Sequential solvent extraction as a tool for evaluating hydrocarbons speciation in soil after electrochemical treatment.

Soluble and total extractable concentrations used for predicting contaminants' environmental fate may lead to uncertainties due to the lack of understanding of soil-contaminants interactions. The present study focuses on the influence of a controlled electric field on the distribution of polycyclic aromatic hydrocarbons in soil samples evaluated through a speciation scheme. Soil samples were spiked with 25,000 mg (hexadecane, phenanthrene, and pyrene 100:1:1 w/w) per kg of soil, and speciation of hydrocarbons was determined by employing a novel Sequential Solvent Extraction procedure, resulting in five fractions: soluble, pseudosoluble, desorbable, extractable, and sequestered. The distribution of hydrocarbons was then changed through the application of an electric field (72 h, 0.708 mA cm-2, 2.95 ±â€¯0.13 V cm-1), which modified the interactions in the soil-water interface. The electrochemical treatment significantly increased the pyrene soluble, desorbable and sequestered fractions by 340, 1.3 and 19-fold (p < 0.05); the hexadecane soluble fraction increased in 6-fold (p < 0.05) and the phenanthrene desorbable fraction increased in 1.3-fold (p < 0.05). The use of the speciation scheme proposed in this study provides a wider view of hydrocarbons distribution in soils, rather than using water-soluble or total extractable concentrations. Finally, this speciation scheme is proposed as a tool to evaluate the environmental fate of organic contaminants in soils.

Stable bioemulsifiers are produced by Acinetobacter bouvetii UAM25 growing in different carbon sources.

Acinetobacter species are identified as producing surface-active and emulsifying molecules known as bioemulsifiers. Production, characterization and stability of bioemulsifiers produced by Acinetobacter bouvetii UAM25 were studied. A. bouvetii UAM25 grew in three different carbon and energy sources: ethanol, a glycerol-hexadecane mixture and waste cooking oil in an airlift bioreactor, showing that bioemulsifier production was growth associated. The three purified bioemulsifiers were lipo-heteropolysaccharides of high molecular weight (4866 ± 533 and 462 ± 101 kDa). The best carbon source and energy for bioemulsifier production was wasted cooking oil, with a highest emulsifying capacity (76.2 ± 3.5 EU mg-1) as compared with ethanol (46.6 ± 7.1 EU mg-1) and the glycerol-hexadecane mixture (49.5 ± 4.2 EU mg-1). The three bioemulsifiers in our study displayed similar macromolecular structures, regardless of the nature (hydrophobic or hydrophilic) of the carbon and energy source. Bioemulsifiers did not decrease surface tension, but the emulsifying capacity of all of them was retained under extreme variation in salinity (0-50 g NaCl L-1), pH (3-10) and temperature (25-121 °C), indicative of remarkable stability. These findings contribute to understanding of the relationship between: production, physical properties, chemical composition and stability of bioemulsifiers for their potential applications in biotechnology, such as bioremediation of hydrocarbon-contaminated soil and water.

Polycyclic aromatic hydrocarbon-emulsifier protein produced by Aspergillus brasiliensis (niger) in an airlift bioreactor following an electrochemical pretreatment.

An emulsifier protein (EP) was produced and easily separated from oil-contaminated water as an economical substrate when Aspergillus brasiliensis, pretreated in a solid state culture with a controlled electric field, was used in an airlift bioreactor. The hydrocarbon-EP comprised 19.5% of the total protein, its purification enhanced the specific emulsifying activity (EA) seven times. The influence of operational conditions (pH and salt concentration) on the EA were assessed to characterise the emulsion stability. The EA was increased by 19% in alkaline environments (pH 7-11), but it was not affected by the presence of salt (0-35 g L-1). On the other hand, preheating the EP samples (60 °C) enhanced the EA by 2.5 times. Based on analysis of its EA, this EP can be applied as a bioremediation enhancer in contaminated soils.

Alterations in Aspergillus brasiliensis (niger) ATCC 9642 membranes associated to metabolism modifications during application of low-intensity electric current.

The effects of electric current on membranes associated with metabolism modifications in Aspergillus brasiliensis (niger) ATCC 9642 were studied. A 450-mL electrochemical cell with titanium ruthenium-oxide coated electrodes and packed with 15g of perlite, as inert support, was inoculated with A. brasiliensis spores and incubated in a solid inert-substrate culture (12 d; 30°C). Then, 4.5days after starting the culture, a current of 0.42mAcm-2 was applied for 24h. The application of low-intensity electric current increased the molecular oxygen consumption rate in the mitochondrial respiratory chain, resulting in high concentrations of reactive oxygen species, promoting high lipoperoxidation levels, according to measured malondialdehyde, and consequent alterations in membrane permeability explained the high n-hexadecane (HXD) degradation rates observed here (4.7-fold higher than cultures without current). Finally, cell differentiation and spore production were strongly stimulated. The study contributes to the understanding of the effect of current on the cell membrane and its association with HXD metabolism.

Fungal biocatalyst activated by an electric field: Improved mass transfer and non-specificity for hydrocarbon degradation in an airlift bioreactor.

