PROIMI   05436
PLANTA PILOTO DE PROCESOS INDUSTRIALES MICROBIOLOGICOS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Actinomycetes involved in heavy metals bioremediation
Autor/es:
MANUEL SIÑERIZ LOUIS; MARTA A. POLTI; VIRGINIA H. ALBARRAC¨ªN; ERIKA KOTHE; MAR¨ªA J. AMOROSO; CARLOS M. ABATE
Lugar:
Penang, Malaysia
Reunión:
Simposio; Aquatic Sciences cum Enhacement of the Agro - industry; 2007
Institución organizadora:
Alexander von Humboldt Stiftung Foundation
Resumen:
Disposal of wastes from metal excavation and processing have concentrated the heavy metals to dangerous levels in some soils and sediments. Metal contamination of soil is especially problematic because of the strong adsorption of many metals to the surfaces of soil particles. Due to the difficulty of desorbing metal contaminants, some traditional remediation methods simply immobilize metals in contaminated soils, for example, by the addition of cement or chemical fixatives, by capping with asphalt, or by in-situ vitrification. Alternatively, soils are often isolated by excavation and confinement in hazardous waste facilities. Although rapid in effect, both of these options are expensive ($30¨C$300/ m3) and destroy the soil¡¯s future productivity. Some metals, such as calcium, cobalt, chromium copper, iron, magnesium are required nutrients and are essential. Others have no biological role (silver, aluminium, cadmium, lead, gold and mercury) and are nonessential. However these metals at higher concentrations are toxic to microorganisms.   The bioremediation is the use of microorganisms or microbial processes to degrade environmental contaminants, it may be an effective biotechnological approach to clean up these environments, and is an alternative to traditional landfilling or incineration. Bioremediation depends on the presence of the appropiate microorganisms in the correct amounts and conbinations and on the appropiate environmental conditions. Microorganisms already living in contaminated environments are often well-adapted to survival in the presence of existing contaminants and to the temperature, pH and oxidation-reduction potential of the site.   Lower cost and higher efficiency at low metal concentrations make bioremediation processes very attractive in comparison to physicochemical methods for heavy metal removal.. There are at least three types of microbial processes that can influence toxicity and transport of metals and radionuclides: biotransformation, biosorption and bioaccumulation, and degradation or synthesis of organic ligands that affect the solubility of the contaminants. Each offers the potential for bioremediation of metallic and radioactive contaminants in the environment.   The actinomycetes are a group of gram positive bacteria with a high G+C content, they are metabolicaly versatile with a highly active secondary metabolism and are found mainly in soil, being a substantial compound of the microflora. Actinomycetes produce many extracellular enzymes in soil. By decomposing complex mixtures of organic polymers with degrading exoenzymes and extracellular peroxidases, they are important to the recycling of nutrients associated with recalcitrant polymers. An advantage over Gram-negative soil bacteria is their ability to spread through relatively dry soil via hyphal growth and to survive adverse conditions by formation of durable exospores.   The aim of this work is to present actinomycete strains as potential useful tools to perform bioremediation processes in environments polluted with heavy metals (cadmium, chromium and copper).   Forty-six actinomycete strains were isolated from two polluted sites (a former uranium mine, Wismut, Germany and R¨ªo Hondo, Tucum¨¢n, Argentina) and one pristine site (Ushuaia Bay, Argentina). By primary qualitative screening assays the isolated Streptomyces sp. F4 strain was selected because of cadmium resistance and characterized physiologically and taxonomically; it grew up to 7.5% NaCl, until 100 ¦Ìg/ml lysozyme and at a pH range from 6 to 10. 16S rDNA sequence analysis showed that Streptomyces sp. F4 was very close to Streptomyces tendae. On culture medium with 8 mg L-1 Cd, 80% inhibition was observed after 8 days of growth. The maximum specific biosorption was 37.3 mg Cd/g cell after 7 days of growth. The highest Cd concentration was found into the cell wall, (41.2%). The exopolysaccharide layer contained only 7.4%, while the cytosol 39.4% of Cd. On the ribosomes and membrane fraction, 12 % were found. This localization was verified by transmition electron microscopy; where cells of Streptomyces sp. F4 showed a cytoplasm with dark granulate appearance.   Forty-one actinomycetes isolated from El Cadillal (EC), copper filter plant (CFP) and sugar cane palnt (SCP) (Tucum¨¢n Argentina) were used to study qualitative and semi-quantitative screening of chromium (VI) resistance. Twenty percent of the isolates from EC and 14% of isolates from CFP were able to grow at 13 mM of Cr (VI). All isolates SCP could grow up to Cr (VI) concentration of 17 mM. EC, CFP and SCP strains were able to remove 24%, 30% and more than 40% of Cr (VI), respectively. The highest and lowest Cr (VI) specific removal values were 75.5 mg g-1 cell by M3 (CFP), and 1.5 mg g-1 cell by C35 (EC) strains. Eleven Cr (VI) resistant strains were characterized and identified as species of the genera Streptomyces (10) and Amycolatopsis (1).   Fifty actinomycetes were isolated from copper contaminated (CFP) and non-contaminated area (EC) (Tucum¨¢n, Argentina). Primary qualitative screening assays showed that 100% of the isolated microorganisms of the contaminated area were resistant up to 80mg L-1 of CuSO4. On the other hand, 100% of isolates from non-contaminated area grew at 16 mg L-1, 87.4% at 40mg L-1 and only 19.4% of them were capable of growing at 80 mgL-1 of CuSO4. The semiquantitative assay showed that the isolated strains from the sediments of the contaminated site were resistant up to the highest concentration tested (1000 mgL-1) with the exception of AB2C strain; however, the strains isolated from non-contaminated sediments were sensitive to Cu2+ concentrations higher than 200 and 400 mgL-1, respectively. Microbial growth of AB0 strain in presence of 39mg L-1 copper showed an inhibition of 32% after 6 days of incubation as compared to the control, and copper residual concentration indicated a reduction in the supernatant of 71.2% after 6 days of incubation: pellet acid digestion proved that copper was accumulated by the cells. All these characterized actinomycete strains showed a high potential to bioremediate heavy metals. Also, it is important to notice the capacity of these strains to accumulate these toxics intracellularly.