyls and Organochlorine Pesticides in Landlocked Char from Lakes in the Canadian High Arctic.

Temporal trends and climate related parameters affecting the fate of legacy persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were examined in landlocked Arctic char from four lakes in the Canadian Arctic. Among biological parameters, lipid content was a key factor explaining the concentration of most POPs in Arctic char. Legacy PCBs and OCPs generally showed declining trends of concentrations in Arctic char, consistent with past restriction on uses and emissions of POPs. However, increases in lake primary productivity (measured as chlorophyll a) exerted a dilution effect on POPs concentrations in Arctic char. Concentrations of POPs in char from the last two decades were positively correlated with interannual variations of the North Atlantic Oscillation (NAO). Higher concentrations of POPs in Arctic char were observed in 3 of the 4 lakes during positive NAO phases. This, together with increasing local Arctic temperatures, could lead to increases on POPs concentrations in char from remote Arctic Lakes in future decades. Also, if there are nearby secondary sources as may be the case for Resolute Lake, located near an airport where increasing levels were found for hexachlorobenzene and toxaphene, probably due to the mobilization from secondary sources in soils.

Dissolved Organophosphate Esters and Polybrominated Diphenyl Ethers in Remote Marine Environments: Arctic Surface Water Distributions and Net Transport through Fram Strait.

Organophosphate esters (OPEs) have been found in remote environments at unexpectedly high concentrations, but very few measurements of OPE concentrations in seawater are available, and none are available in subsurface seawater. In this study, passive polyethylene samplers (PEs) deployed on deep-water moorings in the Fram Strait and in surface waters of Canadian Arctic lakes and coastal sites were analyzed for a suite of common OPEs. Total OPEs ( ∑11OPE) at deep-water sites were dominated by chlorinated OPEs, and ranged from 6.3 to 440 pg/L. Concentrations were similar in eastern and western Fram Strait. Chlorinated OPEs were also dominant in Canadian Arctic surface waters (mean concentration ranged from < DL to 4400 pg/L), while nonhalogenated alkyl/aryl-substituted OPEs remained low (1.3-55 pg/L), possibly due to the greater long-range transport potential of chlorinated OPEs. Polybrominated diphenyl ethers (PBDEs) were found at much lower concentrations than OPEs (

Anthropogenic and biogenic hydrocarbons in soils and vegetation from the South Shetland Islands (Antarctica).

Two Antarctic expeditions (in 2009 and 2011) were carried out to assess the local and remote anthropogenic sources of aliphatic and aromatic hydrocarbons, as well as potential biogenic hydrocarbons. Polycyclic aromatic hydrocarbons (PAHs), n-alkanes, biomarkers such as phytane (Ph) and pristane (Pr), and the aliphatic unresolved complex mixture (UCM), were analysed in soil and vegetation samples collected at Deception, Livingston, Barrientos and Penguin Islands (South Shetland Islands, Antarctica). Overall, the patterns of n-alkanes in lichens, mosses and grass were dominated by odd-over-even carbon number alkanes. Mosses and vascular plants showed high abundances of n-C21 to n-C35, while lichens also showed high abundances of n-C17 and n-C19. The lipid content was an important factor controlling the concentrations of n-alkanes in Antarctic vegetation (r(2)=0.28-0.53, p-level<0.05). n-C12 to n-C35 n-alkanes were analysed in soils with a predominance of odd C number n-alkanes (n-C25, n-C27, n-C29, and n-C31), especially in the background soils not influenced by anthropogenic sources. The large values for the carbon predominance index (CPI) and the correlations between odd alkanes and some PAHs suggest the potential biogenic sources of these hydrocarbons in Antarctica. Unresolved complex mixture and CPI values ~1 detected at soils collected at intertidal areas and within the perimeter of Juan Carlos research station, further supported the evidence that even a small settlement (20 persons during the austral summer) can affect the loading of aliphatic and aromatic hydrocarbons in nearby soils. Nevertheless, the assessment of Pr/n-C17 and Ph/n-C18 ratios showed that hydrocarbon degradation is occurring in these soils.

