Potential Impact of Biodegradable Surfactants on Foam-Based Microalgal Cultures

14 páginas.- 6 figuras.- 43 referenciasMicroalgae cultivation in liquid foams is a promising concept which requires the use of a surfactant as a foam stabilizing agent. The biodegradable character of a surfactant is a key aspect regarding its applicability in a liquid foam-bed photobioreactor (LF-PBR), since it might influence microalgal growth and the stability of the foam-based cultivation. In this work, the effects of the biodegradable surfactants bovine serum albumin (BSA), Saponin and Tween 20 on the whole microbial community of microalgal cultures (i.e., microalgal and bacterial populations) were studied. The three surfactants enhanced bacterial and microalgal growth in non-axenic microalgal cultures, but they differed in their efficiency to sustain bacterial growth. In this sense, Saponin was proven to enhance the growth of S. obliquus-associated bacteria in microalgae-free cultures, and to sustain it even when other nutrients were lacking, suggesting that Saponin can be used as an energy and nutrients source by these bacteria. The degradation and consumption of Saponin by S. obliquus-associated bacteria was also confirmed by the foaming capacity decrease in Saponin-added bacterial cultures. The biodegradable character of BSA, Saponin and Tween 20 reduces their suitability to be used in a LF-PBR since they would not be able to maintain stable foaming.This work was performed in the framework of EU MIRACLES project which received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 613588. The authors also acknowledge the funding received from Rensma, University of Huelva, for publishing open access.Peer reviewe

Behavioural Influences on Mineralization and Cometabolism of PAHs by Motile Bacteria in Membrane Bioreactors With Restricted Porosities

Poster presentado en the SETAC Europe 31st Annual Meeting from 2–6 May 2021 in Seville, Spain.The controlled dispersal of motile bacteria through contaminated soils is currently considered as one of the most promising aspects in bioremediation. The difficulty caused by the heterogeneous distribution of the pollutants and the degrading bacteria can be overcome by the use of different chemoefectors. These compounds provide the control over bacterial tactic motility, what results in an increase in the efficiency of the microorganisms dispersion and subsequently, enhanced biodegradation rates (Environ. Sci. Technol. 42: 1131-1137, 2008; Environ. Sci. Technol. 46: 6790-6797, 2012). The objective of this study was to evaluate the dispersal and biodegradation capacity through Mineralization tests with 14C-labelled naphthalene and cometabolism tests [by synchronous fluorescence spectrophotometry (Appl. Environ. Microbiol. 76 (13): 4430-4437; Sci. Total Environ. 717: 137210)] with pyrene by the chemotactic bacterium Pseudomonas putida G7 (cell dimensions: 1 μm x 3 μm). The experimental design consisted in a bioreactor system with two chambers separated by a membrane with specific pore sizes that restrict bacterial dispersal (Environ. Sci. Technol. 49: 14368-14375, 2015). Different chemoffectors (GABA and artificial root exudates) were used to modulate the motile bacterial behavior throught restricted porosities (5 μm). The initial results were promising. The transport of P. putida G7 through the membrane occurred at higher rates than the control for both chemoeffectors, thus enhancing biodegradation rates. The cometabolism process was evaluated by fluorescence spectrophotometry determinations, measuring the effect of P. putida G7 on the removal of aqueous- dissolved pyrene in the presence of the chemical effectors. Progress in this field will undoubtedly open up new possibilities for bioremediation processes in contaminated soils, improving the existing techniques for the treatment of poorly bioaccessible contaminants.N

Role of tactic response on the mobilization of motile bacteria through micrometer-sized pores

