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The temporal trend of polycyclic aromatic hydrocarbons (PAHs) in coastal waters with highly dynamic sources and sinks is largely unknown, especially for polar regions. Here, we show the concurrent measurements of 73 individual PAHs and environmental data, including the composition of the bacterial community, during three austral summers at coastal Livingston (2015 and 2018) and Deception (2017) islands (Antarctica). The Livingston 2015 campaign was characterized by a larger snow melting input of PAHs and nutrients. The assessment of PAH diagnostic ratios, such as parent to alkyl-PAHs or LMW to HMW PAHs, showed that there was a larger biodegradation during the Livingston 2015 campaign than in the Deception 2017 and Livingston 2018 campaigns. The biogeochemical cycling, including microbial degradation, was thus yearly dependent on snow-derived inputs of matter, including PAHs, consistent with the microbial community significantly different between the different campaigns. The bivariate correlations between bacterial taxa and PAH concentrations showed that a decrease in PAH concentrations was concurrent with the higher abundance of some bacterial taxa, specifically the order Pseudomonadales in the class Gammaproteobacteria, known facultative hydrocarbonoclastic bacteria previously reported in degradation studies of oil spills. The work shows the potential for elucidation of biogeochemical processes by intensive field-derived time series, even in the harsh and highly variable Antarctic environment., This work has been supported by the Spanish Ministry of Science and Innovation (MCIN) through projects REMARCA (CTM2012-34673), SENTINEL (CTM2015-70535), ANTOM (PGC2018-096612-B-100), MIQAS (PID2021-128084OB-I00), and PANTOC (PID2021-127769NB-I00). J. Iriarte acknowledges the predoctoral FPU fellowship (FPU19/02782) funded by the Spanish Ministry of Universities. Dr. Daniel Lundin is acknowledged for his support in bioinformatic analyses. The research group of Global Change and Genomic Biogeochemistry receives support from the Catalan Government (2017SGR800). IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S).

The large-scale use of organophosphate esters (OPEs) as flame retardants and plasticizers has led to their prevalence in the environment, with still unknown broader impacts. This Review describes the transport and occurrence of OPEs in marine systems and summarizes emerging evidence of their biogeochemical and ecosystem impacts. Long-range environmental transport via the atmosphere and ocean currents distributes OPEs from industrialized regions to the open ocean. OPEs are most prevalent in coastal regions, but notable concentrations are also found in the Arctic and regions far from shore. Air–water interactions are important for the transport of OPEs to remote oceans and polar regions. Processes such as degradation and sinking of particle-bound compounds modulate the properties and fate of OPEs in the water column, where they are potentially a non-accounted source of anthropogenic organic phosphorus for microbial communities. Some OPEs have toxic effects in marine species and are found in measurable quantities in fish and other aquatic organisms. However, there is conflicting evidence on the potential for bioaccumulation and biomagnification of OPEs. Future work must constrain the large-scale impact of OPEs on marine biota and biogeochemistry to support more effective regulation and mitigation., The authors are very grateful to D. Muir for his detailed and constructive internal review on the manuscript. They thank W. Cheng and R. Zhang for providing the data on OPEs in air, snow and marine organisms. They thank Q. Meng, L. Mi and J. Li for technical support in creating Figs 1–4. Z.X. acknowledges the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 689443 via project iCUPE (Integrative and Comprehensive Understanding on Polar Environments). They thank the researchers who contributed original research for OPEs in environmental and biological matrices and modelling predictions.

13 pages, 5 figures, supporting information https://doi.org/10.1021/acs.est.0c07262, Coastal seawaters receive thousands of organic pollutants. However, we have little understanding of the response of microbiomes to this pool of anthropogenic dissolved organic carbon (ADOC). In this study, coastal microbial communities were challenged with ADOC at environmentally relevant concentrations. Experiments were performed at two Mediterranean sites with different impact by pollutants and nutrients: off the Barcelona harbor (“BCN”), and at the Blanes Bay (“BL”). ADOC additions stimulated prokaryotic leucine incorporation rates at both sites, indicating the use of ADOC as growth substrate. The percentage of “membrane-compromised” cells increased with increasing ADOC, indicating concurrent toxic effects of ADOC. Metagenomic analysis of the BCN community challenged with ADOC showed a significant growth of Methylophaga and other gammaproteobacterial taxa belonging to the rare biosphere. Gene expression profiles showed a taxon-dependent response, with significantly enrichments of transcripts from SAR11 and Glaciecola spp. in BCN and BL, respectively. Further, the relative abundance of transposon-related genes (in BCN) and transcripts (in BL) correlated with the number of differentially abundant genes (in BCN) and transcripts (in BLA), suggesting that microbial responses to pollution may be related to pre-exposure to pollutants, with transposons playing a role in adaptation to ADOC. Our results point to a taxon-specific response to low concentrations of ADOC that impact the functionality, structure and plasticity of the communities in coastal seawaters. This work contributes to address the influence of pollutants on microbiomes and their perturbation to ecosystem services and ocean health., This work was supported by the Spanish Ministry of Economy and Competitiveness (MEIC) through projects ISOMICS (CTM2015-65691-R) and REMARCA (CTM2012-34673). E.C.G. was supported by Agència de Gestió d’Ajuts Universtaris i Recerca, Generalitatde Catalunya (FI AGAUR) Scholarship, Generalitat de Catalunya Fellowship Program (Catalan Government, Generalitat de Catalunya) and by a “FORD ESPAÑA-APADRINA LA CIENCIA” contract. The research group of Global Change and Genomic Biogeochemistry is supported by the Catalan Government (2017SGR800). We thank Dr. J. M. Gasol for support with flow cytometry counts. Inorganic nutrient analyses were performed by M. I. Abad in coordination with Dr. E. Berdalet (Head of the Service) at the “Nutrient Analysis Service of the ICM-CSIC. Dr Piña is acknowledged for fruitful discussions., With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI).

Semivolatile organic pollutants have potential for long range atmospheric transport and can thus reach pristine remote lakes by atmospheric deposition. Polycyclic aromatic hydrocarbons (PAHs) are among the most abundant and toxic semivolatile pollutants affecting lakes, however, the main factors controlling their fate are still poorly known. Here we show two contrasting lines of evidence for the importance of microbial degradation on the environmental fate of PAHs in a high altitude deep lake. The first evidence is given by an assessment of the metagenomes from surface and deep waters from Lake Redon (Pyrenees Mountains), which shows the occurrence of the initial ring hydroxylating dioxygenases as well as other PAH degrading genes from the complete metabolic route of PAH degradation. The second line of evidence is by the application of an environmental fate model for PAHs to Lake Redon under two contrasting scenarios considering the inclusion or not of degradation. When degradation is included in the model, PAH concentrations in the sediment are predicted within a factor of two of those measured in Lake Redon. Finally, the extent of the degradation sink is quantified and compared to other cycling PAH fluxes in the lake., This work was supported by the Spanish MEIC through project ISOMICS (CTM2015-65691-R). The research group of Global Change and Genomic Biogeochemistry is supported by the Catalan Government (2017SGR800). IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S).

Increasing resolution has always been a goal for environmental chemistry and toxicology in their quest to expand knowledge on the transport, biogeochemistry, and sinks of natural- and anthropogenic chemicals in the environment, as well as their functions and effects in ecosystem and human health. Linking biology and chemistry is at the core of environmental sciences, (1) and it is now possible to study comprehensive cell signatures by means of single-cell approaches. The trend toward the analysis of increasingly smaller samples, eventually reaching nanosamples and even single-cell approaches, (1−5) has resulted in massive data sets. The measures at cellular level, at higher temporal and spatial scale resolution, require significant methodological development, but allows for new questions with eventual knowledge breakthroughs.

