Over 3.7 million people are in high risk of coastal flooding and live within 1 mile of high tide in the US alone. The Atlantic coast is one of the most vulnerable areas due to its low elevation, large population, and economic importance (Bray, et. al, 2016). Coastal municipalities in the region of Southeast Florida, such as the cities of Miami, Miami Beach, Fort Lauderdale, etc., are at especial risk from coastal flooding related to sea level rise. The US National Climate Assessment has named Miami, Florida as the economically most vulnerable city impacted by this sea level rise in the world (Melillo et. al, 2014). Virtually all coastal communities in Southeast Florida are now experiencing increased incidents of coastal tidal flooding and coastal storm flooding related to sea level rise. This has led to a variety of responses by coastal communities in how to address this issue. In the case of the City of Miami Beach, the city has [CS1] come up with an ambitious but expensive plan to help combat the increased urban coastal flooding that is now occurring multiple times a year. They invested over 500 million dollars into replacing the increasingly less-effective gravity-based drainage system with a pump-based system (Bray, et. al, 2016). With these influences, we hypothesized that microbial communities would significantly differ between three years (2014-2016) and that the potential pathogens would increase over the past years . Genetic analyses of the 16S rRNA V4 region yielded a total of 77,346 unique bacterial OTUs from a total of 96 samples collected monthly for three years from 2014-2016. The most abundant OTU within the whole sample set was New.ReferenceOTU407 or Arcobacter in the Campylobacter family with an overall abundance of 0.008232535481%.The second most abundant organism in the sample set was Bacillus, or OTUNew.CleanUp.ReferenceOTU121132, with an overall abundance of .007797807097%. Bacillusmay cause many more foodborne illness than is known and one main reason that there is not more reported cases is because people do not seek medical attention (FDA 2012). The remaining pathogens except for Serratia, Pleisomonas, and Cronobacter were all with an abundance over .001%, with Salmonella, Yersinia,andListeria not being identified at all within the data set. By showing that genetic signatures for this bacterium, especially Arcobacter,was present in more than half of the samples stresses the importance of better understanding of the microbial population within South Florida waters and how to prevent or reduce future outbreaks by making sure the water is treated correctly before use, and to better identify potential exposure sources in water.

The loss of biodiversity is affecting all ecosystems on Earth, one of the greatest threats to biodiversity being climate change. Forests have been highlighted for the potential to mitigate climate change by storing carbon above- and belowground in soils. In this thesis, I studied the effects of tree diversity on carbon cycling in subtropical Chinese forests. I aimed to explore the mechanisms behind tree diversity effects on carbon cycling by focusing on microbial-based processes and the consequences of tree diversity-induced spatial heterogeneity. First, my colleagues and I tested the effects of tree diversity on litterfall spatial patterns and the consequences for litter decomposition and quantified the importance of microbial community in decomposition processes. Second, we explored the effects of tree diversity on relationships between soil microbial facets and soil microbial functions. Third, we tested the effects of tree diversity on soil microbial biomass and carbon concentrations, and their mediation by biotic and abiotic conditions. Finally, we explored the consequences of diversifying forests for re-/afforestation initiatives and plantations to reduce atmospheric carbon levels, and the benefits of diversity for mitigating the effects of climate change on ecosystems and human well-being. We highlighted the positive effects of tree diversity on tree productivity. By increasing the amount and diversity of litterfall, tree diversity increased litter decomposition and subsequently the assimilation of tree products into the forest soils. Our investigation has shown the key role of microbial communities for forests carbon dynamics by carrying out litter decomposition, soil heterotrophic respiration, and soil carbon stabilization. Most notably, tree diversity effects on soil microbial respiration were mainly mediated by soil microbial biomass rather than soil microbial community taxonomic or functional diversity. The effects of tree diversity on microbial biomass were mediated by biotic and abiotic conditions. Taken together, we revealed the importance of considering space to understand biodiversity-ecosystem functioning relationships. Finally, we argued that tree diversity is a promising avenue to maximize the potential of re-/afforestation projects to mitigate increasing atmospheric carbon. Moreover, we highlighted that diversifying forests in re-/afforestation initiatives can help to reduce climate change effects on ecosystems: first, by increasing resistance and resilience to extreme climatic events, and second, by buffering microclimatic conditions in natural and urban areas. My investigation highlighted that tree diversity effects on ecosystem functioning could be explained by both mass and diversity effects on higher trophic levels and their functions. In addition, I showed the key role of tree diversity-induced spatial heterogeneity and the need to consider space and time in further research. Moreover, these results need to be combined with practitioner constraints to enable feasible restoration projects.:Summary table Bibliographic information .................................................................................... I ~ XV Main body ......................................................................................................... 