Validation and modelling of a novel diffusive sampler for determining concentrations of volatile organic compounds in air.

A novel diffusive sampler that combines radial and axial diffusion has been developed that improves upon existing commercially available designs. The POcket Diffusive (POD) sampler has been validated under laboratory and field conditions for the measurements of VOCs in ambient air. Laboratory tests varied sampling conditions of temperature (-30-40 C), humidity (10-80%), wind velocity (0.1-4 m s(-1)), and concentration (0.5-50 µg m(-3)) for a number of specific VOCs. An overall uncertainty of circa 9% for the measurement of benzene is calculated for the validation tests, in compliance with the data quality objectives of the EU air quality directive 2008/50/EC. A semi-empirical diffusion model has been developed to estimate sampling rates for compounds that were not tested, and for conditions outside of tested ranges during validation. The diffusion model (and validation tests) shows a low influence of environmental conditions on the sampling rate for the POD sampler. Average reproducibility values of circa 3% are reported with overall sampling uncertainties ranging from 9% to 15%, for the whole range of tested conditions, depending on the compound. The adsorbent cartridge is compatible with existing thermal desorption systems in the market. The diffusive sampler can modify the sampling rate by changing the diffusive body within a range of different porosities. Field tests, conducted in parallel with independent quality controlled canister sampling, confirmed the ease of use and quality of VOC measurements with the POD sampler, for compounds that were, and were not, evaluated during laboratory tests.

Unexpected occurrence of volatile dimethylsiloxanes in Antarctic soils, vegetation, phytoplankton, and krill.

Volatile methyl siloxanes (VMS) are high-production synthetic compounds, ubiquitously found in the environment of source regions. Here, we show for the first time the occurrence of VMS in soils, vegetation, phytoplankton, and krill samples from the Antarctic Peninsula region, which questions previous claims that these compounds are "flyers" and do not significantly reach remote ecosystems. Cyclic VMS are the predominant compounds, with concentrations ranging from the limits of detection to 110 ng/g in soils. Concentrations of cyclic VMS in phytoplankton are negatively correlated with sea surface salinity, indicating a source from ice and snow melting and consistent with snow depositional inputs. After the summer snow melting, VMS accumulate in the Southern Ocean and Antarctic biota. Therefore, once introduced into the marine environment, VMS are eventually trapped by the biological pump and, thus, behave as "single hoppers". Conversely, VMS in soils and vegetation behave as "multiple hoppers" due to their high volatility.

Climatic and biogeochemical controls on the remobilization and reservoirs of persistent organic pollutants in Antarctica.

After decades of primary emissions, reservoirs of persistent organic pollutants (POPs) have accumulated in soils and snow/ice in polar regions. These reservoirs can be remobilized due to decreasing primary emissions or due to climate change-driven warmer conditions. Results from a sampling campaign carried out at Livingston Island (Antarctica) focusing on field measurements of air-soil exchange of POPs show that there is a close coupling of the polychlorinated biphenyls (PCBs) in the atmosphere and snow/ice and soils with a status close to air-surface equilibrium to a net volatilization from Antarctic reservoirs. This remobilization of PCBs is driven by changes in temperature and soil organic matter (SOM) content, and it provides strong evidence that the current and future remobilization and sinks of POPs are a strong function of the close coupling of climate change and carbon cycling in the Antarctic region and this is not only due to warming. Whereas an increase of 1 °C in ambient temperature due to climate change would increase current Antarctic atmospheric inventories of PCBs by 21-45%, a concurrent increase of 0.5% SOM would counteract the influence of warming by reducing the POP fugacity in soil. A 1 °C increase in Antarctic temperatures will induce an increase of the soil-vegetation organic carbon and associated POPs pools by 25%, becoming a net sink of POPs, and trapping up to 70 times more POPs than the amount remobilized to the atmosphere. Therefore, changes in soil biogeochemistry driven by perturbations of climate may increase to a larger degree the soil fugacity capacity than the decrease in air and soil fugacity capacity due to higher temperatures. Future research should focus on quantifying these remobilization fluxes and sinks for the Antarctic region.