Scavenging of gas- and aerosol-phase organic pollutants by rain is an efficient wet deposition mechanism of organic pollutants. However, whereas snow has been identified as a key amplification mechanism of fugacities in cold environments, rain has received less attention in terms of amplification of organic pollutants. In this work, we provide new measurements of concentrations of perfluoroalkyl substances (PFAS), organophosphate esters (OPEs), and polycyclic aromatic hydrocarbons (PAHs) in rain from Antarctica, showing high scavenging ratios. Furthermore, a meta-analysis of previously published concentrations in air and rain was performed, with 46 works covering different climatic regions and a wide range of chemical classes, including PFAS, OPEs, PAHs, polychlorinated biphenyls and organochlorine compounds, polybromodiphenyl ethers, and dioxins. The rain–aerosol (KRP) and rain–gas (KRG) partition constants averaged 105.5 and 104.1, respectively, but showed large variability. The high field-derived values of KRG are consistent with adsorption onto the raindrops as a scavenging mechanism, in addition to gas–water absorption. The amplification of fugacities by rain deposition was up to 3 orders of magnitude for all chemical classes and was comparable to that due to snow. The amplification of concentrations and fugacities by rain underscores its relevance, explaining the occurrence of organic pollutants in environments across different climatic regions., We thank the staff of the Marine Technology Unit (UTM-CSIC) for their logistical support during the sampling campaign at Livingston Island, M. Pizarro for technical assistance, and The State Meteorological Agency (AEMET) for the meteorological assistance. This work was supported by Spanish Ministry of science to G.C. and A.M.-V. through predoctoral fellowships and projects SENTINEL (CTM2015-70535-P) and ANTOM (PGC2018-096612-B-l00). This research is part of POLARCSIC activities. The research group of Global Change and Genomic Biogeochemistry receives support from the Catalan Government (2017SGR800). Special thanks to TERNUA for sponsoring technical eco-friendly clothing and gear equipment for Antarctic campaigns.

Thousands of man-made synthetic chemicals are released to oceans and compose the anthropogenic dissolved organic carbon (ADOC). Little is known about the effects of this chronic pollution on marine microbiome activities. In this study, we measured the pollution level at three sites in the Northeast Subarctic Pacific Ocean (NESAP) and investigated how mixtures of three model families of ADOC at different environmentally relevant concentrations affected naturally occurring marine bacterioplankton communities' structure and metabolic functioning. The offshore northernmost site (North) had the lowest concentrations of hydrocarbons, as well as organophosphate ester plasticizers, contrasting with the two other continental shelf sites, the southern coastal site (South) being the most contaminated. At North, ADOC stimulated bacterial growth and promoted an increase in the contribution of some Gammaproteobacteria groups (e.g. Alteromonadales) to the 16 rRNA pool. These groups are described as fast responders after oil spills. In contrast, minor changes in South microbiome activities were observed. Gene expression profiles at Central showed the coexistence of ADOC degradation and stress-response strategies to cope with ADOC toxicities. These results show that marine microbial communities at three distinct domains in NESAP are influenced by background concentrations of ADOC, expanding previous assessments for polar and temperate waters., This publication is dedicated to the memory of our missed friend, mentor and colleague, Prof. Ronald P. Kiene. The authors thank the Capitan and crew of the R/V Oceanus. This work was funded by the Spanish MEIC through projects ISOMICS (CTM2015-65691-R) and SENTINEL (CTM2015-70535-P). The authors sincerely thank J.M. Gasol for support with flow cytometry counts and I. Forn for microscopy counts. The research group of Global Change and Genomic Biogeochemistry is supported by the Catalan Government (2017SGR800). IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S)., With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI).

Thousands of synthetic chemicals and hydrocarbons are released to the marine environment composing the anthropogenic dissolved organic carbon (ADOC). Most ADOC is disproportionally hydrophobic, and consequently, its concentrations in the cell membranes are between a thousand and hundred million fold higher than those in the dissolved phase. Marine microorganisms respond to ADOC by multiple strategies ranging from ADOC degradation to detoxifying metabolisms. We argue that the increasing concentrations of ADOC in the oceans deriving from rivers, atmospheric deposition, and plastic leachates can have an effect on the health of the oceans and influence the major biogeochemical cycles, thus influencing the Earth system during the Anthropocene. Human activity dramatically changes the chemosphere through contribution of synthetic compounds, as well as unnatural mobilization processes, such as industrial scale hydrocarbon extraction, combustion, and agriculture. Millions of man-made chemicals have been synthesized, of which 300,000 are currently under commerce [1]. Man-made chemicals include flame retardants, pesticides, herbicides, pharmaceuticals, musk fragrances, surfactants, sealants, plastics, plasticizers, and other plastic exudates, dioxins, food additives, antibiotics, among others. These synthetic chemicals, together with hydrocarbons associated with the extraction and use of fossil fuels, have been released to the environment during the Anthropocene following an exponential growth. As an example, it is estimated that the use of plastics during the past 15 years only, surpasses that used during the previous century [2]. On the other hand, current emissions of hydrocarbons coming from incomplete combustion of fossil fuels, such as those of polycyclic aromatic hydrocarbons, are significantly higher than in preindustrial ages. All together, these thousands of hydrocarbons and synthetic organic chemicals at trace levels are continuously shaping the contemporaneous Earth chemosphere, including the marine environment. While coastal seawater is impacted by rivers and continental runoff leading to widespread occurrence of synthetic chemicals, such as plastic leachates, there is also a diffuse pollution to the global oceans by atmospheric deposition, which can account for large carbon fluxes (e.g., 400 TgC year−1 for aromatic hydrocarbons only, [3], Supplementary Fig. 1). Once in seawater, synthetic chemicals and hydrocarbons compose the anthropogenic dissolved organic carbon (ADOC). The components of ADOC comprise relatively well-studied chemicals, such as hydrocarbons, polychlorinated biphenyls, perfluoroalkyl substances, and organophosphate esters, among other chemicals and mixtures contributing to ADOC (Supplementary Table 1). Similar to the natural dissolved organic carbon (DOC), there are ADOC compounds of labile, semilabile, and refractory nature, the latter known as persistent organic pollutants. Turnover rates of ADOC components in marine systems can range from hours to centuries, but are poorly characterized for most chemicals. The known pool of ADOC is generally

Thousands of semi-volatile hydrophobic organic pollutants (OPs) reach open oceans through atmospheric deposition, causing a chronic and ubiquitous pollution by anthropogenic dissolved organic carbon (ADOC). Hydrophobic ADOC accumulates in cellular lipids, inducing harmful effects on marine biota, and can be partially prone to microbial degradation. Unfortunately, their possible effects on microorganisms, key drivers of global biogeochemical cycles, remain unknown. We challenged coastal microbial communities from Ny-Ålesund (Arctic) and Livingston Island (Antarctica) with ADOC concentrations within the range of oceanic concentrations in 24 h. ADOC addition elicited clear transcriptional responses in multiple microbial heterotrophic metabolisms in ubiquitous groups such as Flavobacteriia, Gammaproteobacteria and SAR11. Importantly, a suite of cellular adaptations and detoxifying mechanisms, including remodelling of membrane lipids and transporters, was detected. ADOC exposure also changed the composition of microbial communities, through stimulation of rare biosphere taxa. Many of these taxa belong to recognized OPs degraders. This work shows that ADOC at environmentally relevant concentrations substantially influences marine microbial communities. Given that emissions of organic pollutants are growing during the Anthropocene, the results shown here suggest an increasing influence of ADOC on the structure of microbial communities and the biogeochemical cycles regulated by marine microbes. © 2019 Society for Applied Microbiology and John Wiley & Sons Ltd., This work was supported by BBVA Foundation for Researchers and Cultural Creative Workers award to MVC (14_CMA_020) and by the Spanish Ministerio de Economía y Competitividad (Ministry of Economy and Competitiveness, MEIC) through projects ISOMICS (CTM2015‐65691‐R), REMARCA (CTM2012‐34673) and SENTINEL (CTM2015‐70535‐P). ECG was supported by Agència de Gestió d'Ajuts Universtaris i Recerca, Generalitat de Catalunya (FI AGAUR) Scholarship, Generalitat de Catalunya Fellowship Program (Catalan Government, Generalitat de Catalunya). We thank MC. Fernández‐Pinos, M. Pizarro and G. Caballero for assistance with experimental settings, I. Forn, Dr. R. Massana and Dr. JM Gasol for support with CARD‐FISH and flow cytometry counts. Dr. C. Galbán‐Malagón (U. Andres‐Bello) for providing POP concentrations in polar seawater. The research group of Global Change and Genomic Biogeochemistry is supported by the Catalan Government (2017SGR800).