1 ~ 212 Supplementary materials ..................................................................................... i ~ xv Scientific supplementary materials ............................................................. -1- ~ - 154- Table of Contents Table of figures .......................................................................................................... XI Table of scientific supplementary materials ............................................................. XIII Glossary ................................................................................................................... XV Introduction ................................................................................................................. 3 Chapter I - Tree diversity effects on litter decomposition are mediated by litterfall and microbial processes .................................................................................................. 35 Transition I - II ........................................................................................................... 67 Chapter II - Tree diversity and soil chemical properties drive the linkages between soil microbial community and ecosystem functioning................................................ 71 Transition II - III ....................................................................................................... 107 Chapter III - Abiotic and biotic drivers of scale-dependent tree trait effects on soil microbial biomass and soil carbon concentration ................................................... 111 Transition III - IV ..................................................................................................... 155 Chapter IV – Diverse forests are cool: promoting diverse forests to mitigate carbon emissions and climate change ............................................................................... 159 General discussion ................................................................................................. 173 Abstract .................................................................................................................. 195 General acknowledgments ..................................................................................... 209 Supplementary materials ..............................................................................................i

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Reindeer appear to have strong positive effects on plant productivity and nutrient cycling in strongly nutrient-limited ecosystems. While the direct effects of grazing on vegetation composition have been intensively studied, much less is known about the indirect effect of grazing on plant-soil interactions. This thesis investigated the indirect effects of ungulate grazing on arctic plant communities via soil nutrient availability and plant nutrient uptake. At high density, the deposition of dung alone increased plant productivity both in nutrient rich and nutrient poor tundra habitats without causing major changes in soil possesses. Plant community responses to dung addition was slow, with a delay of at least some years. By contrast, a 15N-urea tracer study revealed that nutrients from reindeer urine could be rapidly incorporated into arctic plant tissues. Soil and microbial N pools only sequestered small proportions of the tracer. This thesis therefore suggests a strong effect of dung and urine on plant productivity by directly providing nutrient-rich resources, rather than by stimulating soil microbial activities, N mineralization and ultimately increasing soil nutrient availability. Further, defoliation alone did not induce compensatory growth, but resulted in plants with higher nutrient contents. This grazing-induced increase in plant quality could drive the high N cycling in arctic secondary grasslands by providing litter of a better quality to the belowground system and thus increase organic matter decomposition and enhance soil nutrient availability. Finally, a 15N natural abundance study revealed that intense reindeer grazing influences how plants are taking up their nutrients and thus decreased plant N partitioning among coexisting plant species. Taken together these results demonstrate the central role of dung and urine and grazing-induced changes in plant quality for plant productivity. Soil nutrient concentrations alone do not reveal nutrient availability for plants since reindeer have a strong influence on how plants are taking up their nutrients. This thesis highlights that both direct and indirect effects of reindeer grazing are strong determinants of tundra ecosystem functioning. Therefore, their complex influence on the aboveground and belowground linkages should be integrated in future work on tundra ecosystem N dynamic.

