Influencia de bioestimulantes sobre la accesibilidad microbiana de Hidrocarburos Aromáticos Policíclicos

Los hidrocarburos aromáticos policíclicos (HAPs) son contaminantes orgánicos clasificados como tóxicos, mutagénicos y cancerígenos que normalmente se encuentran acumulados en suelos que han sido contaminados con petróleo, creosota o alquitrán de hulla. Los HAPs con 4 o menos anillos de benceno pueden ser utilizados como fuente de carbono y de energía por un amplio rango de microorganismos, mientras que la degradación de HAPs de alto peso molecular (más de 4 anillos) es normalmente a través de cometabolismo. No obstante, la baja solubilidad en agua de todos ellos y su gran capacidad de adsorción limitan su accesibilidad microbiana y restringen su biodegradación en suelos. En esta tesis se plantean varias estrategias para mejorar la accesibilidad microbiana de los HAPs en diferentes escenarios basándonos en tratamientos de bioestimulación. Para cada escenario se utilizó un bioestimulante diferente porque para que se produzca una biorremediación exitosa, cada técnica o método de mejora ambiental se tiene que adaptar a las necesidades del emplazamiento o acuífero a descontaminar.El presente trabajo se ha realizado en el marco del proyecto CGL2007-64199 del Plan Nacional de I +D (CYCIT), dentro del Programa Nacional de Formación de Personal Investigador (FPI).Peer Reviewe

Influence of the sunflower rhizosphere on the biodegradation of PAHs in soil

Reduced bioavailability to soil microorganisms is probably the most limiting factor in the bioremediation of polycyclic aromatic hydrocarbons PAH-polluted soils. We used sunflowers planted in pots containing soil to determine the influence of the rhizosphere on the ability of soil microbiota to reduce PAH levels. The concentration of total PAHs decreased by 93% in 90 days when the contaminated soil was cultivated with sunflowers, representing an improvement of 16% compared to contaminated soil without plants. This greater extent of PAH degradation was consistent with the positive effect of the rhizosphere in selectively stimulating the growth of PAH-degrading populations. Molecular analysis revealed that the increase in the number of degraders was accompanied by a dramatic shift in the structure of the bacterial soil community favoring groups with a well-known PAH-degrading capacity, such as Sphingomonas (α-Proteobacteria), Commamonas and Oxalobacteria (β-Proteobacteria), and Xhanthomonas (γ-Proteobacteria). Other groups that were promoted for which degrading activity has not been reported included Methylophyllus (β-Proteobacteria) and the recently described phyla Acidobacteria and Gemmatimonadetes. We also conducted mineralization experiments on creosote-polluted soil in the presence and absence of sunflower root exudates to advance our understanding of the ability of these exudates to serve as bio-stimulants in the degradation of PAHs. By conducting greenhouse and mineralization experiments, we separated the chemical impact of the root exudates from any root surface phenomena, as sorption of contaminants to the roots, indicating that sunflower root exudates have the potential to increase the degradation of xenobiotics due to its influence on the soil microorganisms, where sunflower root exudates act improving the availability of the contaminant to be degraded. We characterized the sunflower exudates in vitro to determine the total organic carbon (TOC) and its chemical composition. Our results indicate that the rhizosphere promotes the degradation of PAHs by increasing the biodegradation of the pollutants and the number and diversity of PAH degraders. We propose that the biostimulation exerted by the plants is based on the chemical composition of the exudates.Support for this research was provided by the Spanish Ministry of the Economy and Competitiveness (grants CGL2007-64199, CGL2010-22068-C02-01 and CGL2010-22068-C02-02).Peer Reviewe

The effect of humic acids on biodegradation of polycyclic aromatic hydrocarbons depends on the exposure regime