Dissolved black carbon (DBC) plays a role in the oceanic carbon cycle. DBC originates from the heating and incomplete combustion of organic matter, including fossil fuels, a shared origin with polycyclic aromatic hydrocarbons (PAH). DBC is quantified using the benzene polycarboxylic acids produced by oxidation of the organic extract, a fraction of which derive from PAHs and other semivolatile aromatic-like compounds (SALCs). However, the current view of the DBC cycle does not take into account the inputs and sinks known for PAHs, such as diffusive air–water exchange and degradation. A meta-analysis of oceanic PAHs, SALCs, and DBC concentrations shows that SALCs account for 16% of DBC (ranging from 5% to 31%). Such a large contribution of semivolatile aromatic hydrocarbons to DBC is consistent with the large atmospheric input of SALCs (estimated as 400 Tg C y–1). Furthermore, photodegradation at the surface ocean and microbial degradation in the water column of semivolatile DBC can be important sinks, consistent with the ubiquitous occurrence of the degradation genes of the metabolic routes for aromatic hydrocarbons. Future work should focus on the characterization of semivolatile DBC and its degradation in order to constrain its contribution to refractory organic matter and the anthropogenic perturbation of the carbon cycle., This work was supported by the ANTOM project funded by the Spanish Research Agency from the Ministry of Science (PGC2018-096612-B-I00). N.T. and G.C. acknowledge FPI Ph.D. fellowships from the Spanish Research Agency. The research group of Global Change and Genomic Biogeochemistry receives support from the Catalan Government (2017SGR800). This research is part of POLARCSIC activities. IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S).

The composition of bacteria inhabiting the sea-surface microlayer (SML) is poorly characterized globally and yet undescribed for the Southern Ocean, despite their relevance for the biogeochemistry of the surface ocean. We report the abundances and diversity of bacteria inhabiting the SML and the subsurface waters (SSL) determined from a unique sample set from a polar coastal ecosystem (Livingston Island, Antarctica). From early to late austral summer (January–March 2018), we consistently found a higher abundance of bacteria in the SML than in the SSL. The SML was enriched in some Gammaproteobacteria genus such as Pseudoalteromonas, Pseudomonas, and Colwellia, known to degrade a wide range of semivolatile, hydrophobic, and surfactant-like organic pollutants. Hydrocarbons and other synthetic chemicals including surfactants, such as perfluoroalkyl substances (PFAS), reach remote marine environments by atmospheric transport and deposition and by oceanic currents, and are known to accumulate in the SML. Relative abundances of specific SML-enriched bacterial groups were significantly correlated to concentrations of PFASs, taken as a proxy of hydrophobic anthropogenic pollutants present in the SML and its stability. Our observations provide evidence for an important pollutant-bacteria interaction in the marine SML. Given that pollutant emissions have increased during the Anthropocene, our results point to the need to assess chemical pollution as a factor modulating marine microbiomes in the contemporaneous and future oceans., This work was supported by the Spanish Ministry of Science to GC and AM-V through predoctoral fellowships, and through projects SENTINEL (CTM2015-70535-P) and ISOMICS (CTM2015-65691-R). This research was part of POLARCSIC activities. The research group of Global Change and Genomic Biogeochemistry receives support from the Catalan Government (2017SGR800).

The accumulation of Perfluoroalkyl substances (PFAS) in the SML and their enrichment in SSA is consistent with marine aerosols as a vector for PFAS transport.Sea-spray (or sea-salt) aerosol (SSA) formation and their subsequent atmospheric transport and deposition have been suggested to play a prominent role in the occurrence of ionizable perfluoroalkyl substances (PFAS) in the maritime Antarctica and other remote regions. However, field studies on SSA's role as vector of transport of PFAS are lacking. Following a multiphase approach, seawater (SW), the sea-surface microlayer (SML) and SSA were sampled simultaneously at South Bay (Livingston Island, Antarctica). Average PFAS concentrations were 313 pg L, 447 pg L, and 0.67 pg m in SW, the SML and SSA, respectively. The enrichment factors of PFAS in the SML and SSA ranged between 1.2 and 5, and between 522 and 4690, respectively. This amplification of concentrations in the SML is consistent with the surfactant properties of PFAS, while the large enrichment of PFAS in atmospheric SSA may be facilitated by the large surface area of SSA and the sorption of PFAS to aerosol organic matter. This is the first field work assessing the simultaneous occurrence of PFAS in SW, the SML and SSA. The large measured amplification of concentrations in marine aerosols supports the role of SSA as a relevant vector for long-range atmospheric transport of PFAS., the mass of PFAS and Naþin SSA are in line with reported mea-surements. Such large enrichment factors in SSA have also beendescribed for experiments simulating the formation of SSA underlaboratory conditions (Reth et al., 2011). Underfield conditions,Casal et al. (2017a,2017b)has shown that the profile of PFCA inAntarctic fresh snow is particularly enriched with long-chain PFCA,consistent with the results reported here of high EFSSAfor PFOA,PFNA and PFDA. As snowflakes scavenge aerosols during deposi-tion, the large concentrations of PFAS in SSA are consistent withsnow deposition being a relevant source of PFAS in cold environ-ments, and SSA are an important source of PFAS to snow.As far as we know, this is thefirstfield study reporting thesimultaneous measurements of PFAS in SW, the SML and SSA. Eventhough there is some enrichment of PFAS at the SML of the surfaceocean, most of the large concentrations of PFAS in marine aerosolare due to the amplification of concentration during the formationof SSA. Such amplification of concentrations by more than twoorders of magnitude can be facilitated by various processes relatedto the accumulation of PFAS at the surface of the sea and aerosols. Ithas been suggested that SSA can be inverse micelles (Ellison et al.,1999;Gerard et al., 2016;Tervahattu et al., 2002). The criticalmicelle concentration for PFOA is of 0.00885 M (3.7 109ng L1)(Reth et al., 2011), thus orders of magnitude higher than PFOAconcentrations in the SML and in SSA. The targeted PFAS aredissociated at marine pH, acting as amphiphilic surfactants, butPFAS alone cannot form micelles in SSA by their own. However,marine aerosols are often coated with an OM layer (Tervahattuet al., 2002). PFAS can be part of this layer of lipids (fatty acids,hydrocarbons) in SSA or being adsorbed onto it. PFAS could be partof micelles together with surfactant-like OM, abundant in the SMLand SSA, but the confirmation of this would require future work.SSA have a large surface area, much larger than the SML. Assuminga thickness of 100mm for the SML, 1 L of SML water corresponds to10 m2of sea surface. On the other hand, SSA have sizes rangingfrom 0.01mmto1mm(Johansson et al., 2019), which means that 1 Lof SSAs having these aerosol sizes have a surface area of 600,000 m2and 6000 m2, respectively. Thus, SSA has a surface area between600 and 60,000 that of the SML, consistent with EFSSAorders ofmagnitude larger than EFSML. The large variability of EFSSAmay bethe result to different sizes of SSA and different characteristics ofthe highly variable SML. These issues will require further researchin order to improve the models for the long-range transport of PFASto Antarctica and elsewhere.4. ConclusionsPFAS were found to be ubiquitous in SW, the SML and SSA inSouth Bay from Livingston Island (southern Shetlands), a repre-sentative environment of the maritime Antarctica. Nevertheless,there were some differences in the relative abundance of PFAS inthe different matrixes, with PFSA and PFCA with carbon number ofC4 and C6, or C6 and C8eC10, respectively, being dominant in theSML and the underlying waters. High concentrations of PFBA werefound in SSA. The enrichment factors in the SML and SSA, defined asthe ratio of concentrations in the SML or SSA and that of SW,respectively, ranged between 1.2 and 5, and between 522 and 4692.The enrichment of PFAS in the SML is consistent with the amphi-philic properties of PFAS and their moderate hydrophobicity. Thelarge amplification of concentrations in SSA may be due to the largesurface area of SSA, the formation of inverse micelles by the largeamounts of surfactant like OM present in SSA, which may includePFAS and other organic compounds present in the SML, or tosorption of PFAS to OM present in SSA. The efficient transfer of PFASfrom the ocean to the atmosphere through the formation of SSAmay be relevant for atmospheric long-range transport of PFAS toAntarctica and other remote environments.Author statementGemma Casas: Conceptualization, Methodology, Formal anal-ysis, Investigation, Writing Original draft, Writing review&editing.Alicia Martinez-Varela: Methodology, Investigation. Jose LuisRoscales: Methodology, Investigation. Maria Vila-Costa: Method-ology, Investigation. Jordi Dachs: Conceptualization, Formal anal-ysis, Investigation, Writing review&editing. Bego~na Jimenez:Conceptualization, Methodology, Investigation, writing review&editing.Declaration of competing interestThe authors declare that they have no known competingfinancial interests or personal relationships that could haveappeared to influence the work reported in this paper.AcknowledgmentsWe thank the staff of the Marine Technology Unit (UTM-CSIC)for their logistical support during the sampling campaign at Liv-ingston Island, and M. Pizarro for technical assistance. This workwas supported by Spanish Ministry of science to GC and AMVthrough predoctoral fellowships, and through projects SENTINEL(CTM 2015-70535-P) and ISOMICS (CTM 2015-65691-R). This research is part of POLARCSIC activities. The research group of Global Change and Genomic Biogeochemistry receives support from the Catalan Government (2017SGR800). Special thanks toTERNUA for their non profit collaboration by sponsoring with technical ecofriendly clothing and gear equipment for Antarctic campaigns