Dans un contexte de réchauffement climatique, la fonction puits de carbone des tourbières à sphaignes est susceptible d’être altérée en raison d’une modification des interactions sphaignes-microorganismes, responsables de l’accumulation de carbone. L’objectif de cette thèse a été (1) d’identifier les interactions chimiques entre les polyphénols des sphaignes et les communautés microbiennes des sphaignes et (2) d’évaluer l’impact du réchauffement climatique sur ces relations.Un dispositif expérimental (Open Top Chambers) simulant in situ une hausse modérée des températures (+ 1°C) a été installé sur la tourbière de Frasne (25). La hausse des températures a provoqué une modification du réseau alimentaire microbien avec l’augmentation de la biomasse des bactéries et une baisse importante (-70%) de la biomasse des prédateurs (amibes à thèque). Le réchauffement climatique a également induit une baisse de la production de polyphénols, diminuant ainsi leur effet inhibiteur sur les microorganismes. En parallèle à cette baisse, une hausse des activités enzymatiques phénoloxydases a également été enregistrée. Le réchauffement a ainsi modifié les relations polyphénols – phénoloxydases, deux éléments essentiels du cycle du carbone des tourbières.Les différents changements induits par le réchauffement climatique (polyphénols, phénoloxydases, réseau trophique microbien) ont aussi conduit à une modification des relations « sphaignes-microorganismes » via une accélération potentielle du recyclage des nutriments, ce qui pourrait influencer sur le long terme le fonctionnement de l’écosystème tourbière. / Carbon stocks of Sphagnum-peatlands are likely to be altered by climate warming due to important changes in “Sphagnum-microorganisms” relationships which are responsible for carbon sequestration. The objectives of the thesis are (1) to identify the chemical interactions between Sphagnum-polyphenols and Sphagnum associated microbial communities and (2) to understand the impact of warming on these relationships.An experimental design using Open-Top-Chambers (OTC) was used to simulate an increase of air temperatures (+1°C) on a peatland situated in Jura Mountains (Frasne, 25). Temperature increase induced a modification of the microbial food web with an increase of the biomass of bacteria and a strong decrease of the biomass of top-predators (-70%), i.e. testate amoebae. Warming also induced a decrease of Sphagnum-polyphenols, diminishing their inhibitory effect on microbial communities. In parallel, an increase of phenoloxidase enzymatic activities was recorded in OTC. Climate warming thus modified polyphenol-phenoloxidase interplay, two crucial components of carbon cycle in peatlands. Warming effects on the different components – i.e. polyphenols, phenoloxidases, microbial food web – induced a modification of Sphagnum-microbial communities interplay, favoring carbon and nutrient recycling, which could alter peatland functioning in long-term.

Certaines pratiques agricoles telles que l’épandage de produits résiduaires organiques (PRO) ou l’irrigation des sols peuvent être à l’origine de l’introduction de bactéries pathogènes de l’Homme dans les sols. Le sol joue alors un rôle central dans la dissémination de ces bactéries pathogènes dans les différents compartiments de l’environnement et peut contaminer les matières premières végétales, les animaux d’élevage mais également les ressources en eau. Le risque sanitaire associé à la dissémination de ces bactéries pathogènes doit être évalué afin de limiter le développement de maladies infectieuses. Dans ce contexte, l’incidence et le potentiel de survie de bactéries pathogènes a été étudié dans un large ensemble de sols provenant du territoire français (Réseau de Mesure de la Qualité des Sols : RMQS). Ce travail a pour objectif général d’identifier les facteurs biotiques et abiotiques des sols qui déterminent l’incidence et la survie de d’un pathogène strict, Listeria monocytogenes, et d’un pathogène opportuniste, Enterococcus faecalis, dans ces matrices environnementales Pour ceci, 2 approches ont été adoptées : la première approche a visé à mettre au point des systèmes de détection de PCR quantitative spécifiques pour ces deux espèces bactériennes afin de détecter et quantifier ces 2 bactéries dans un ensemble de 1200 ADN de sols présentant des paramètres pédoclimatiques contrastés. L. monocytogenes n’est pas détectée dans les ADN de sols avec la méthode moléculaire développée, dont le seuil de détection est d’environ 104 bactéries