RESUMEN
Lecanicillium lecanii, Verticillium chlamydosporium, V. fungicola var flavidum and Beauveria bassiana were evaluated on their growth with pure n-hexane, toluene and n-hexane:toluene 17:83 (v:v) mixture. Another set of treatments were conducted with colloidal chitin as additional carbon source. All the strains of Lecanicillium were able to grow using hydrocarbons with or without the addition of chitin, although the presence of hydrocarbons showed significant inhibition evidenced by measured biomass, radial growth and microscopic analyses. Degradation of n-hexane ranged within 43 and 62 % and it was higher than that with toluene. The strains L460, L157 and L2149, which presented the highest growth, were further selected for determinations of hydrocarbon consumptions in microcosms. Strain L157 showed the highest consumption of n-hexane (55.6 %) and toluene (52.9 %) as sole carbon source and it also displayed activities of endochitinases, N-acetylhexosaminidase and production of hydrophobins class I and II.
Asunto(s)
Amidohidrolasas/biosíntesis , Ascomicetos/crecimiento & desarrollo , Quitinasas/biosíntesis , Proteínas Fúngicas/biosíntesis , Hexanos/metabolismo , Tolueno/metabolismoRESUMEN
Fungal biofilters have been recently studied as an alternative to the bacterial systems for the elimination of hydrophobic volatile organic compounds (VOC). Fungi foster reduced transport limitation of hydrophobic VOCs due to their hydrophobic surface and extended gas exchange area associated to the hyphal growth. Nevertheless, one of their principal drawbacks is their slow growth, which is critical in the start-up of fungal biofilters. This work compares the use of different carbon sources (glycerol, 1-hexanol, wheat bran, and n-hexane) to reduce the start-up period and sustain high n-hexane elimination capacities (EC) in biofilters inoculated with Fusarium solani. Four parallel experiments were performed with the different media and the EC, the n-hexane partition coefficient, the biomass production and the specific consumption rate were evaluated. Biofilters were operated with a residence time of 1.3 min and an inlet n-hexane load of 325 g m(-3) (reactor) h(-1). The time to attain maximum EC once gaseous n-hexane was fed was reduced in the three experiments with alternate substrates, as compared to the 36 days needed with the control where only n-hexane was added. The shortest adaptation period was 7 days when wheat bran was initially used obtaining a maximum EC of 160 g m(-3) (reactor) h(-1) and a critical load of 55 g m(-3) (reactor) h(-1). The results were also consistent with the pressure drop, the amount of biomass produced and its affinity for the gaseous n-hexane, as represented by its partition coefficient.
Asunto(s)
Biodegradación Ambiental , Reactores Biológicos , Hongos/metabolismo , Hexanos/aislamiento & purificación , Compuestos Orgánicos Volátiles/aislamiento & purificación , Fibras de la Dieta/metabolismo , Glicerol/metabolismo , Hexanos/metabolismo , Hexanoles/metabolismo , Interacciones Hidrofóbicas e Hidrofílicas , Compuestos Orgánicos Volátiles/metabolismoRESUMEN
2,5-Hexanedione (2,5-HD) is the most important metabolite of n-hexane and methyl ethyl ketone in human urine. Urinary 2,5-HD is used as a biomarker for biological monitoring of workers exposed to n-hexane. A simple method using headspace solid-phase microextraction (HS-SPME) and gas chromatography (GC) equipped with a flame-ionization detector (FID) was developed. The parameters that affect the HS-SPME-GC-FID process were optimized (i.e., fiber coating, sample volume, adsorption and heating time, salt addition, and extraction temperature). The assay presented linearity in the range of 0.075 to 20.0 mg/L, precision (coefficient of variation < 7.0%), and detection limit of 0.025 mg/L for 2,5-HD in urine. The method was successfully applied to the analysis of 2,5-HD in urine samples from eight workers occupationally exposed to n-hexane in shoemaker's glue.
Asunto(s)
Adhesivos/metabolismo , Cromatografía de Gases , Monitoreo del Ambiente/métodos , Hexanos/metabolismo , Hexanonas/orina , Exposición Profesional , Microextracción en Fase Sólida , Biomarcadores/orina , Biotransformación , Calibración , Cromatografía de Gases/normas , Monitoreo del Ambiente/normas , Ionización de Llama , Humanos , Reproducibilidad de los Resultados , Zapatos , Microextracción en Fase Sólida/normasRESUMEN
The removal of volatile organic compounds (VOC) in biofilters packed with organic filter beds, such as peat moss (PM) and pine sawdust (PS), frequently presents drawbacks associated to the collapse of internal structures affecting the long-term operation. Poly(ethylene ether carbonate) (PEEC) groups grafted to these organic carriers cross linked with 4,4'-methylenebis(phenylisocyanate) (MDI) permitted fiber aggregation into specific shapes and with excellent hexane sorption performance. Modified peat moss (IPM) showed very favorable characteristics for rapid microbial development. Water-holding capacity in addition to hexane adsorption almost equal to the dry samples was obtained. Pilot scale hexane biofiltration experiments were performed with the composites after inoculation with the filamentous fungus Fusarium solani. During the operation of the biofilter under non-aseptic conditions, the addition of bacterial antibiotics did not have a relevant effect on hexane removal, confirming the role of fungi in the uptake of hexane and that bacterial growth was intrinsically limited by an adequate performance of the composites. IPM biofilter had a start-up period of 8-13 days with concurrent CO(2) production of approximately 90 g m(-3) h(-1) at day 11. The final pressure drop after 70 days of operation was 5.3 mmH(2)O m(-1) reactor. For modified pine sawdust (IPS) packed biofilter, 5 days were required to develop an EC of about 100 g m(-3) h(-1) with an inlet hexane load of approximately 190 g m(-3) h(-1). Under similar conditions, 12-17 days were required to observe a significant start-up in the reference perlite biofilter to reach gradually an EC of approximately 100 g m(-3) h(-1) at day 32. Under typical biofiltration conditions, the physical-chemical properties of the modified supports maintained a minimum water activity (a(w)) of 0.925 and a pH between 4 and 5.5, which allowed the preferential fungal development and limited bacterial growth.