The use of treated wastewater for crop irrigation is rapidly increasing to respond to the ever-growing demands for water and food resources. However, this practice may contribute to the spread of antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs) in agricultural settings. To evaluate this potential risk, we analyzed microbiomes and resistomes of soil and Lactuca sativa L. (lettuce) root samples from pots irrigated with tap water spiked with 0, 20, or 100 μg L of a mixture of three antibiotics (Trimethoprim, Ofloxacin, Sulfamethoxazole). The presence of antibiotics induced changes in bacterial populations, particularly in soil, as revealed by 16S rDNA sequence analysis. Parallel shotgun sequencing identified a total of 56 different ARGs conferring resistance against 14 antibiotic families. Antibiotic -treated samples showed increased loads of ARGs implicated in mutidrug resistance or in both direct and indirect acquired resistance. These changes correlated with the prevalence of Xantomonadales species in the root microbiomes. We interpret these data as indicating different strategies of soil and root microbiomes to cope with the presence of antibiotics, and as a warning that their presence may increase the loads of ARBs and ARGs in edible plant parts, therefore constituting a potential risk for human consumers., Francisco Cerqueira acknowledges the staff from the Agricultural Research Institute and NIREAS Research Center for their support during his secondment at the University of Cyprus, and making the experiment possible.

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., Inorganic nutrient analyses were performed by Mrs. M. I. Abad in coordination with Dr. E. Berdalet (Head of the Service) at the “Nutrient Analysis Service” of the ICM (CSIC). We thank F. Cerqueria and A. Martinez for support with DNA analysis. This work was supported by Spanish Ministry of Science to P.C. through a predoctoral fellowhip, by Fundación BBVA award to M.V.C., European Commission to A.C. through a Marie Curie international outgoing fellowship, and by the Spanish MINECO through projects REMARCA (CTM2012- 34673) and ISOMICS (CTM2015-65691-R). The research group of Global Change and Genomic Biogeochemistry is supported by the Catalan Government (2017SGR800).

13 pages, 5 figures, 2 tables, supplementary material https://doi.org/10.1016/j.scitotenv.2019.04.361, Organic pollutants are continuously being introduced in seawater with uncharacterized impacts on the engines of the marine biogeochemical cycles, the microorganisms. The effects on marine microbial communities were assessed for perfluoroalkyl substances, organophosphate esters flame retardants and plasticizers, polycyclic aromatic hydrocarbons, and n-alkanes. Dose-response experiments were performed at three stations and at three depths in the NW Mediterranean with contrasted nutrient and pollutant concentrations. In these experiments, the microbial growth rates, the abundances of the main bacterial groups, measured by Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD-FISH), and extracellular enzymatic activities, were quantified. Increasing concentrations of organic pollutants (OPs)promoted different responses in the communities that were compound, organism and nutrient availability (trophic status). The largest differences between OP treatments and controls in the growth rates of both heterotrophic and phototrophic microbial groups were observed in seawater from the deep chlorophyll maxima. Furthermore, there was a compound specific stimulation of different extracellular enzymatic activities after the exposure to OPs. Our results revealed that marine microbial communities reacted not only to hydrocarbons, known to be used as a carbon source, but also to low concentrations of organic pollutants of emerging concern in a complex manner, reflecting the variability of various environmental variables. Multiple linear regressions suggested that organic pollutants modulated the bacterial growth and extracellular enzymatic activities, but this modulation was of lower magnitude than the observed pronounced response of the microbial community to nutrient availability, This work has been financed by the Spanish Ministry of Economy and Competitiveness through projects ISOMICS (CTM2015-65691-R), DO-RE-MI (CTM2012-34294), ANIMA (CTM2015-65720-R) and REMEI (CTM2015-70340-R) and by Fundación BBVA award to MVC. ECG acknowledges a FI fellowship from the Generalitat de Catalunya (AGAUR)

The anthropogenic perturbation of the phosphorus (P) marine biogeochemical cycle due to synthetic organophosphorus compounds remains unexplored. The objective of this work was to investigate the microbial degradation of organophosphate triesters (OPEs), widely used as plasticizers and flame retardants, in seawater and their effects on the physiology and composition of microbial communities. Experiments were performed in July 2014 using surface seawater from the Blanes Bay Microbial Observatory (NW Mediterranean) to which OPEs were added at environmentally relevant concentrations. The concentrations of OPEs in the dissolved-phase generally decreased after 24 hours of incubation at in situ conditions. The fitted first order reaction constants were significantly different than zero for the trihaloalkyl phosphate, tris(2-chloroethyl) phosphate and trialyl phosphate tricresyl phosphate. In general, OPEs triggered an increase of the percentage of actively respiring bacteria, total bacterial activity, and the number of low-nucleic acid bacteria, and a decrease in the percentage of membrane-compromised bacteria. Members of some bacterial groups, in particular Flavobacteria, increased their specific activity, indicating that seawater contains bacteria with the potential to degrade OPEs. In aged seawater that was presumably depleted of labile dissolved organic carbon and inorganic P, alkaline phosphatase activities significantly decreased when OPEs were added, indicating a relief on P stress, consistent with the role of OPEs as potential P sources. © 2019, The Author(s)., This work was supported by Fundación BBVA award to MVC and by the Spanish MEIC through projects ISOMICS (CTM2015-65691-R) and REMEI (CTM2015-70340-R). MS was supported by grant EcoRARE (CTM2014-60467-JIN), funded by the Spanish Government and the European Regional Development Fund (ERDF) and a Viera y Clavijo contract funded by the ACIISI and the ULPGC. The research group of Global Change and Genomic Biogeochemistry is supported by the Catalan Goverment (2017SGR800). We thank J Castro-Jimenez for support on the OPE analyses. MVC is indebted to J Pinhassi for support.

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 (K 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 K, 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., We thank the staff of the Marine Technology UNIT (UTMCSIC) for their logistical support during the sampling campaign at Livingston Island. This work was supported by Spanish Ministry of science to P.C. through a predoctoral fellowship, European Commission to A.C. through a Marie Curie international outgoing fellowship, and by the Spanish MINECO through projects REMARCA (CTM2012-34673), SENTINEL (CTM2015-70535-P), and ISOMICS (CTM2015-65691-R). This research is part of POLARCSIC activities. The research group of Global Change and Genomic Biogeochemistry receives support from the Catalan Government (2017SGR800).