par gramme de sol. La détection moléculaire d’E. faecalis a été biaisée par un problème de contamination des ADN extraits. Après extraction de nouveaux ADN sur 150 échantillons de sol, E. faecalis a été détecté en faible quantité dans 5 des 150 sols testés (4% des sols) à des concentrations d’environ 102 bactéries par gramme de sol. Dans une deuxième approche, la survie de L. monocytogenes et d’E. faecalis a été suivie dans un ensemble de 100 sols caractérisés par des paramètres pédoclimatiques variables. Des microcosmes de sols ont été inoculés et la survie bactérienne a été évaluée par des méthodes culturales classiques. L. monocytogenes survit à long terme dans un plus grand nombre de sols qu’E. faecalis. Les sols favorables à la survie à long terme sont majoritairement (44%) les mêmes pour les 2 bactéries. Les sols sableux présentant un pH acide sont défavorables à la survie des 2 bactéries. Cependant des différences sont observées quant aux paramètres physico-chimiques des sols qui déterminent la survie de ces 2 bactéries. Ainsi, la survie de L. monocytogenes est corrélée positivement au taux de saturation en cations basiques, à la capacité d’échange cationique et à la concentration en calcium pour le court terme et à la teneur en argile pour le long terme. En revanche, pour E. faecalis, une corrélation négative avec la teneur en calcium total est trouvée pour la survie à court terme alors que la survie à long terme est négativement corrélée à la concentration en phosphore assimilable. Un effet inhibiteur de la microflore des sols a été mis en évidence sur la survie de L. monocytogenes et E. faecalis : il est statistiquement significatif pour les sols présentant un pH supérieur à 7 pour les 2 pathogènes. Les résultats obtenus vont permettre de modéliser la survie de ces pathogènes dans les sols en fonction de paramètres pédo-climatiques et donc à terme de mieux gérer les épandages de PRO en fonction des types de sols pour limiter la persistance de pathogènes dans les sols. / Soil contamination by bacterial pathogens can occur through manure, sewage sludge spreading or irrigation using waste water treatment plants effluents. Agricultural soils may act as reservoirs for these pathogens, play a significant role in their dissemination, leading to the potential contamination of food and water resources. Health risk associated with the occurrence of pathogens in environmental matrices has to be thoroughly evaluated. In this context, the objectives of this work were: i) to determine the prevalence of two pathogenic bacterial species (Listeria monocytogenes and Enterococcus faecalis) in a large collection of French soils originated from a systematic soil survey of the territory, called RMQS (16x16 km grid), ii) to determine major biotic and abiotic parameters driving the survival of bacterial pathogens in soils. Two approaches were used to reach these objectives: i) the prevalence of the two pathogens was monitored in 1200 soils using specific molecular detection tools (real time PCR using TaqMan probe detection system) and ii) the survival of the 2 pathogens, inoculated in soil microcosms, was determined over a 84 days incubation period under laboratory conditions, on a subset of 100 soils from the RMQS survey, using classical microbiological methods. L. monocytogenes was not detected in the set of 1200 soils (with a detection limit estimated to be 104 bacteria per gram of soil) using the molecular detection method, while E. faecalis was detected in approximately 4% of the soils tested (on a smaller set of 150 RMQS soils). The two bacterial pathogens were able to survive in the majority of soil, although L. monocytogenes survived in a greater number of soils. Soils where both pathogens survived represented 44% of soils. The survival of both pathogens is strongly impaired in sandy acidic soils. However, textural and chemical parameters driving survival of the two pathogens differed: L. monocytogenes survival is increased in soils with higher BCSR (basic cation saturation ration) and CEC (cation exchange capacity). L. monocytogenes long-term survival is favored by higher soil clay content. E. faecalis survival is impaired in soils with high total Ca content (calcareous soils). Soil microflora inhibits survival of both pathogens especially in soil with alcaline pH’s. The results of our study will allow implementing survival models for these two pathogens. Such data is invaluable for a better and safer managment of soil manuring using various organic residues.