Biodegradation of phenanthrene by indigenous microorganisms in soils from Livingstone Island, Antarctica.

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soils has been linked to history of exposure to PAHs and prevailing environmental conditions. This work assessed the capacity of indigenous microorganisms in soils collected in Livingstone Island (South Shetlands Islands, Antarctica) with no history of pollution (∑PAHs: 0.14-1.47 ng g(-1) dw) to degrade (14) C-phenanhthrene at 4, 12 and 22 °C. The study provides evidence of the presence of phenanthrene-degrading microorganisms in all studied soils. Generally, the percentage of (14) C-phenanhthrene mineralized increased with increasing temperature. The highest extent of (14) C-phenanhthrene mineralization (47.93%) was observed in the slurried system at 22 °C. This work supports findings of the presence of PAH-degrading microorganisms in uncontaminated soils and suggests the case is the same for uncontaminated Antarctic remote soils.

Influence of organic matter content and human activities on the occurrence of organic pollutants in antarctic soils, lichens, grass, and mosses.

Banned pesticides such as HCB and p,p'-DDE, and other legacy and ongoing pollutants such as PCBs and PAHs, were measured in different vegetation types and soil samples collected at selected areas from Antarctic Peninsula (Deception and Livingstone Islands, Southern Shetlands). Two Antarctic expeditions (in 2005 and 2009) were carried out to assess POPs levels at remote areas, and close to current and abandoned Antarctic research settlements, to assess potential sources of pollutants. Overall, the patterns in lichens, mosses, and grass were dominated by low molecular PCB congeners and PAHs and the presence of HCB and p,p'-DDE rather than heavier compounds, suggesting the importance of long-range atmospheric transport of POPs as the main vector for the introduction of these chemicals to Antarctica. Statistically significant correlations (p-level < 0.05) between concentrations in vegetation of PCBs, p,p'-DDE, and the more volatile PAHs with lipid content were found with r(2) of 0.22-0.52 for PCBs, 0.42 for p,p'-DDE, and 0.44-0.72 for the more volatile PAHs. Thus, lipid content is an important factor controlling POPs in Antarctic lichens, mosses, and grass. A strong significant dependence of HCB (r(2) = 0.83), p,p'-DDE (r(2) = 0.60), and PCBs (r(2) = 0.36-0.47) concentrations in soil on its organic carbon content was also observed, indicating the important role of soil organic matter (SOM) in the retention of PCBs and OCPs in Polar Regions, where SOM content is low. Penguin colonies enhance the SOM content in some areas which is reflected in higher concentrations of all POPs, especially of persistent compounds such as p,p'-DDE. Higher concentrations of PCBs and PAHs found at the currently active Byers Camp (in an Antarctic Specially Protected Area) were explained by higher SOM content, thus indicating that Antarctic regulations are being successfully fulfilled in this small research area. On the other hand, PAHs in soils proximate to current Juan Carlos I research station show that even small human settlements are an important source of PAHs to the local environment. Therefore, even though the concentrations in Antarctica are low, there is evidence of local hotspots of contamination.

Ubiquitous net volatilization of polycyclic aromatic hydrocarbons from soils and parameters influencing their soil-air partitioning.

Soils are a major reservoir of organic pollutants, and soil-air partitioning and exchange are key processes controlling the regional fate of pollutants. Here, we report and discuss the soil concentrations of polycyclic aromatic hydrocarbons (PAHs), their soil fugacities, the soil-air partition coefficients (K(SA)) and soil-air gradients for rural and semirural soils, in background areas of N-NE Spain and N-NW England. Different sampling campaigns were carried out to assess seasonal variability and differences between sampling sites. K(SA) values were dependent on soil temperature and soil organic quantity and type. Soil fugacities of phenanthrene and its alkyl homologues were 1-2 orders of magnitude higher than their ambient air fugacities for all sampling sites and periods. The soil to air fugacity ratio was correlated with soil temperature and soil redox potential. Similar trends for other PAHs were found but with lower fugacity ratios. The ubiquitous source of PAHs from background soils to the atmosphere found in all temperate regions in different seasons provides an indirect evidence of potential in situ generation of two to four ring PAHs and their alkyl homologues in the surface soil. We discuss this hypothetical biogenic source and other potential processes that could drive the high soil to air fugacity ratios of some PAHs.