10 páginas.- 6 figuras.- 1 tabla.- referencias .- . Supplementary data Figures showing the FIB-SEM images of the membrane bioreactor experiments, the tactic response of Pseudomonas putida G7 under sonication conditions in transport assays and capillary test and bioreactor transport experiments with different concentrations of the chemoeffectors. Tables showing the experimental growth control with chemical effectors and bacterial accessibility to the different porous fractions of contaminated soil. Supplementary data to this article can be found online at: doi.org/10.1016/j.scitotenv.2022.154938A major cause of high bioremediation endpoints is the limited bioaccessibility to residual contaminants resting in soil pores with diameters close to the size exclusion limit of bacterial cells. Under nongrowing conditions and in the absence of hydraulic flow, we examined how the tactic behavior of motile, contaminant-degrading Pseudomonas putida G7 cells (2 × 1 μm) influenced passage through membranes with pores ranging in size from 1 μm to 12 μm. The bacteria were spontaneously retained by the membranes - even those with the largest pore size. However, the cells were mobilized through 5 μm and 12 μm pores after the application of an attractant (salicylate). Mobilization also occurred by attraction to the common root exudate constituents γ-aminobutyric acid and citrate and repellence (or negative taxis) to zero-valent iron nanoparticles. The observed pore size threshold for tactic mobilization (5 μm) and unaltered cell fluxes and effective cell diffusion against different chemoeffector strengths and concentrations suggest that there is a physical constraint on the gradient sensing mechanism at the pores that drives the tactic response. Our results indicate that chemically mediated, small-scale tactic reactions of motile bacteria may become relevant to enhance the bioaccessibility of the residual contaminants present in micrometer-sized soil pores.We would like to thank the Spanish Ministries of Economy and Competitiveness (CGL2016-77497-R) and Science and Innovation (BES-2017-079905 and PID2019-109700RB-C21) for supporting this workPeer reviewe

Chemoeffectors influence on the motile behavior and dispersion of pollutantdegrading bacteria in membrane bioreactors with restricted porosities.

Poster (4.04P.9) presentado en SETAC SciCon SETAC Europe 30th Annual Meeting, Open Science for Enhanced Global Environmental Protection 3–7 May 2020 Dublin, IrelandThe controlled dispersal of motile bacteria through contaminated soils is currently considered as one of the most promising aspects in bioremediation. The difficulty caused by the heterogeneous distribution of the pollutants and the degrading bacteria can be overcome by the use of different chemoefectors. These compounds provide the control over bacterial tactic motility, what results in an increase in the efficiency of the microorganisms dispersion and subsequently, enhanced biodegradation rates (Environ. Sci. Technol. 42: 1131-1137, 2008; Environ. Sci. Technol. 46: 6790-6797, 2012). The objetive of this study was to evaluate the dispersal capacity of the chemotactic bacterium Pseudomonas putida G7 (cell dimensions: 1 µm x 3 µm) through bioreactors assays. The innovative experimental design consisted in a bioreactor system with two chambers separated by a membrane with specific pore sizes that restrict the bacterial dispersal (Environ. Sci. Technol. 49: 14368-14375, 2015). Different chemoffectors (salicylate, glucose, zero-valent iron nanoparticles [Environ. Pollut. 213:438-445, 2016] and the root exudates components:¿-aminobutyric acid (GABA) and citrate) were used to modulate the motile bacterial behavior throught restricted porosities (1 µm to 12 µm). The initial results were promising. The transport of P. putida G7 through the membrane occurred at higher rates than the control for the majority of chemoeffectors. Progress in this field will undoubtedly open up new possibilities for bioremediation processes in contaminated soils, improving the existing techniques for the treatment of poorly bioaccessible contaminants

Impact of bacterial motility on biosorption and cometabolism of pyrene in a porous medium

8 páginas.- 6 figuras.- 40 referenciasThe risks of pollution by polycyclic aromatic hydrocarbons (PAHs) may increase in bioremediated soils as a result of the formation of toxic byproducts and the mobilization of pollutants associated to suspended colloids. In this study, we used the motile and chemotactic bacterium Pseudomonas putida G7 as an experimental model for examining the potential role of bacterial motility in the cometabolism and biosorption of pyrene in a porous medium. For this purpose, we conducted batch and column transport experiments with 14C-labelled pyrene loaded on silicone O-rings, which acted as a passive dosing system. In the batch experiments, we observed concentrations of the 14C-pyrene equivalents well above the equilibrium concentration observed in abiotic controls. This mobilization was attributed to biosorption and cometabolism processes occurring in parallel. HPLC quantification revealed pyrene concentrations well below the 14C-based quantifications by liquid scintillation, indicating pyrene transformation into water-soluble polar metabolites. The results from transport experiments in sand columns revealed that cometabolic-active, motile cells were capable of accessing a distant source of sorbed pyrene. Using the same experimental system, we also determined that salicylate-mobilized cells, inhibited for pyrene cometabolism, but mobilized due to their tactic behavior, were able to sorb the compound and mobilize it by biosorption. Our results indicate that motile bacteria active in bioremediation may contribute, through cometabolism and biosorption, to the risk associated to pollutant mobilization in soils. This research could be the starting point for the development of more efficient, low-risk bioremediation strategies of poorly bioavailable contaminants in soils. © 2020 Elsevier B.V.We thank the Spanish Ministry of Economy, Industry and Competitiveness (CGL2016-77497-R), the Andalusian Government (RNM 2337), and the European Commission (LIFE15 ENV/IT/000396). Joaquim Vila is a Serra Húnter Fellow (Generalitat de Catalunya).Peer reviewe

