Search

Syngas fermentation is a bioconversion technology of syngas/waste gas components to produce lowcarbon molecules. This technology is currently undergoing an intensive research and development phase.Acetogens (Clostridium, Eubacterium, Moorella) have been shown to ferment single carbon gases such as CO and CO2 plus H2 into chemicals (mainly acetate, ethanol, lactate or 2,3-BDO)through the acetyl-CoA pathway (Wood–Ljungdahl pathway). M. thermoacetica has great potential as microbial production platforms using syngas, because it has high growth and metabolism rates and low microbial contamination rates due to their high growth temperature. Here we describe a strategy for the gas fermentation using M. thermoacetica and a pressurized gas fermenter aimed to improve the overall reaction rate as well as the global yield of the process for the production of acetate. In a second fermentation stage, we investigated the use of acetate as main carbon source for the production of triacylglycerides (TAGs) using the oleaginous yeast Yarrowia lipolytica. This microorganism can accumulate in the form of lipid bodies, lipids of up to 60% wt/wt of their biomass. Fermentation conditions were studied at laboratory level to determine the most important parameters influencing lipid accumulation (pH, DO, C/N ratio) as well as alternative carbon sources to increase the yield of lipid production. For this purpose, not only batch and fed-batch fermentation processes but also continuous fermentations with cell recycle, fed with a diluted acetate solution,were carried out at lab scale using bench scale bioreactors of 1.5 L. The overall results showed that acetate produced from syngas can be used as promising, low-cost carbon source for growth and lipid production in Y. lipolytica, which can be further processed to obtain sustainable biofuels.

Rare earth elements (REE) are essential in the manufacture of high-technology goods. Tons of wastes containing REE are yearly accumulated; however, environmentally friendly recycling methods are poorly studied. The use of heterotrophic microorganisms could be particularly relevant in the bioleaching of wastes transforming insoluble REE-bearing compounds into more soluble forms which are directly and/or indirectly involved in their metabolism. In this study, bioleaching of rare earth elements from fluorescent phosphor powder in fluorescent tubes using Aspergillus niger CECT2807 was investigated. Bioleaching experiments were performed in batch cultures at 1% pulp density. The concentrations in solution reached 122 mg/l of Y, 8.50 mg/l of Eu, 0.95 mg/l of Ce, 0.40 mg/l of Tb and 1.11 mg/l of La, after 7 days. Then, REE precipitated due to the generation of oxalic acid by the fungus. The residues generated were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) and the lamp powder biotransformation was evidenced. Additionally, semicontinuous experiments were conducted and evidenced significant increase of REE dissolution rate in static conditions. The amount of extracted REE under static conditions reached 16.5 mg of Y and 0.75 mg of Eu per gram of fluorescent lamp powder.

The demand of rare earth elements (REE) has grown over the past decades due to their importance in high technology devices such as wind turbines, superconductors, rechargeable batteries, autocatalytic converters, magnets, or LED lighting. The development of clean mining processes is gaining interest and the biomining of REE is mainly focused on monazite using phosphate solubilizing microorganisms. The members of the genus Burkholderia can dissolve phosphorous from inorganic rocks. Furthermore, several species of Burkholderia are able to produce biosurfactants named rhamnolipids. Nevertheless, rhamnolipid interactions with REE have been poorly investigated. The aim of the present work is the study of the solubilization of monazite and the recovery of REE using the bacterium Burkholderia thailandensis, and the influence of the rhamnolipids produced by the bacteria in the REE mobilization. B. thailandensis grown in nutrient broth with 1% monazite (w/v) reached 8.3 mg·l−1 REE after 15 days. To produce rhamnolipids, B. thailandensis was grown in medium supplemented with 10% glycerol and the biosurfactants were extracted. The critical micelle concentration (CMC) was determined: 94.45 mg·l−1 for commercial rhamnolipids and 60.41 mg·l−1 for purified rhamnolipids. The maximum REE solubilization was obtained at CMC reaching 9.36 mg·l−1 with commercial rhamnolipids and 5.13 mg·l−1 with rhamnolipids produced by B. thailandensis E264.

Background: Manganese (Mn) oxides play a key role in the oxidation of recalcitrant organic carbon, including lignin (1), and have also emerged as a potential material in a wide range of technological applications, e. g, energy storage or catalysis. A transcriptomic study aimed to identify lignin-induced genes in the environmental model bacterium Pseudomonas putida KT2440 revealed pepA, encoding an animal-heme peroxidase-like enzyme homologous to certain Mn oxidases (2), as one of the main induced genes., Objectives: To characterise the mechanisms of secretion and action of PepA in P. putida KT2440., Methods: A collection of P. putida mutant strains was designed to unequivocally asses the function of pepA and that of the adjacent operon coding for a type-1 secretion system (T1SS). Liquid Chromatography coupled to tandem mass spectrometry (LC-MS/MS) was used to confirm localization and processing of the mature enzyme. Transmission (TEM) and scanning (SEM) electron microscopy techniques were applied to detect and characterise manganese oxides nanoparticles (MnOx NPs). Superoxide generation by PepA was tested by making use of a chemoluminescent probe., Results: This work shows that PepA is an extracellular heme-dependent enzyme that oxidizes Mn(II) by generating superoxide. A specific T1SS encoded adjacent to pepA is involved in PepA transport and processing of the mature form. A PepA-overproducer P. putida strain allowed the characterisation of the extracellular MnOx NPs generated. These results expand the knowledge on bacterial manganese oxidases and their potential role in lignin depolymerization, and broaden the biotechnological utilities of the model P. putida KT2440 bacterial chassis.