Um método baseado na extração de rRNA, seguido de RT-PCR rRNA 16S, clonagem e ARDRA foi otimizado e validado para a identificação das bactérias ativas em biofilmes. O método foi analisado primeiro com consórcios artificiais de três organismos. As etapas de clonagem e RT não causaram variações importantes na composição destes consórcios, do contrário da etapa de PCR, onde foi necessária a redução de 30 para 10 ciclos para limitar a distorção da proporção de templates. A análise de biofilmes reais indicou que clones dominantes podem ser identificados com o critério de ocorrência de >2% na biblioteca, mas que a reprodutibilidade de análises ainda é insatisfatória, possivelmente devido a fatores como a micro heterogeneidade espacial do biofilme, viés na reação de PCR e formação de mais de um clone de ARDRA por organismo. O armazenamento do biofilme a -20 °C por 2 meses não levou à alterações expressivas em sua composição. O perfil de clones detectado com o kit (Mo Bio) de extração de RNA foi muito diferente do perfil detectado com o método otimizado neste trabalho. / A method based on extraction of rRNA, followed by RT-PCR of 16S rRNA, cloning and ARDRA was optimized and validated for identification of bacteria active in biofilms. The method was first tested with artificial three-membered consortia. Cloning and RT did not lead to significant changes in the composition of the artificial consortia, but a reduction in cycle number in the PCR reaction from 30 to 10 was necessary for limiting the distortion in the proportion of amplicons relative to that of the templates. Analysis of real biofilms revealed that clones from active organisms occurred in frequencies >2% in the clone library, but reproducibility of analysis was unsatisfactory, probably due to factors such as the spatial heterogeneity of colonization of biofilms by microbes, PCR bias and more than one ARDRA clone per organism. Storage of biofilm samples at -20 °C for 2 months did not lead to important changes in composition. Very different clone profiles were obtained in the analysis of the same biofilm sample with the optimized method and with a kit (Mo Bio) for extraction of RNA.

Ce travail a permis d’étudier la dynamique saisonnière des communautés microbiennes (cytométrie en flux et MiSeq ADNr16S) d'un étang sursalé thalassohalin. Malgré les variations de salinité (15,5 à 32 %), un core microbiome hautement stable (97,2± 2,1%) et dominé par Haloquadratum (40,3 à 57,4%) et Salinibacter (4,9 à 21,8%) a été décrit. De plus, des populations halotolérantes, capables de croitre rapidement, ont été détectées durant les épisodes de dilution des eaux. Dans un contexte physico-chimique contraignant où la biodégradation des hydrocarbures (HC) reste controversée, une première étude a été réalisée afin de comprendre le devenir d’un pétrole et son effet sur les communautés microbiennes actives de saumures proches de la saturation en sels (31%). Après biostimulation de ces communautés par l’ajout de matière organique labile et d'une température favorable (40°C), des phytolyptes actifs appartenant aux genres Haloarcula, Halobacterium et Halorubrum ont été détectés dans les microcosmes présentant de la biodégradation (12,8%) après 30 jours. Face aux limitations des processus d'autoépuration en contexte naturel (température plus faible), plusieurs approches de biostimulation testées (i.e. fertilisation minérale –NS ou organique –DS ; dilution) ont permis de forts taux d'atténuation des HC aliphatiques (97,8% et 54,5%) dans des saumures diluées (27,7 à 14%) et fertilisées (-DS et -NS). Dans ces mêmes microcosmes, des phylotypes actifs majoritaires appartenant aux genres Marinobacter et à la famille des Flavobacteriaceae (dont Psychroflexus) ont été détectés (MiSeq ADNr16S). L'opérabilité de ces traitements mériterait d'être testée à une plus large échelle. / This work performed on a thalassohaline hypersaline lake firstly considered seasonal dynamics of microbial communities (flow cytometry and MiSeq on 16S rRNA). Despite salinity fluctuations (15.5-32 %), a microbiome core highly stable at the genus level (97.2 ± 2.1 %) and dominated by Haloquadratum (40.3-57.4 %) and Salinibacter (4.9-21.8 %) was described. Interestingly, some halotolerant phylotypes exhibited rapid growths during dilutions episodes. In a controversial context concerning high salinity effects on hydrocarbons (HC) biodegradation, a study was conducted on close to salts-saturation brines (31 %) to gain insight into the fate of oil and it effects on active microbial communities after 15- and 30-days incubations. Significant oil biodegradation (12.8 %) was detected only after a 30-days incubation in LOM-amended microcosms while phylotypes belonging to Halobacteriaceae (Haloarcula, Halobacterium and Halorubrum) appeared as major active phylotypes. However, these low rates suggested that oil biodegradation should be lower under in situ conditions (lower temperature). Thus, among biostimulation approaches (mineral (-NS) or organic (-DS) amendments; dilution) used to improve self-cleaning processus, DS- or NS-amendments added to diluted brines (27.7 % to 14.0 %) allowed high attenuation rates of aliphatic HC with 97.8 % and 54.5 % respectively. Bacterial phylotypes belonging to Marinobacter and Flavobacteriaceae (e.g. Psychroflexus) were detected in NS- and DS-amended microcosms in which petroleum biodegradation occurred. This strategy will have, however, to be tested in other hypersaline systems (natural or industrial) in order to test its operational efficiency.