Root-mediated bacterial accessibility and cometabolism of pyrene in soil

13 páginas.-- 6 figuras.- 1 tablas.- 43 referencias.- Supplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2020.143408Partial transformation of pollutants and mobilization of the produced metabolites may contribute significantly to the risks resulting from biological treatment of soils polluted by hydrophobic chemicals such as polycyclic aromatic hydrocarbons (PAHs). Pyrene, a four-ringed PAH, was selected here as a model pollutant to study the effects of sunflower plants on the bacterial accessibility and cometabolism of this pollutant when located at a spatially distant source within soil. We compared the transformation of passively dosed 14C-labeled pyrene in soil slurries and planted pots that were inoculated with the bacterium Pseudomonas putida G7. This bacterium combines flagellar cell motility with the ability to cometabolically transform pyrene. Cometabolism of this PAH occurred immediately in the inoculated and shaken soil slurries, where the bacteria had full access to the passive dosing devices (silicone O-rings). Root exudates did not enhance the survival of P. putida G7 cells in soil slurries, but doubled their transport in column tests. In greenhouse-incubated soil pots with the same pyrene sources instead located centimeters from the soil surface, the inoculated bacteria transformed 14C-labeled pyrene only when the pots were planted with sunflowers. Bacterial inoculation caused mobilization of 14C-labeled pyrene metabolites into the leachates of the planted pots at concentrations of approximately 1 mg L−1, ten times greater than the water solubility of the parent compound. This mobilization resulted in a doubled specific root uptake rate of 14C-labeled pyrene equivalents and a significantly decreased root-to-fruit transfer rate. Our results show that the plants facilitated bacterial access to the distant pollutant source, possibly by increasing bacterial dispersal in the soil; this increased bacterial access was associated with cometabolism, which contributed to the risks of biodegradation. © 2020 Elsevier B.V.We thank the Spanish Ministries of Economy and Competitiveness ( CGL2016-77497-R ) and Science and Innovation ( PID2019-109700RB-C21 ) for supporting this work.Peer reviewe

Pyrene co-metabolism in soil by Pseudomonas putida G7 and metabolite uptake and distribution by sunflower crops.

Poster (f4.04P.8) presentado en SETAC SciCon SETAC Europe 30th Annual Meeting, Open Science for Enhanced Global Environmental Protection 3–7 May 2020 Dublin, IrelandPolycyclic aromatic hydrocarbons (PAHs) are a recalcitrant group of contaminants, known to be highly persistent in the environment. Most of these compounds, such as pyrene (PYR), are persistent pollutants in the soil. Actually, motility and dispersal are key ecological drivers that allow bacteria to move toward places of bene¿cial environmental conditions and to maintain significant ecosystem functions. Few studies have been carried out on the use of plant growth regulators and their influence on the removal of PAHs from the soil. However, no studies have been conducted on the effect of 14C on crops with sunflowers and its effect on PYR removal efficiency in the soil. The present study aims to investigate the effects of the simultaneous application of 14C PYR by passive dosing (O-rings) and inoculation with Pseudomonas putida G7 on the enhancement of PYR removal in the presence of sunflowers. The experiment was carried out in a greenhouse at 23 ± 1 ºC. The treatments included planted soil with the simultaneous application of bacteria and pyrene (T1), planted soil with pyrene (T2) and unplanted soil with pyrene and bacteria (T3). Planted soil (C1) and planted soil with bacteria (C2) were included as positive controls. Furthermore, in order to identify the metabolites formed during the experiment a preliminary study under laboratory conditions was achieved. Samples of leachates, soil and plant were obtained at different times from cultivation until harvest for the investigation of uptake, transport, and accumulation of the microbially-processed PYR in sunflowers. The results showed that planted soil with simultaneous application of pyrene and bacteria treatments enhanced the efficiency of pyrene transformation. The roots presented the highest levels of uptake and greatest bioconcentration factors. GC¿MS analyses of the extracts from the preliminary studies revealed the presence of 3 metabolites due to pyrene cometabolism by P. putida G7. From the data acquired, we suggest that the combined phytoremediation and bioaugmentation can be a suitable alternative for reducing risks during remediation of PAH-contaminated soils