Rare earth elements (REE) are essential in the manufacture of high-technology goods. Tons of wastes containing REE are yearly accumulated; however, environmentally friendly recycling methods are poorly studied. The use of heterotrophic microorganisms could be particularly relevant in the bioleaching of wastes transforming insoluble REE-bearing compounds into more soluble forms which are directly and/or indirectly involved in their metabolism. In this study, bioleaching of rare earth elements from fluorescent phosphor powder in fluorescent tubes using Aspergillus niger CECT2807 was investigated. Bioleaching experiments were performed in batch cultures at 1% pulp density. The concentrations in solution reached 122 mg/l of Y, 8.50 mg/l of Eu, 0.95 mg/l of Ce, 0.40 mg/l of Tb and 1.11 mg/l of La, after 7 days. Then, REE precipitated due to the generation of oxalic acid by the fungus. The residues generated were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) and the lamp powder biotransformation was evidenced. Additionally, semicontinuous experiments were conducted and evidenced significant increase of REE dissolution rate in static conditions. The amount of extracted REE under static conditions reached 16.5 mg of Y and 0.75 mg of Eu per gram of fluorescent lamp powder., Universidad Complutense de Madrid, Ministerio de Ciencia e Innovación (España), Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

The demand of rare earth elements (REE) has grown over the past decades due to their importance in high technology devices such as wind turbines, superconductors, rechargeable batteries, autocatalytic converters, magnets, or LED lighting. The development of clean mining processes is gaining interest and the biomining of REE is mainly focused on monazite using phosphate solubilizing microorganisms. The members of the genus Burkholderia can dissolve phosphorous from inorganic rocks. Furthermore, several species of Burkholderia are able to produce biosurfactants named rhamnolipids. Nevertheless, rhamnolipid interactions with REE have been poorly investigated. The aim of the present work is the study of the solubilization of monazite and the recovery of REE using the bacterium Burkholderia thailandensis, and the influence of the rhamnolipids produced by the bacteria in the REE mobilization. B. thailandensis grown in nutrient broth with 1% monazite (w/v) reached 8.3 mg·l−1 REE after 15 days. To produce rhamnolipids, B. thailandensis was grown in medium supplemented with 10% glycerol and the biosurfactants were extracted. The critical micelle concentration (CMC) was determined: 94.45 mg·l−1 for commercial rhamnolipids and 60.41 mg·l−1 for purified rhamnolipids. The maximum REE solubilization was obtained at CMC reaching 9.36 mg·l−1 with commercial rhamnolipids and 5.13 mg·l−1 with rhamnolipids produced by B. thailandensis E264., Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

In order to better understand bacterial depolymerization of lignin, a new analytical approach was proposed using Pseudomonas putida KT2440 as delignifying bacterium and Escherichia coli as non-delignifying control. Two different types of lignins, technical Kraft lignin and synthetic dehydrogenopolymer (DHP), were submitted to a bioconversion kinetic study over 7 days. The concomitant analysis of the supernatant acid-precipitable lignin fraction and water-soluble extractives by high-performance size-exclusion chromatography (HPSEC) and gas chromatography – mass spectrometry (GC–MS) highlighted the specific action of P. putida towards these substrates, with the transitory formation of phenolic metabolites (dihydroferulic acid for Kraft lignins and dimers for DHP) and the prevention of Kraft lignin self-assemblying. In both cases lignin apparent depolymerization followed by repolymerization was observed. The analysis of the bacterial pellets indicated the time-increasing content of lignins associated to bacterial cells, which could account for the apparent structural changes observed with E. coli in the supernatant.