Atmospheric deposition of semivolatile aromatic hydrocarbons accounts for an important input of organic matter to the surface ocean. Nevertheless, the biogeochemical cycling and sinks of semivolatile aromatic hydrocarbons in the ocean remain largely uncharacterized. Here we present measurements of 64 polycyclic aromatic hydrocarbons in plankton and seawater from the Atlantic, Pacific, Indian and Southern Oceans, as well an assessment of their microbial degradation genes. Concentrations of the more hydrophobic compounds decreased when the plankton biomass was higher, consistent with the relevance of the biological pump. The mass balance for the global oceans showed that the settling fluxes of aromatic hydrocarbons in the water column were two orders of magnitude lower than the atmospheric deposition fluxes. This imbalance was high for low molecular weight hydrocarbons, such as phenanthrene and methylphenanthrenes, highly abundant in the dissolved phase. Parent polycyclic aromatic hydrocarbons were depleted to a higher degree than alkylated polycyclic aromatic hydrocarbons, and the degradation genes for polycyclic aromatic hydrocarbons were found to be ubiquitous in oceanic metagenomes. These observations point to a key role of biodegradation in depleting the bioavailable dissolved hydrocarbons and to the microbial degradation of atmospheric inputs of organic matter as a relevant process for the marine carbon cycle., The authors thank the support of the RV Hespérides staff and UTM technicians during the cruise and Antarctic campaign. G. Caballero and M. J. Ojeda are acknowledged for technical support during the extraction and processing of the samples. This work was funded by the Spanish Government through the Malaspina 2010 (CSD2008-00077), REMARCA (CTM2012-34673), SENTINEL (CTM2015-70535-P) and ISOMICS (CTM2015-65691-R) projects. M.V.-C. acknowledges a Leonardo award from BBVA Foundation. Predoctoral fellowships from the Spanish government (A.M.-V. and P.C.), Catalan government (E.C.-G.), Spanish Oceanography Institute (C.M.) and BBVA Foundation (B.G.-G.) are acknowledged. B.G.-G., A.M.-V., M.V.-C., P.C., E.C.-G., N.B. and J.D. belong to the “Global Change and Genomic Biogeochemistry” research group funded by the Catalan Government (2017SGR800).

7 páginas, 3 figuras, Human-induced ocean acidification impacts marine life. Marine bacteria are major drivers of biogeochemical nutrient cycles and energy fluxes1; hence, understanding their performance under projected climate change scenarios is crucial for assessing ecosystem functioning. Whereas genetic and physiological responses of phytoplankton to ocean acidification are being disentangled2–4, corresponding functional responses of bacterioplankton to pH reduction from elevated CO2 are essentially unknown. Here we show, from metatranscriptome analyses of a phytoplankton bloom mesocosmexperiment, that marine bacteria responded to lowered pH by enhancing the expression of genes encoding proton pumps, such as respiration complexes, proteorhodopsin and membrane transporters. Moreover, taxonomic transcript analysis showed that distinct bacterial groups expressed di erent pH homeostasis genes in response to elevated CO2. These responses were substantial for numerous pH homeostasis genes under low-chlorophyll conditions (chlorophyll a20 g l1) were low. Given that proton expulsion through pH homeostasis mechanisms is energetically costly, these findings suggest that bacterioplankton adaptation to ocean acidification could have long-term e ects on the economy of ocean ecosystems., This research was financially supported by grants from the Göran Gustafsson Foundation for Research in Natural Sciences and Medicine, the Swedish Research Council VR, the Swedish Research Council FORMAS strong research programme EcoChange, and the BONUS BLUEPRINT project, which has received funding from BONUS, the joint Baltic Sea research and development programme (Art 185), funded jointly from the European Union's Seventh Programme for research, technological development and demonstration and from the Swedish Research Council FORMAS to J.Pinhassi. The research was also financially supported by the SpanishMinistry of Science and Innovation project DOREMI (CTM2012-34294) to C.M. and J.M.Gasol, and by project CTM2013-48292-C3-3-R to J.M.Gasol.

Root functional diversity of submerged vegetation exerts a major effect on nitrogen (N) cycling in lake sediments. This fact, however, is neglected in current N-balance models because the links between the engineering role of plants and in situ microbial N cycling are poorly understood. We hypothesized that macrophyte species with high root oxygen loss (ROL) capacity promote the highest denitrification because of a higher abundance of ammonia oxidizers and tighter coupling between nitrifiers and denitrifier communities. We sampled five small ultraoligotrophic shallow lakes with abundant macrophyte cover including sediments dominated either by Isoetes spp. (high ROL), mixed communities of natopotamids (low ROL), and unvegetated sandy sediments. At each site, we quantified denitrification (DNT) rates and proxies for the abundance of denitrifiers (nirS and nirK genes), and both ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) and the diversity of nirS-harboring bacteria. Vegetated sediments showed significantly higher abundances of N-cycling genes than bare sediments. Plant communities dominated by Isoetes generated sediments with higher redox and NO3− concentrations and significantly higher DNT rates than natopotamids-dominated landscapes. Accordingly, increasing DNT rates were observed along the gradient from low ROL plants-bare sediments-high ROL plants. Significantly higher abundance of the archaeal amoA gene was recorded in sediments colonized by high ROL plants unveiling a key biogeochemical role for AOA in coupling macrophyte landscape and ecosystem denitrification.

Este artículo contiene 9 páginas, 5 figuras, 1 tabla., Two of the main mechanisms of bacterial resistance to sulfonamides in aquatic systems, spread of antibiotic resistance genes (ARG) among the microbial community and in-situ bacterial sulfonamide degradation, were studied in mesocosms experiments using water and cobble biofilms from upstream (pristine waters) and downstream (polluted waters) from the Llobregat river, NE Iberian Peninsula. Mesocosms were prepared at two different concentrations (5000 ng/L and 1000 ng/L) of sulfonamides antibiotics (sulfamethazine and sulfamethoxazole). Concentrations of ARG, nutrients, sulfonamides and their degradation products were measured during the time course of the experiments. Sulfonamides were efficiently degraded by the biofilms during the first four weeks of the experiment. The abundance of ARG in biofilms sharply decreased after addition of high concentrations of sulfonamides, but this was not observed in the mesocosms treated with low concentrations of sulfonamides. Sulfonamide degradation was faster in polluted waters and at high concentrations of sulfonamide (and lower ARG abundances), suggesting that both degradation and ARG are two complementary resistance strategies employed by the microbial community. This study shows that microbial degradation of antibiotics is an efficient resistance mechanism coupled with the presence of ARG, and suggests that in situ degradation prevails at high concentrations of antibiotics whereas physiological adaptation by ARG spread would be more important under relatively lower concentrations of antibiotics., This work has been supported by Marie Curie ActionsdIntra- European Fellowships (IEF), project number 275863 and by the Spanish Ministry of Economy and Competitiveness project DARKNESS CGL2012-32747 to E.O.C.

Polyamines (PAs) are a group of nitrogen-rich dissolved organic nitrogen (DON) compounds that are ubiquitously distributed in marine environments. To identify bacteria that are involved in PA transformations, coastal bacterioplankton microcosms were amended with a single PA model compound, i.e. putrescine (PUT) or spermidine (SPD), or with no addition as controls (CTRs). Bromodeoxyuridine (BrdU) was added to all the microcosms to label newly synthesized DNAs. Fluorescence-activated cell sorting (FACS) analysis indicated significant increases in numbers of total cells and cells with both high and low levels of BrdU incorporation in the PUT and SPD microcosms, but not in the CTRs. 16S rDNA pyrotag sequencing of FACS-sorted cells indicated that PUT- and SPD-transforming bacteria were composed similarly of a diverse group of taxa affiliated with Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria (especially Roseobacter of its alpha lineage). Broad taxonomic distribution of PA-transforming bacteria was also indicated by the abundance and distribution of PA transporter gene homologues in a survey of sequenced marine bacterial genomes. Our results suggest that PAs may be common DON substrates for marine bacterioplankton, in line with the hypothesis that bacterially mediated PA transformation accounts for an important proportion of marine DON flux.