Potential Risk From Biological Treatment of Soils Contaminated by Organic Chemicals: Root-Mediated Bacterial Accessibility and Cometabolism of Pyrene

Poster presentado en the SETAC Europe 31st Annual Meeting from 2–6 May 2021 in Seville, Spain.Healthy and resilient soil ecosystems are essential to help mitigate and adapt to climate change, but pressure on soil systems is increasing. Enhancing natural attenuation processes is a sustainable alternative for the restoration of soils contaminated by organic chemicals represented by PAHs and co-occurring compounds. The flow of hydrophobic contaminants to degradative microbial communities in soil can be significantly affected by microbial positioning along the contaminant paths, which may result in enhanced or diminished biodegradation rates. In this study, the flagellated bacterium Pseudomonas putida G7, which degrades pyrene by cometabolism, was cultivated and prepared differently for soil slurry experiments, metabolite analyses and greenhouse experiments. Additionally, we integrated passive dosing with 14C-labeled pyrene, inoculation of motile bacteria into soil and a complete sunflower (Helianthus annuus L.) ontogenic cycle to evaluate a new scenario related to pollutant transformation and risk in soil. A preliminary evaluation of possible risks to human and ecosystems were also done. Our results showed that the plants facilitated bacterial access to the distant pollutant source, possibly by increasing bacterial dispersal in the soil; this increased bacterial access was associated with cometabolism. Cometabolism of this PAH occurred immediately in the inoculated and shaken soil slurries, where the bacteria had full access to the passive dosing devices (silicone O-rings). Furthermore, the resulting metabolites were not only mobilized into the soils leachates but also taken up by the plants, accumulating in the roots at significantly higher proportions in inoculated samples than in uninoculated controls and acting differently on their way to the fruits. This new, proof-ofconcept scenario successfully showed that bacterial cometabolism may contribute to the environmental risk from PAHs in soil by improving pollutant mobilization and uptake by plants. These results are relevant in the bioremediation field because they show how inoculated bacteria can be mobilized by plants to reach distant pollutant sources and how partial pollutant transformation may generate further issues. Our results may also contribute to other pollution management sectors, such as wastewater treatment and prospective risk evaluation of agrochemicals, where rhizosphere microorganisms play a relevant roleN

Risk reductions during pyrene biotransformation and mobilization in a model plant-bacteria-biochar system

10 páginas.- 2 figuras.- 4 tablas.- referenicas.-Supplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2023.161600.The productive application of motile microorganisms for degrading hydrophobic contaminants in soil is one of the most promising processes in modern remediation due to its sustainability and low cost. However, the incomplete biodegradation of the contaminants and the formation of the intermediary metabolites in the process may increase the toxicity in soil during bioremediation, and motile inoculants may mobilize the pollutants through biosorption. Therefore, controlling these factors should be a fundamental part of soil remediation approaches. The aim of this study was to evaluate the sources of risk associated with the cometabolism-based transformation of 14C-labeled pyrene by inoculated Pseudomonas putida G7 and identify ways to minimize risk. Our model scenario examined the increase in bioaccessibility to a distant source of contamination facilitated by sunflower (Helianthus annuus L.) roots. A biochar trap for mobilized pollutant metabolites and bacteria has also been employed. The experimental design consisted of pots filled with a layer of sand with 14C-labeled pyrene (88 mg kg−1) as a contamination focus located several centimeters from the inoculation point. Half of the pots included a biochar layer at the bottom. The pots were incubated in a greenhouse with sunflower plants and P. putida G7 bacteria. Pots with sunflower plants showed a higher biodegradation of pyrene, its mobilization as metabolites through the percolate and the roots, and bacterial mobilization toward the source of contamination, also resulting in increased pyrene transformation. In addition, the biochar layer efficiently reduced the concentrations of pyrene metabolites collected in the leachates. Therefore, the combination of plants, motile bacteria and biochar safely reduced the risk caused by the biological transformation of pyrene.We would like to thank the Spanish Ministries of Economy and Competitiveness (CGL2016-77497-R) and Science and Innovation (PID2019-109700RB-C21 and PRIMA project PCI2020-111967) for supporting this work. We also acknowledge the European Union's Horizon 2020 research and innovation program (Marie Sklodowska-Curie grant agreement no. 895340; BIOTAC project)Peer reviewe