Binding of polycyclic aromatic hydrocarbons (PAHs) to dissolved organic matter (DOM) can reduce the freely dissolved concentration, increase apparent solubility or enhance diffusive mass transfer. To study the effects of DOM on biodegradation, we used phenanthrene and pyrene as model PAHs, soil humic acids as model DOM and a soil Mycobacterium strain as a representative degrader organism. Humic acids enhanced the biodegradation of pyrene when present as solid crystals but not when initially dissolved or provided by partitioning from a polymer. Synchronous fluorescence spectrophotometry, scintillation counting and a microscale diffusion technique were applied in order to determine the kinetics of dissolution and diffusive mass transfer of pyrene. We suggest that humic acids can enhance or inhibit biodegradation as a result of the balance of two opposite effects, namely, solubilization of the chemicals on the one hand and inhibition of cell adhesion to the pollutant source on the other.Support for this research was provided by the Spanish Ministry of Economy and Competitiveness (grants CGL2007-64199 and CGL2010-22068-C02-01), the FPI Program (M.C. Tejeda-Agredano), Junta de Andalucía (PAI RNM 312) and the European Commission (MODELPROBE, no. 213161).Peer Reviewe

New biological and physicochemical approaches to improve bioremediation performance in PAH-polluted soils

Bioavailability is one of the most important factors in determining the success or failure in the bioremediation of soils polluted polycyclic aromatic hydrocarbons (PAHs). Current bioremediation technology faces this situation by periodical substrate homogenization and, when it is cost-effective and technically feasible, by the addition of chemical or biological surfactants. We have prospected, at laboratory scale, two new mobilization approaches, one based on chemotactic bacteria and another focused on electrokinetics, to further bioremediation performance. Chemotaxis. Bacterial chemotaxis enables motile cells to move along chemical gradients and to swim towards optimal places for biodegradation. Chemotactic bacteria can therefore constitute in bioremediation projects a useful vector for relevant catabolic activities and/or nutrients. In well-controlled column systems, we assessed the influence of the chemoeffectors naphthalene, salicylate, fumarate, and acetate on deposition of chemotactic, naphthalene-degrading Pseudomonas putida G7 and its chemotaxis-negative mutant P. putida G7.C1 (pHG1000) in selected porous environments (sand, forest soil, and clay aggregates). Our data showed that the presence of the chemoeffectors in the pore water decreased deposition of strain G7 (but not of strain G7.C1) by 50% in sand-filled columns. Similar effects were observed for the other chemoeffectors. Deposition, however, depended on the chemoeffector?s chemical structure, its interaction with the column packing material, and concomitantly its pore-water concentration. We suggest that chemotactic sensing, combined with changed swimming modes, is likely to influence the deposition of bacteria in the subsurface. Electroosmosis. The integration of bioremediation and electrokinetics (electrobioremediation) for the treatment of hydrophobic organic soil-contaminants has recently been addressed as a relevant innovative step in soil remediation. However, to our knowledge, there have been limited attempts (documented) to connect these two technologies with remediation of HOCs and, more specifically, PAHs. We employed soils with different texture (clay soil and loamy sand) containing a mixture of PAHs present in creosote, and inoculation with a representative soil bacterium (Mycobacterium gilvum VM552) able to degrade fluorene, phenanthrene, fluoranthene, pyrene, anthracene and benzo[a]pyrene. Two different modes of treatment were prospected: 1) inducing in soil the simultaneous occurrence of biodegradation and electroosmosis in the presence of a biodegradable surfactant, and 2) treating sequentially the soils with electrokinetics and bioremediation. Losses of PAH due to biodegradation and electroosmosis (induced by a continuous electric field) were significantly higher than in control cells that contained the surfactant but no biological activity or no current. The use of periodical changes in polarity and current pulses increased in the removal of PAHs.Peer Reviewe

Effect of interface fertilization on biodegradation of polycyclic aromatic hydrocarbons present in nonaqueous-phase liquids

The main goal of this study wasto use an oleophilic biostimulant (S-200) to target possible nutritional limitations for biodegradation of polycyclic aromatic hydrocarbons (PAHs) at the interface between nonaqueous-phase liquids (NAPLs) and the water phase. Biodegradation of PAHs present in fuel-containing NAPLs was slow and followed zero-order kinetics, indicating bioavailability restrictions. The biostimulant enhanced the biodegradation, producing logistic (S-shaped) kinetics and 10fold increases in the rate of mineralization of phenanthrene, fluoranthene, and pyrene. Chemical analysis of residual fuel oil also evidenced an enhanced biodegradation of the alkyl- PAHs and n-alkanes. The enhancement was not the result of an increase in the rate of partitioning of PAHs into the aqueous phase, nor was it caused by the compensation of any nutritional deficiency in the medium. We suggest that biodegradation of PAH by bacteria attached to NAPLs can be limited by nutrient availability due to the simultaneous consumption of NAPL components, but this limitation can be overcome by interface fertilization.Peer Reviewe

Is it possible to increase bioavailability but not environmental risk of PAHs in bioremediation?