Bacterial degradation of dimethylsulfoniopropionate (DMSP) represents one of the main sources of the climatically–active trace gas dimethylsulfide (DMS) in the upper ocean. Short-term enrichment studies to stimulate specific pathways of DMSP degradation in oligotrophic waters from the Sargasso Sea were used to explore regulatory connections between the different bacterial DMSP degradation steps and determine potential biological controls on DMS formation in the open ocean. Experiments were conducted with surface water at the BATS station in the western North Atlantic Ocean. We added selected organic substrates (25 nmol L−1 final concentration) to induce different steps of DMSP degradation in the microbial community, and then measured DMSP dynamics (assimilation and turnover rates), DMS yields (using 35sulfur-DMSP tracer), and bacterial production rates. In most treatments, the main fate of consumed S-DMSP was excretion as a non-volatile S product. 35S-DMSP tracer turnover rates (accumulation + assimilation + excretion of transformed products as DMS or others) increased upon addition of DMSP and glucose, but not acrylate, methymercaptopropionate (MMPA), methanethiol, DMS or glycine betaine. DMS yields from 35S-DMSP never exceeded 16 % except in a short term DMSP enrichment, for which the yield reached 45 % (±17 %). Results show that availability of non-sulfur containing labile C sources (glucose, acrylate) decreased bacterial DMS production while stimulating bacterial heterotrophic production, and suggest an influence of bacterial sulfur demand in controlling DMS-yielding pathways. However, regulatory effects on 35S-DMSP fate were not consistent across all reduced sulfur compounds (i.e., methanethiol or MMPA), and may reflect alternate roles of DMSP as a bacterial energy source and osmolyte.

[1] Dimethylsulfide (DMS) is a biogenic gas with potential climatic effects, and its marine emission depends on the interplay between microbial activity and physical forcing in the oceanic upper mixed layer. We investigated the diel cycling patterns of DMS and its precursor dimethylsulfoniopropionate (DMSP) in four experiments (28 to 48 h long) performed in mesotrophic to ultraoligotrophic Mediterranean and Sargasso Sea waters. Samples taken every 4 or 6 h were analyzed for dimethylated sulfur pools and incubated to measure DMS and DMSP cycling rates, as well as primary and bacterial production. In all four experiments, DMS budgets showed pronounced day versus night variability. In the three summer experiments, gross community DMS production (GPDMS) increased by twofold to threefold from nighttime to daytime, peaking 0–4 h after solar noon. This excess GPDMS was balanced by higher photochemical and microbial sinks during the day, effectively buffering DMS concentrations. In the only winter experiment, GPDMS exhibited opposed temporal dynamics and peaked at nighttime in parallel to total DMSP consumption. Community DMSP to DMS conversion yields were generally 15% (even >50%) during the day in summer, presumably due to phytoplankton radiative stress. Our data suggest that (1) diel variability should be taken into account in process studies, diagnostic, and prognostic models of DMS cycling and (2) the community DMS yield is a key variable that defines characteristic DMS cycling regimes.

The ecological significance of the marine bacterial populations distinguishable by flow cytometry on the basis of the fluorescence (FL) of their nucleic acid (NA) content and proxies of cell size (such as side scatter, SSC) remains largely unknown. Some studies have suggested that cells with high NA (HNA) content and high SSC (HS) represent the active members of the community, while the low NA (LNA) cells are inactive members of the same phylogenetic groups. But group-specific activity measurements and phylogenetic assignment after cell sorting have suggested this is not be the case, particularly in open-ocean communities. To test the extent to which the different NA subgroups are similar, and consequently the extent to which they likely have similar ecological and biogeochemical roles in the environment, we analysed the phylogenetic composition of three populations after cell sorting [high NA-high SC (HNA-HS), high NA-low SC (HNA-LS), low NA (LNA)] by 454 pyrosequencing in two contrasting periods of the year in NW Mediterranean coastal waters (BBMO, Blanes Bay Microbial Observatory) where these three populations have recurrent seasonal patterns. Statistical analyses showed that summer and winter samples were significantly different and, importantly, the sorted populations within a sample were composed of different taxa. The majority of taxa were associated with one NA fraction only, and the degree of overlap (i.e. OTUs present simultaneously in 2 fractions) between HNA and LNA and between summer and winter communities was very small. Rhodobacterales, SAR116 and Bacteroidetes contributed primarily to the HNA fraction, whereas other groups such as SAR11 and SAR86 contributed largely to the LNA fractions. Gammaproteobacteria other than SAR86 showed less preference for one particular NA fraction. An increase in diversity was observed from the LNA to the HNA-HS fraction for both sample dates. Our results suggest that, in Blanes Bay, flow cytometric signatures of natural communities track their phylogenetic composition.

11 páginas, 4 figuras., Dimethylsulfoniopropionate (DMSP) is an important source of reduced sulfur and carbon for marine microbial communities, as well as the precursor of the climate-active gas dimethylsulfide (DMS). In this study, we used metatranscriptomic sequencing to analyze gene expression profiles of a bacterial assemblage from surface waters at the Bermuda Atlantic Time-series Study (BATS) station with and without a short-term enrichment of DMSP (25 nm for 30 min). An average of 303 143 reads were obtained per treatment using 454 pyrosequencing technology, of which 51% were potential protein-encoding sequences. Transcripts from Gammaproteobacteria and Bacteroidetes increased in relative abundance on DMSP addition, yet there was little change in the contribution of two bacterioplankton groups whose cultured members harbor known DMSP degradation genes, Roseobacter and SAR11. The DMSP addition led to an enrichment of transcripts supporting heterotrophic activity, and a depletion of those encoding light-related energy generation. Genes for the degradation of C3 compounds were significantly overrepresented after DMSP addition, likely reflecting the metabolism of the C3 component of DMSP. Mapping these transcripts to known biochemical pathways indicated that both acetyl-CoA and succinyl-CoA may be common entry points of this moiety into the tricarboxylic acid cycle. In a short time frame (30 min) in the extremely oligotrophic Sargasso Sea, different gene expression patterns suggest the use of DMSP by a diversity of marine bacterioplankton as both carbon and sulfur sources., This study was funded by a Marie Curie Fellowship (to MVC), the Gordon and Betty Moore Foundation, and the National Science Foundation (OCE0724017 to MAM and OCE0425166 to J Dacey and D Toole)

Data from several years of monthly samplings are combined with a 1-year detailed study of carbon flux through bacteria at a NW Mediterranean coastal site to delineate the bacterial role in carbon u ...

13 pages, 6 figures, The contribution of major phylogenetic groups to heterotrophic bacteria assimilating sulfur from dissolved dimethylsulfoniopropionate (DMSP) and assimilating leucine was analysed in surface seawaters from Blanes Bay (NW Mediterranean) over an annual study between March 2003 and April 2004. The percentage of bacteria assimilating DMSP-S showed a strong seasonal pattern, with a steady increase from winter (8 ± 5%) to summer (23 ± 3%). The same seasonal pattern was observed for the rate of DMSP-S assimilation. The annual average percentage of DMSP-S-assimilating bacteria (16 ± 8%) was lower than the corresponding percentage of leucine-assimilating cells (35 ± 16%), suggesting that not all bacteria synthesizing protein incorporated DMSP-S. Smaller differences between both percentages were recorded in summer. Members of the Alphaproteobacteria (Roseobacter and SAR11) and Gammaproteobacteria groups accounted for most of bacterial DMSP-S-assimilating cells over the year. All major bacterial groups showed an increase of the percentage of cells assimilating DMSP-S during summer, and contributed to the increase of the DMSP-S assimilation rate in this period. In these primarily P-limited waters, enrichment with P + DMSP resulted in a stimulation of bacterial heterotrophic production comparable to, or higher than, that with P + glucose in summer, while during the rest of the year P + glucose induced a stronger response. This suggested that DMSP was more important a S and C source for bacteria in the warm stratified season. Overall, our results suggest that DMSP-S assimilation is controlled by the contribution of DMSP to S (and C) sources rather than by the phylogenetic composition of the bacterioplankton, This work was supported by the Spanish Ministry of Education and Science through a PhD studentship to M.V.-C, and through the projects MicroDIFF and MODIVUS (contracts REN2001-2120/MAR anc DTM2005-04795/MAR to J.M.G), by the Catalan government through Grant 2005SGR00021 (to R.S.) and by th EU's 5th Framework Program through project BASICs (contract EVK3-CT-2002-00078 to J.M.G.)