Asunto(s)
Contaminantes Atmosféricos/aislamiento & purificación , Contaminantes Atmosféricos/metabolismo , Fusarium/metabolismo , Hexanos/aislamiento & purificación , Polietilenos/química , Microbiología del Suelo , Ultrafiltración/métodos , Madera/microbiología , Gases/aislamiento & purificación , Gases/metabolismo , Hexanos/metabolismo , Proyectos Piloto , Ultrafiltración/instrumentaciónRESUMEN
Biofiltration of hydrophobic volatile pollutants is intrinsically limited by poor transfer of the pollutants from the gaseous to the liquid biotic phase, where biodegradation occurs. This study was conducted to evaluate the potential of silicone oil for enhancing the transport and subsequent biodegradation of hexane by the fungus Fusarium solani in various bioreactor configurations. Silicone oil was first selected among various solvents for its biocompatibility, nonbiodegradability, and good partitioning properties toward hexane. In batch tests, the use of silicone oil improved hexane specific biodegradation by approximately 60%. Subsequent biodegradation experiments were conducted in stirred-tank (1.5 L) and packed-bed (2.5 L) bioreactors fed with a constant gaseous hexane load of 180 g x m(-3)(reactor) x h(-1) and operated for 12 and 40 days, respectively. In the stirred reactors, the maximum hexane elimination capacity (EC) increased from 50 g x m(-3)(reactor) x h(-1) (removal efficiency, RE of 28%) in the control not supplied with silicone oil to 120 g x m(-3)(reactor) x h(-1) in the biphasic system (67% RE). In the packed-bed bioreactors, the maximum EC ranged from 110 (50% RE) to 180 g x m(-3)(reactor) x h(-1) (> 90% RE) in the control and two-liquid-phase systems, respectively. These results represent, to the best of our knowledge, the first reported case of fungi use in a two-liquid-phase bioreactor and the highest hexane removal capacities so far reported in biofilters.
Asunto(s)
Reactores Biológicos , Fusarium/metabolismo , Gases/metabolismo , Hexanos/metabolismo , Biodegradación Ambiental , Microscopía Electrónica de Rastreo , SolventesRESUMEN
Candida antarctica lipase fraction B (CAL-B) showed substrate specificity in the synthesis of esters in hexane involving reactions of short-chain acids having linear (acetic and butyric acids) and branched chain (isovaleric acid) structures, an unsaturated (tiglic acid) fatty acid, and phenylacetic acid with n-butanol and geraniol. The variation in the conversion to the esters was ca. 10%. Similar results were observed in a study of the alcohol specificity of the enzyme for esterification of acetic and butyric acids with four alcohols: n-butyl, isopentyl, 2-phenylethyl, and geraniol. Enantioselectivity of CAL-B in hexane with a range of chiral alpha-substituted or beta-substituted carboxylic acids and n-butyl alcohol was analyzed. The results show that CAL-B can be employed as a robust biocatalyst in esterification reactions due to the high conversions obtained in the synthesis of short-chain flavor esters in an organic solvent, although this enzyme exhibited modest enantioselectivity with chiral short-chain carboxylic acids.
Asunto(s)
Biotecnología/métodos , Candida/enzimología , Ésteres/metabolismo , Aromatizantes/metabolismo , Lipasa/metabolismo , Perfumes/metabolismo , 1-Butanol/metabolismo , Acetatos/metabolismo , Monoterpenos Acíclicos , Butiratos/metabolismo , Ácidos Carboxílicos/metabolismo , Crotonatos/metabolismo , Esterificación , Hemiterpenos , Hexanos/metabolismo , Ácidos Pentanoicos/metabolismo , Pentanoles/metabolismo , Fenilacetatos/metabolismo , Alcohol Feniletílico/metabolismo , Estereoisomerismo , Especificidad por Sustrato , Terpenos/metabolismoRESUMEN
Lipase (Glycerol ester hydrolase EC 3.1.1.3.) from a Brazilian strain of Fusarium solani FSI has been investigated. The effect of different carbon sources and trace elements added to basal medium was observed with the aim of improving enzyme production. Lipase specific activity was highest (0.45 U mg(-1)) for sesame oil. When this medium was supplemented with trace elements using olive oil, corn oil and sesame oil the lipase specific activity increased to 0.86, 1.89 and 1.64 U mg(-1), respectively, after 96 h cultivation without any considerable biomass increase. The Km of this lipase using pNPP (p-nitrophenylpalmitate) as substrate, was 1.8 mM with a Vmax of 1.7 micromol min(-1) mg protein(-1). Lipase activity increased in the presence of increasing concentrations of hexane and toluene. In contrast, incubation of this enzyme with water-soluble solvents decreased its activity after 10% concentration (v/v) of the solvent. The lipase activity was stable below 35 degrees C but above this temperature activity losses were observed.