The meals from many oilseed crops contain biocidal chemicals that are known to inhibit the growth and activity of several soil pathogens, though little is known concerning impacts on whole soil microbial communities. We investigated the effect of oilseed meals (SMs) from both brassicaceous plants, including mustard and camelina, as well as non-brassicaceous plants, including jatropha and flax, on P. omnivora (the casual agent of cotton root rot) in Branyon clay soil (at 1 and 5% application rates). We also investigated the effect of SMs from camelina, jatropha, flax, and wheat straw on microbial communities in Weswood loam soil. We also used four types of isothiocyanates (ITCs) including allyl, butyl, phenyl, and benzyl ITC to test their effects on P. omnivora growth on potato dextrose agar (PDA), as well as on soil microbial communities in a microcosm study. Community qPCR assays were used to evaluate relative abundances of soil microbial populations. Soil microbial community composition was determined through tag-pyrosequencing using 454 GS FLX titanium technology, targeting ITS and 16S rRNA gene regions for fungal and bacterial communities, respectively. The results showed that all tested brassicaceous and jatropha SMs were able to inhibit P. omnivora sclerotial germination and hyphal growth, with mustard SM being the most effective. Flax didn't show any inhibitory effects on sclerotial germination. All tested ITCs inhibited P. omnivora OKAlf8 hyphal growth, and the level of inhibition varied with concentration and ITC type. Total soil fungal populations were reduced by ITC addition, and microbial community compositions were changed following SM and ITC application. These changes varied according to the type of SM or ITC added. Our results indicated that SMs of several brassicaceous species as well as jatropha may have potential for reducing cotton root rot as well as some other pathogens. Different SMs releasing varied ITCs may result in differential impacts on soil microorganisms including some pathogens.

Polycyclic aromatic hydrocarbons (PAHs) are pollutants of great concern due to their toxicity, ubiquitous distribution and environmental persistence. Generally, the PAHs are found as part of complex mixtures such as crude oil and derivatives, and mineral coal. Mismanagement during industrial operations, and accidental spills result in the contamination of wide areas with potential risk for the public health and negative impact in the local economy. Nowadays, there is a considerable interest in the use of biological procedures to clean up polluted environments because of their pollutant removal efficiency, feasibility and associated low cost. Bioremediation experiences are based on the ability that microorganisms (bacteria, algae and fungi) possess in degrading a wide range of pollutants, including PAHs containing from two to five aromatic rings. The microbial biodegradation of low molecular weight (LMW) PAHs has been extensively studied revealing a variety of bacteria capable to efficiently degrade these pollutants. The studies with high molecular weight (HMW) PAHs, more recalcitrant and with higher toxicity, indicate that in soil environments this compounds are generally degraded by members of the group Actinobacteria. However, little is known about HMW-PAH degradation in marine environments. Recent studies carried out with marine consortia and isolates have identified a few genera as PAHs degraders in sea waters, but no associations have been established between pyrene degradation and actinobacteria in such environments. Here, with the study of a pyrene microbial marine consortium, we provide the first evidence on the key role of actinobacteria in the removal of pyrene from polluted marine shorelines. Moreover, the detailed analysis of the community structure of the microbial consortium have revealed the presence of a bacterial strain not classifiable in the previously described genus, that have been isolated, thoroughly characterized and proposed as a type strain of a new genus and species. Bioremediation experiences do not always produce the desired results. PAHs are usually degraded until certain limit after which degradation is hardly observed. This phenomenon may be mainly caused by the low bioavailiability and limited concentration of nutrients. PAHs are usually found in non-aqueous phase liquids (NAPLs), which results in a slow partition of these components into the aqueous phase and their persistence in to the environment for long periods. In order to enhance microbial degradation and reduce the residual