12 pages, 4 figures, 3 tables, supplementary data http://femsec.oxfordjournals.org/content/suppl/2015/05/31/fiv058.DC1, Bacterioplankton communities are made up of a small set of abundant taxa and a large number of low-abundant organisms (i.e. 'rare biosphere'). Despite the critical role played by bacteria in marine ecosystems, it remains unknown how this large diversity of organisms are affected by human-induced perturbations, or what controls the responsiveness of rare compared to abundant bacteria. We studied the response of a Mediterranean bacterioplankton community to two anthropogenic perturbations (i.e. nutrient enrichment and/or acidification) in two mesocosm experiments (in winter and summer). Nutrient enrichment increased the relative abundance of some operational taxonomic units (OTUs), e.g. Polaribacter, Tenacibaculum, Rhodobacteraceae and caused a relative decrease in others (e.g. Croceibacter). Interestingly, a synergistic effect of acidification and nutrient enrichment was observed on specific OTUs (e.g. SAR86). We analyzed the OTUs that became abundant at the end of the experiments and whether they belonged to the rare (1% relative abundance) fractions. Most of the abundant OTUs at the end of the experiments were abundant, or at least common, in the original community of both experiments, suggesting that ecosystem alterations do not necessarily call for rare members to grow, The experiments were funded by projects ACDC (CTM2009-08849, to EC and CP), STORM (CTM2009-09352/MAR, to CM and JMG) and ECOBAF (CTM2010-10462-E/MAR, to JMG). FB was supported by an University of Otago Research Grant (UORG). The diversity work was supported by projects from the European Science Foundation (EuroEEFG project MOCA) and the Swedish Research Council to JP

14 páginas, 7 figuras, 3 tablas., Stratified sulfurous lakes are appropriate environments for studying the links between composition and functionality in microbial communities and are potentially modern analogs of anoxic conditions prevailing in the ancient ocean. We explored these aspects in the Lake Banyoles karstic area (NE Spain) through metagenomics and in silico reconstruction of carbon, nitrogen and sulfur metabolic pathways that were tightly coupled through a few bacterial groups. The potential for nitrogen fixation and denitrification was detected in both autotrophs and heterotrophs, with a major role for nitrogen and carbon fixations in Chlorobiaceae. Campylobacterales accounted for a large percentage of denitrification genes, while Gallionellales were putatively involved in denitrification, iron oxidation and carbon fixation and may have a major role in the biogeochemistry of the iron cycle. Bacteroidales were also abundant and showed potential for dissimilatory nitrate reduction to ammonium. The very low abundance of genes for nitrification, the minor presence of anammox genes, the high potential for nitrogen fixation and mineralization and the potential for chemotrophic CO2 fixation and CO oxidation all provide potential clues on the anoxic zones functioning. We observed higher gene abundance of ammonia-oxidizing bacteria than ammonia-oxidizing archaea that may have a geochemical and evolutionary link related to the dominance of Fe in these environments. Overall, these results offer a more detailed perspective on the microbial ecology of anoxic environments and may help to develop new geochemical proxies to infer biology and chemistry interactions in ancient ecosystems., This research was funded by Grants GOS-LAKES CGL2009-08523-E and DARKNESS CGL2012-32747 to EOC from the Spanish Office of Science (MINECO), from financial support by the Beyster Family Fund of the San Diego Foundation and the Life Technologies Foundation to the J Craig Venter Institute, and the NASA Astrobiology Institute to CLD.

7 páginas, 7 figuras, To date different electrode materials have been used to improve the performance and reduce the costs of microbial fuel cells (MFCs). Particularly, there is a need to avoid the use of expensive Pt-based cathode materials. Here, we explored the use of vertically aligned carbon nanotubes (CNTs) deposited by plasma-enhanced chemical vapor deposition as cathode material in single chamber MFCs. In order to improve cell performance and lower the oxygen reduction reaction resistance at the cathode side, MnO2 catalyst was electrochemically deposited on the CNTs. Results show an increase in the output voltage and power density by two orders of magnitude when compared to plain stainless-steel electrodes, with a maximum power density of 24 mW m-2. Furthermore, the influence of medium solution in the electrolyte was also examined. Results demonstrate that microbial communities developed as biofilm in the anode were limited by substrate metabolic liability. The presence of a labile organic source (acetate) promoted an increase of one order of magnitude in cell performance. Overall, this study shows the potential of aligned CNTs to increase yield of MFCs., This work was supported by projects 2009SGR00185 of AGAUR of Generalitat de Catalunya and CTQ2009-14674-CO2-01 and MAT2010-20468 from MICINN of Spanish Government. The authors thank Centres Cientı´fics i Tecnolo` gics de la Universitat de Barcelona (CCiTUB) for measurement facilities and EDAR Sant Feliu de Llobregat for providing wastewater samples.

12 pages, 5 figures, 2 tables, supplementary material http://onlinelibrary.wiley.com/doi/10.1111/j.1462-2920.2006.01102.x/suppinfo, Microbial consumption is one of the main processes, along with photolysis and ventilation, that remove the biogenic trace gas dimethylsulfide (DMS) from the surface ocean. Although a few isolates of marine bacteria have been studied for their ability to utilize DMS, little is known about the characteristics or phylogenetic affiliation of DMS consumers in seawater. We enriched coastal and open-ocean waters with different carbon sources to stimulate different bacterial communities (glucose-consuming bacteria, methyl group-consuming bacteria and DMS consumers) in order to test how this affected DMS consumption and to examine which organisms might be involved. Dimethylsulfide consumption was greatly stimulated in the DMS addition treatments whereas there was no stimulation in the other treatments. Analysis of microbial DNA by two different techniques (sequenced bands from DGGE gels and clone libraries) showed that bacteria grown specifically with the presence of DMS were closely related to the genus Methylophaga. We also followed the fate of consumed DMS in some of the enrichments. Dimethylsulfide was converted mostly to DMSO in glucose or methanol enrichments, whereas it was converted mostly to sulfate in DMS enrichments, the latter suggesting use of DMS as a carbon and energy source. Our results indicate that unlike the biochemical precursor of DMS, dimethylsulfoniopropionate (DMSP), which is consumed by a broad spectrum of marine microorganisms, DMS seems to be utilized as a carbon and electron source by specialists. This is consistent with the usual observation that DMSP turns over at much higher rates than DMS, This work was supported by a PhD fellowship from the Spanish Ministry of Education to M.V. Field work was supported by NSF through the Biocomplexity in the Environment program (OPP 0221748; P. Matrai, P.I.) and by the Spanish MEC through project CAOS (CTM2004-20022-E). The molecular work was funded by projects MICRODIFF (REN2001-2120/MAR), BASICS (EVK3-CT-2002-00078) and GENµMAR (CTM2004-02586/MAR)

Polyamines (PAs) are a group of nitrogen-rich dissolved organic nitrogen (DON) compounds that are ubiquitously distributed in marine environments. To identify bacteria that are involved in PA transformations, coastal bacterioplankton microcosms were amended with a single PA model compound, i.e. putrescine (PUT) or spermidine (SPD), or with no addition as controls (CTRs). Bromodeoxyuridine (BrdU) was added to all the microcosms to label newly synthesized DNAs. Fluorescence-activated cell sorting (FACS) analysis indicated significant increases in numbers of total cells and cells with both high and low levels of BrdU incorporation in the PUT and SPD microcosms, but not in the CTRs. 16S rDNA pyrotag sequencing of FACS-sorted cells indicated that PUT- and SPD-transforming bacteria were composed similarly of a diverse group of taxa affiliated with Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria (especially Roseobacter of its alpha lineage). Broad taxonomic distribution of PA-transforming bacteria was also indicated by the abundance and distribution of PA transporter gene homologues in a survey of sequenced marine bacterial genomes. Our results suggest that PAs may be common DON substrates for marine bacterioplankton, in line with the hypothesis that bacterially mediated PA transformation accounts for an important proportion of marine DON flux.