The combination of biological and electrochemical techniques enhances the bioremediation efficiency of treating oil-contaminated water. In this study a non-growing fungal whole cell biocatalyst (BC; Aspergillus brasiliensis attached to perlite) pretreated with an electric field (EF), was used to degrade a hydrocarbon blend (hexadecane-phenanthrene-pyrene; 100:1:1w/w) in an airlift bioreactor (ALB). During hydrocarbon degradation, all mass transfer resistances (internal and external) and sorption capacity were experimentally quantified. Internal mass transfer resistances were evaluated through BC effectiveness factor analysis as a function of the Thiele modulus (using first order reaction kinetics, assuming a spherical BC, five particle diameters). External (interfacial) mass transfer resistances were evaluated by kLa determination. EF pretreatment during BC production promoted surface changes in BC and production of an emulsifier protein in the ALB. The BC surface modifications enhanced the affinity for hydrocarbons, improving hydrocarbon uptake by direct contact. The resulting emulsion was associated with decreased internal and external mass transfer resistances. EF pretreatment effects can be summarized as: a combined uptake mechanism (direct contact dominant followed by emulsified form dominant) diminishing mass transfer limitations, resulting in a non-specific hydrocarbon degradation in blend. The pretreated BC is a good applicant for oil-contaminated water remediation.

Enhanced hexadecane degradation and low biomass production by Aspergillus niger exposed to an electric current in a model system.

The effects of an electric current on growth and hexadecane (HXD) degradation by Aspergillus niger growth were determined. A 450-mL electrochemical cell with titanium ruthenium-oxide coated electrodes and packed with 15 g of perlite (inert biomass support) was inoculated with A. niger (2.0×10(7) spores (g of dry inert support)(-1)) and incubated for 12 days (30 °C; constant ventilation). 4.5 days after starting culture a current of 0.42 mA cm(-2) was applied for 24h. The current reduced (52±11%) growth of the culture as compared to that of a culture not exposed to current. However, HXD degradation was 96±1.4% after 8 days whereas it was 81±1.2% after 12 days in control cultures. Carbon balances of cultures not exposed to current suggested an assimilative metabolism, but a non-assimilative metabolism when the current was applied. This change can be related to an increase in total ATP content. The study contributes to the knowledge on the effects of current on the mycelial growth phase of A. niger, and suggests the possibility of manipulating the metabolism of this organism with electric current.

[Studies on the effects of carbon:nitrogen ratio, inoculum type and yeast extract addition on jasmonic acid production by Botryodiplodia theobromae Pat. strain RC1]. / Estudio del efecto de la relación carbono:nitrógeno, el tipo de inóculo y la adición de extracto de levadura en la producción de ácido jasmónico con Botryodiplodia theobromae Pat. cepa RC1.

Jasmonic acid is a native plant growth regulator produced by algae, microorganisms and higher plants. This regulator is involved in the activation of defence mechanisms against pathogens and wounding in plants. Studies concerning the effects of carbon: nitrogen ratio (C/Nr: 17, 35 and 70), type of inoculum (spores or mycelium) and the yeast extract addition in the media on jasmonic acid production by Botryodiplodia theobromae were evaluated. Jasmonic acid production was stimulated at the carbon: nitrogen ratio of 17. Jasmonic acid productivity was higher in the media inoculated with mycelium and in the media with yeast extract 1.7 and 1.3 times, respectively.

Biodegradation of high concentrations of hexadecane by Aspergillus niger in a solid-state system: kinetic analysis.

Solid-state microcosms were used to assess the influence of constant and variable C/N ratios on the biodegradation efficiency by Aspergillus niger at high hexadecane (HXD) concentrations (180-717 mg g-1). With a constant C/N ratio, 100% biodegradation (33-44% mineralization) was achieved after 15 days, at rates increasing as the HXD concentration increased. Biomass yields (YX/S) remained almost independent (approximately 0.77) of the carbon-source amount, while the specific growth rates (mu) decreased with increasing concentrations of HXD. With C/N ratios ranging from 29 to 115, complete degradation was only attained at 180 mg g-1, corresponding to 46% mineralization. YX/S diminished (approximately 0.50 units) as the C/N ratio increased. The highest values of mu (1.08 day-1) were obtained at low C/N values. Our results demonstrate that, under balanced nutritional conditions, high HXD concentrations can be completely degraded in solid-state microcosms, with a negligible (<10%) formation of by-products.

[A survey of temperature and pH effect on colonial growth of Botryodiplodia theobromae RC1]. / Efecto de la temperatura y el pH en el crecimiento superficial de Botryodiplodia theobromae RC1.

Study of fungal colonial growth is a basic method to examine their behaviour in different cultivation conditions. The influence of temperature and initial pH on growth radial velocity and growth density of Botryodiplodia theobromae RC1, was studied in order to show the growth characteristics of this fungus. Both temperature and culture medium influenced growth density, but radial velocity of growth was only affected by temperatures above 40 degrees C. In addition, initial pH of culture media did not affect either parameter.