The current poor predictability of end points associated with the bioremediation of polycyclic aromatic hydrocarbons (PAHs) is a large limitation when evaluating its viability for treating contaminated soils and sediments. However, we have seen a wide range of innovations in recent years, such as an the improved use of surfactants, the chemotactic mobilization of bacterial inoculants, the selective biostimulation at pollutant interfaces, rhizoremediation and electrobioremediation, which increase the bioavailability of PAHs but do not necessarily increase the risk to the environment. The integration of these strategies into practical remediation protocols would be beneficial to the bioremediation industry, as well as improve the quality of the environment.Peer reviewe

Strategies to increase bioavailability and uptake of hydrocarbons

12 páginas.-- 50 referenciasThe biodegradation of hydrocarbons in the environment is often slow due to restricted bioavailability. Research performed during the last 20 years has shown possible pathways to increase the bioavailability of hydrocarbons without necessarily increasing the risk to the environment. Pollutant solubilization through (bio)surfactants, microbial transport, and attachment to pollutant interfaces can increase bioavailability, which translates into an enhancement of biodegradation rates. These strategies can not only be integrated into optimized bioremediation protocols that lead to lower decontamination endpoints in soils and sediments but also help to improve biodegradation in other environmental contexts, such as wastewater treatment and natural attenuation.This study was supported by the Spanish Ministry of Science and Innovation (CGL2013-44554-R and CGL2016-77497-R), the Andalusian Government (RNM 2337), and the European Commission (LIFE15 ENV/IT/000396).Peer reviewe

Impact of dissolved organic matter on bacterial tactic motility, attachment, and transport

8 páginas.-- 4 figuras.-- 1 tabla.-- 47 referencias.-- Supporting Information: Figures showing quantitative and qualitative tactic response to DOM and amino acids, transport of sonicated cells with high-DOM exudates, and the effect of sorbed humic acids on bacterial transport; Table showing chemical composition of DOM solutions; and Videos showing bacterial cell motility with and without exudates. This material is available free of charge via the Internet at http://pubs.acs.org/doi/suppl/10.1021/es5056484© 2015 American Chemical Society. Bacterial dispersal is a key driver of the ecology of microbial contaminant degradation in soils. This work investigated the role of dissolved organic matter (DOM) in the motility, attachment, and transport of the soil bacterium Pseudomonas putida G7 in saturated porous media. The study is based on the hypothesis that DOM quality is critical to triggering tactic motility and, consequently, affects bacterial transport and dispersal. Sunflower root exudates, humic acids (HA), and the synthetic oleophilic fertilizer S-200 were used as representatives of fresh, weathered, and artificially processed DOM with high nitrogen and phosphorus contents, respectively. We studied DOM levels of 16-130 mg L-1, which are representative of DOM concentrations typically found in agricultural soil pore water. In contrast to its responses to HA and S-200, strain G7 exhibited a tactic behavior toward root exudates, as quantified by chemotaxis assays and single-cell motility observations. All DOM types promoted bacterial transport through sand at high concentrations (∼130 mg L-1). At low DOM concentrations (∼16 mg L-1), the enhancement occurred only in the presence of sunflower root exudates, and this enhancement did not occur with G7 bacteria devoid of flagella. Our results suggest that tactic DOM effectors strongly influence bacterial transport and the interception probability of motile bacteria by collector surfaces.Experimental assistance from Jana Reichenbach and Birgit Würz (UFZ) is gratefully acknowledged. Support for this research was provided by the Spanish Ministry of Science and Innovation (Grants CGL2010-22068-C02-01 and CGL2013-44554-R), the Andalusian Government (RNM 2337), and the CSIC JAE Programme (C. Jimenez-Sanchez). This study also contributes to the research program Terrestrial Environment and the research topic ‘Chemicals in the Environment (CITE)’ of the Helmholtz Association.Peer Reviewe