10 páginas, 3 figuras, 3 tablas., Microbial biofilms in oligotrophic environments are the most reactive component of the ecosystem. In highaltitude lakes, exposed bedrock, boulders, gravel, and sand in contact with highly oxygenated water and where a very thin epilithic biofilm develops usually dominate the littoral zone. Traditionally, these surfaces have been considered unsuitable for denitrification, but recent investigations have shown higher biological diversity than expected, including diverse anaerobic microorganisms. In this study, we explored the presence of microbial N-cycling nirS and nirK (denitrification through the conversion of NO2 − to NO), nifH (N2 fixation), anammox (anaerobic ammonium oxidation), and amoA (aerobic ammonia oxidation, both bacterial and archaeal) genes in epilithic biofilms of a set of high-altitude oligotrophic lakes in the Pyrenees. The concentrations of denitrifying genes determined by quantitative PCR were two orders of magnitude higher than those of ammonia-oxidizing genes. Both types of genes were significantly correlated, suggesting a potential tight coupling nitrification-denitrification in these biofilms that deserves further confirmation. The nifH gene was detected after nested PCR, and no signal was detected for the anammoxspecific genes used. The taxonomic composition of denitrifying and nitrogen-fixing genes was further explored by cloning and sequencing. Interestingly, both microbial functional groups were richer and more genetically diverse than expected. The nirK gene, mostly related to Alphaproteobacteria (Bradyrhizobiaceae), dominated the denitrifying gene pool as expected for oxygen-exposed habitats, whereas Deltaproteobacteria (Geobacter like) and Cyanobacteria were the most abundant among nitrogen fixers. Overall, these results suggest an epilithic community more metabolically diverse than previously thought and with the potential to carry out an active role in the biogeochemical nitrogen cycling of highaltitude ecosystems. Measurements of activity rates should be however carried out to substantiate and further explore these findings., This study was supported by MINECO grants DARKNESS (CGL2012-32747) to EOC and NITROPIR (CGL2010-19373) to JC.

The polyamines putrescine (PUT) and spermidine (SPD) are ubiquitous in seawater, but mechanisms that drive the degradation of these important nitrogen sources by marine bacteria remain unclear. We employed a comparative metatranscriptomics approach to compare gene transcription patterns between coastal bacterioplankton communities with and without amendments of PUT or SPD, in an effort to understand how bacterial communities and their genes shape polyamine biogeochemistry in the ocean. Statistically different transcript categories in the PUT (25 COG groups) and SPD (23 COG groups) samples, relative to controls that received no amendment (CTRL), indicated that genes encoding the cellular translation machinery and the metabolism of organic nitrogen and carbon became enriched in the community transcriptome when polyamine availability increased. Of the three known pathways for bacterial polyamine degradation, only genes in the transamination pathway were enriched in the PUT and SPD libraries, suggesting that this route dominated polyamine degradation. Taxonomic affiliation of significantly enriched diagnostic genes in the PUT and SPD libraries pointed to roseobacter- and SAR11-affiliated bacteria as the predominant taxa driving transformation in this coastal ocean, although other diverse marine bacterioplankton groups (Gammaproteobacteria, Betaproteobacteria, Actinobacteria and Bacteroidetes) also contributed to polyamine-related gene transcription.

Electrode optimization in microbial fuel cells is a key issue to improve the power output and cell performance. Vertically aligned carbon nanotubes (VACNTs) grown on low cost stainless-steel mesh present an attractive approach to increase the cell performance while avoiding the use of expensive Pt-based materials. In comparison with non-aligned carbon nanotubes (NACNTs), VACNTs increase the oxygen reduction reaction taking place at the cathode by a factor of two. In addition, vertical alignment also increases the power density up to 2.5 times with respect to NACNTs. VACNTs grown at the anode can further improve the cell performance by increasing the electrode surface area and thus the electron transfer between bacteria and the electrode. The maximum power density obtained using VACNTs was 14 mW/m2 and 160 mV output voltage.

11 páginas,6 figuras, 1 tabla., Bacteria and Archaea of the air–water surface microlayer (neuston) and plankton from three high mountain lakes (Limnological Observatory of the Pyrenees, Spain) were analysed by 16S rRNA gene 454 pyrosequencing (V6 region) in two dates with different atmospheric aerosol loading conditions: (1) under a Saharan dust plume driven by southern winds; and (2) under northern winds with oceanic influence. In general, bacterial communities were richer than archaea, with estimated total richness of c. 2500 OTUs for Bacteria and c. 900 OTUs for Archaea equivalent to a sequencing effort of c. 250 000 and c. 20 000 sequences, respectively. The dominant bacterial OTU was affiliated to Actinobacteria. Archaea were one to two orders of magnitude less abundant than bacteria but were more evenly distributed. Apparently, Bacteroidetes and Thaumarchaeota sequences were preferentially found at the neuston, but no consistent pattern in either total microbial abundance or richness was found in any sample. However, we observed more marked changes in microbial relative abundances between neuston and plankton in the dust-influenced scenario. Higher community dissimilarities between neuston and plankton were also found during the Saharan dust episode, and such differences were higher for Bacteria than for Archaea. Nonetheless, relatively few (< 0.05%) of the neuston sequences matched previously identified airborne microorganisms, and none became important in the dates analysed., This study was co-funded by the 7th Framework Programme (FP7) Marie Curie Fellowship (GenS FP7-MC-IOF- 219811) and a fellowship ‘Juan de la Cierva’ from the Ministry of Spanish Office of Science and Innovation (MICINN) to M.V.-C. and supported by grants PIRENA CGL2009-13318 and CONSOLIDER GRACCIE CSD2007-00067 from the MICINN, AERBAC-2 178/2010 from the Ministerio de Medio Ambiente-Red de Parques Nacionales to EOC and the Gordon and Betty Moore Foundation.

The ecological significance of the marine bacterial populations distinguishable by flow cytometry on the basis of the fluorescence (FL) of their nucleic acid (NA) content and proxies of cell size (such as side scatter, SSC) remains largely unknown. Some studies have suggested that cells with high NA (HNA) content and high SSC (HS) represent the active members of the community, while the low NA (LNA) cells are inactive members of the same phylogenetic groups. But group-specific activity measurements and phylogenetic assignment after cell sorting have suggested this is not be the case, particularly in open-ocean communities. To test the extent to which the different NA subgroups are similar, and consequently the extent to which they likely have similar ecological and biogeochemical roles in the environment, we analysed the phylogenetic composition of three populations after cell sorting [high NA-high SC (HNA-HS), high NA-low SC (HNA-LS), low NA (LNA)] by 454 pyrosequencing in two contrasting periods of the year in NW Mediterranean coastal waters (BBMO, Blanes Bay Microbial Observatory) where these three populations have recurrent seasonal patterns. Statistical analyses showed that summer and winter samples were significantly different and, importantly, the sorted populations within a sample were composed of different taxa. The majority of taxa were associated with one NA fraction only, and the degree of overlap (i.e. OTUs present simultaneously in 2 fractions) between HNA and LNA and between summer and winter communities was very small. Rhodobacterales, SAR116 and Bacteroidetes contributed primarily to the HNA fraction, whereas other groups such as SAR11 and SAR86 contributed largely to the LNA fractions. Gammaproteobacteria other than SAR86 showed less preference for one particular NA fraction. An increase in diversity was observed from the LNA to the HNA-HS fraction for both sample dates. Our results suggest that, in Blanes Bay, flow cytometric signatures of natural communities track their phylogenetic composition.