PAH concentration in polluted environments, we have conducted an experiment in which the effect of an oleophilic fertilizer has been evaluated. We also have targeted the possible nutritional deficiencies during bioremediation and have examined the biodegradation of PAHs and potential accumulation of partially oxidized metabolites, more available and toxic than their parent PAHs. Finally, we have evaluated the efficiency of sunflower rhizosphere in PAH removal from polluted soils that have undergone extensive remediation but still contain intolerable levels of pollutants. The results indicate that the sunflower rhizosphere enhance the removal of PAHs by promoting the selective growth of degradative bacteria, incrementing the bioaccesibility and possible favouring the degrading processes through specific mechanism associated with the composition of the roots exudates. These results represent a promising alternative for increasing bioremediation in a sustainable and cost-efficient manner. / Los hidrocarburos aromáticos policíclicos son un grupo de contaminantes que suscitan gran preocupación debido a su toxicidad, amplia distribución y persistencia en el medio ambiente. Generalmente, los HAPs se encuentran formando parte de mezclas complejas como crudos de petróleo, carbón mineral y derivados. La mala gestión durante las operaciones industriales, y los vertidos accidentales causan amplias áreas contaminadas que conllevan un importante riesgo para la salud pública junto con un impacto negativo en la economía local. Actualmente, hay un notable interés en el uso de procedimientos biológicos para descontaminar emplazamientos debido a la eficiencia en la eliminación, viabilidad y bajo coste asociado de estos métodos. Las experiencias de biorremediación se basan en la capacidad de los microorganismos (bacterias, algas y hongos) de degradar una amplia variedad de contaminantes, incluyendo HAPs. La degradación microbiana de HAPs de bajo peso molecular ha sido ampliamente estudiada revelando numerosas bacterias capaces de eliminar eficientemente estos compuestos. Los estudios realizados con HAPs de alto peso molecular, más recalcitrantes y con mayor toxicidad, han mostrado que en suelos la degradación de estos compuestos es principalmente llevada a cabo por miembros del grupo Actinobacteria. Sin embargo, se desconoce la degradación de HAPs de elevado peso molecular en ambientes marinos. Estudios recientes llevados a cabo en consorcios marinos han identificado algunos géneros degradadores de HAPs en agua de mar, pero no se han establecido asociaciones entre el pireno y actinobacterias. Aquí, con el estudio del consorcio marino degradador de pireno, nosotros proveemos la primera evidencia del papel de las actinobacterias en la eliminación del pireno de costas marinas. Además, el análisis de la estructura de la comunidad bacteriana nos reveló la presencia de una cepa no clasificable en los géneros previamente descritos, que fue aislada, profundamente caracterizada y propuesta como cepa tipo de un nuevo género y especie. Las experiencias de biorremediación no siempre producen los resultados deseados. A menudo. los HAPs son degradados hasta cierto límite tras el cual la degradación apenas es observada. Este fenómeno puede ser causado principalmente por la baja disponibilidad y limitación de nutrientes. Los HAPs generalmente se encuentran formando parte de fases líquidas no acuosas (FLNAs), lo que resulta en una lenta partición de estos compuestos hacia la fase acuosa y por tanto en una persistencia medioambiental. Con el fin de incrementar la degradación microbiana y reducir la concentración residual de los HAPs en ambientes contaminados, se realizó un experimento en el cual se evaluaba el efecto de un fertilizante oleofílico. También se examinaron las posibles deficiencias nutricionales y la acumulación de metabolitos parcialmente oxidados resultantes de la degradación, los cuales son más disponibles y tóxicos que sus parentales. Finalmente, hemos evaluado la eficiencia de la rizosfera de girasol en la eliminación de HAPs de suelos contaminados con HAPs que han sido sometidos a una extensiva remediación, pero que contienen niveles inaceptables de HAPs. Los resultados indican que la rizosfera de girasol aumentó la eliminación de HAPs promoviendo el crecimiento selectivo de bacterias degradadoras y favoreciendo los procesos de degradación a través de mecanismos asociados con la composición de los exudados. Los resultados representan por tanto una alternativa prometedora para potenciar la biorremediación de una manera sostenible y rentable.