We have identified and characterized the AccS multidomain sensor kinase that mediates the activation of the AccR master regulator involved in carbon catabolite repression (CCR) of the anaerobic catabolism of aromatic compounds in Azoarcus sp. CIB. A truncated AccS protein that contains only the soluble C-terminal autokinase module (AccS′) accounts for the succinate-dependent CCR control. In vitro assays with purified AccS′ revealed its autophosphorylation, phosphotransfer from AccS′∼P to the Asp60 residue of AccR, and the phosphatase activity toward its phosphorylated response regulator, indicating that the equilibrium between the kinase and phosphatase activities of AccS′ may control the phosphorylation state of the AccR transcriptional regulator. Oxidized quinones, e.g., ubiquinone 0 and menadione, switched the AccS′ autokinase activity off, and three conserved Cys residues, which are not essential for catalysis, are involved in such inhibition. Thiol oxidation by quinones caused a change in the oligomeric state of the AccS′ dimer resulting in the formation of an inactive monomer. This thiol-based redox switch is tuned by the cellular energy state, which can change depending on the carbon source that the cells are using. This work expands the functional diversity of redox-sensitive sensor kinases, showing that they can control new bacterial processes such as CCR of the anaerobic catabolism of aromatic compounds. The AccSR two-component system is conserved in the genomes of some betaproteobacteria, where it might play a more general role in controlling the global metabolic state according to carbon availability.

Removal of aromatic compounds, which mostly derive from the polymer lignin, fossil fuel reservoirs, and industrial activities, is very important both for a balanced global carbon budget and to protect natural ecosystems and human health from the toxic effect of some of these environmental pollutants. Whereas the aerobic catabolism of aromatic compounds has been extensively studied for many decades, the anaerobic catabolism is a more recently discovered and so far poorly characterized microbial capacity despite the fact that anoxic conditions dominate in many natural habitats and contaminated sites. The anaerobic catabolism of aromatic compounds by some specialized bacteria becomes, thus, crucial for the biogeochemical cycles and for the sustainable development of the biosphere. Moreover, anaerobic degradation of aromatic compounds involves various intriguing biochemically unprecedented reactions that are also of great biotechnological potential as alternatives to the current synthesis processes and for the anaerobic valorization of aromatic compounds to produce biofuels, biopolymers, and commodity chemicals. In this chapter we summarize the major degradation pathways and the associated cellular responses when bacteria grow anaerobically in the presence of aromatic compounds. The unexplored potential and some biotechnological applications of the anaerobic catabolism of aromatic compounds are also discussed.

El objetivo de esta Tesis ha sido el estudio del fenómeno de represión catabólica en Sphingopyxis macrogolitabida TFA. Este tipo de regulación global está bien caracterizado en las principales bacterias modelo, pero su base molecular es totalmente desconocida dentro del orden Sphingomonadales, a pesar de que este grupo alberga varios géneros de bacterias con un relevante potencial en biorremediación. Dado que en TFA el metabolismo del compuesto aromático tetralina (1,2,3,4-tetrahidronaftaleno) está completamente caracterizado, se ha empleado esta ruta de degradación como referencia para el estudio de la base molecular que dirige el proceso de represión catabólica en presencia de otra fuente de carbono preferencial (ß-hidroxibutirato) en el medio. Durante el desarrollo de esta Tesis se ha realizado un análisis de la fisiología de la bacteria durante el crecimiento en condiciones de represión catabólica. Para ello, se ha estudiado la inducción de los genes de degradación de tetralina (sujetos a represión catabólica) in vivo y a lo largo del tiempo en distintas condiciones de disponibilidad de carbono. También se han identificado y analizado los cambios ocurridos en el proteoma de la bacteria como consecuencia del estímulo de represión catabólica. Con este fin, se han desarrollado experimentos de resolución del proteoma en geles bidimensionales y se han analizado las diferencias globales gracias al marcaje de las proteínas con fluoróforos (técnica 2D-DIGE) o con metionina radiactiva. El último tipo de estudio se desarrolló gracias a una estancia de investigación en el laboratorio del Prof. Michael Hecker (Greifswald, Alemania). Aparte del estudio fisiológico, se ha analizado la implicación de varios elementos específicos en el mecanismo de represión catabólica, elegidos bien por su expresión diferencial en condiciones de represión catabólica en los experimentos de proteómica o por su implicación en el mismo proceso de regulación global en otras bacterias. Así, se han c

Rhodococcus sp. strain TFB is a metabolic versatile bacterium able to grow on naphthalene as the only carbon and energy source. Applying proteomic, genetic and biochemical approaches, we propose in this paper that, at least, three coordinated but independently regulated set of genes are combined to degrade naphthalene in TFB. First, proteins involved in tetralin degradation are also induced by naphthalene and may carry out its conversion to salicylaldehyde. This is the only part of the naphthalene degradation pathway showing glucose catabolite repression. Second, a salicylaldehyde dehydrogenase activity that converts salicylaldehyde to salicylate is detected in naphthalene-grown cells but not in tetralin- or salicylate-grown cells. Finally, we describe the chromosomally located nag genes, encoding the gentisate pathway for salicylate conversion into fumarate and pyruvate, which are only induced by salicylate and not by naphthalene. This work shows how biodegradation pathways in Rhodococcus sp. strain TFB could be assembled using elements from different pathways mainly because of the laxity of the regulatory systems and the broad specificity of the catabolic enzymes.