Factors influencing the soil-air partitioning and the strength of soils as a secondary source of polychlorinated biphenyls to the atmosphere.

Soils are a major reservoir of persistent organic pollutants, and soil-air partitioning and exchange are key processes controlling the atmospheric concentrations and regional fate of pollutants. Here, we report and discuss the concentrations of polychlorinated biphenyls (PCBs) in soils, their measured fugacities in soil, the soil-air partition coefficients (K(SA)) and soil-air fugacity gradients in rural background areas of N-NE Spain and N-NW England. Four sampling campaigns were carried out to assess seasonal and daily variability and differences between sampling sites. K(SA) values were significantly dependent on soil temperature and soil organic matter quantity, and to a minor extent organic matter type. All the PCB congeners in the soil are close to equilibrium with the atmosphere at rural Ebro sites, but soil fugacities tend to be higher than ambient air fugacities in early and late summer, consistent with the influence of temperature on soil-air partitioning. Therefore, during warm periods, soils increment their strength as secondary sources to the atmosphere. The mixture of PCBs found in the atmosphere is clearly strongly influenced by the mixture of PCBs which escape from soil, with significant correlations between them (R(2) ranging between 0.35 and 0.74 and p-level <0.001 for the Ebro sampling sites). Conversely, the close-to-equilibrium to net sink status of rural UK sites, suggest a close coupling of air and soil concentrations, but it is not possible to elucidate the importance of these soils as secondary sources yet, and presumably there are still significant primary sources to the regional/global environment.

Past, present, and future controls on levels of persistent organic pollutants in the global environment.

Understanding the legacy of persistent organic pollutants requires studying the transition from primary to secondary source control.

Development of a soil fugacity sampler for determination of air-soil partitioning of persistent organic pollutants under field controlled conditions.

Soils are the main reservoir of persistent organic pollutants (POPs) and thus air-soil exchange and partitioning are key processes controlling the fate and transport of POPs at regional and global scales. To date, soil fugacity has been estimated from models of the soil-air partition coefficients, with the associated unavoidable uncertainties; or by experimental procedures in the laboratory with uncertain application in field conditions. The development of an operational soil fugacity sampler is presented here; one which ensures optimal field data of the POP fugacity in soil and environmentally relevant surface (soil+grass, etc.) and therefore ensuring accurate soil-air partition coefficients and surface-air fugacity gradients. The sampler flow rate is optimized, sampler reproducibility is assessed, and equilibrium between the gas and soil concentrations of polychlorinated biphenyls and polycyclic aromatic hydrocarbons is demonstrated. The development and comprehensive validation of a soil fugacity sampler opens the door for the first time to field studies that accurately determine the variables driving the soil-air partitioning and fluxes of POPs.

Clustering of nonpolar organic compounds in lipid media: evidence and implications.

Semivolatile and nonpolar organic compounds, such as persistent organic pollutants, have a tendency to accumulate in organic matter phases from air and water. Once they enter living systems, they partition into lipids/waxes and can exert adverse toxicological effects. The current paradigm assumes that such chemicals are uniformly distributed in organic phases such as soil organic matter, plant waxes, and animal lipids and that partitioning and adsorption processes occur independently of intermolecular contaminant interactions. With use of a recently developed technique, two-photon excitation microscopy coupled with autofluorescence allowed us to directly visualize novel organic chemical behavior in living vegetation and other matrixes. Here, we show for the first time that polycyclic aromatic hydrocarbons, which were uniformly distributed in pure oils and waxes at the beginning of a study, form clusters over time. The number and diameter (typically 0.2-5 microm) of these clusters are dependent on the physical-chemical properties of the compound-media systems and time. This behavior is not accounted for in current models of phase partitioning of chemicals and may have important implications for understanding their environmental fate and their potential toxicological effects.