title: Cadmium removal by Euglena gracilis is enhanced under anaerobic growth conditions.
abstract: The facultative protist Euglena gracilis, a heavy metal hyper-accumulator, was grown under photo-heterotrophic and extreme conditions (acidic pH, anaerobiosis and with Cd(2+)) and biochemically characterized. High biomass (8.5×10(6)cellsmL(-1)) was reached after 10 days of culture. Under anaerobiosis, photosynthetic activity built up a microaerophilic environment of 0.7% O₂, which was sufficient to allow mitochondrial respiratory activity: glutamate and malate were fully consumed, whereas 25-33% of the added glucose was consumed. In anaerobic cells, photosynthesis but not respiration was activated by Cd(2+) which induced higher oxidative stress. Malondialdehyde (MDA) levels were 20 times lower in control cells under anaerobiosis than in aerobiosis, although Cd(2+) induced a higher MDA production. Cd(2+) stress induced increased contents of chelating thiols (cysteine, glutathione and phytochelatins) and polyphosphate. Biosorption (90%) and intracellular accumulation (30%) were the mechanisms by which anaerobic cells removed Cd(2+) from medium, which was 36% higher versus aerobic cells. The present study indicated that E. gracilis has the ability to remove Cd(2+) under anaerobic conditions, which might be advantageous for metal removal in sediments from polluted water bodies or bioreactors, where the O₂ concentration is particularly low.
authors.affiliation: Departamento de Bioquímica, Instituto Nacional de Cardiología, Mexico.
authors.forename: M Geovanni
authors.initials: MG
authors.lastname: Santiago-Martínez
authors.affiliation: Departamento de Bioquímica, Instituto Nacional de Cardiología, Mexico.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Lira-Silva
authors.affiliation: Departamento de Bioquímica, Instituto Nacional de Cardiología, Mexico.
authors.forename: Rusely
authors.initials: R
authors.lastname: Encalada
authors.affiliation: Departamento de Bioquímica, Instituto Nacional de Cardiología, Mexico.
authors.forename: Erika
authors.initials: E
authors.lastname: Pineda
authors.affiliation: Departamento de Bioquímica, Instituto Nacional de Cardiología, Mexico.
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Gallardo-Pérez
authors.affiliation: Facultad de Medicina, UNAM, Mexico City, Mexico.
authors.forename: Armando
authors.initials: A
authors.lastname: Zepeda-Rodriguez
authors.affiliation: Departamento de Bioquímica, Instituto Nacional de Cardiología, Mexico.
authors.forename: Rafael
authors.initials: R
authors.lastname: Moreno-Sánchez
authors.affiliation: Departamento de Bioquímica, Instituto Nacional de Cardiología, Mexico.
authors.forename: Emma
authors.initials: E
authors.lastname: Saavedra
authors.affiliation: Departamento de Bioquímica, Instituto Nacional de Cardiología, Mexico. Electronic address: rjass_cardiol@yahoo.com.mx.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Jasso-Chávez
mesh_terms: D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D018533:Biomass; D019149:Bioreactors; D002104:Cadmium / Q000378:metabolism* / Q000494:pharmacology; D002244:Carbon / Q000378:metabolism; D003470:Culture Media; D005056:Euglena gracilis / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D006019:Glycolysis; D007700:Kinetics; D010788:Photosynthesis
chemical_list: D003470:Culture Media; D002104:Cadmium; D002244:Carbon
keywords: Anaerobic metabolism; Biomass production; Biosorption; Cadmium pollution; Heavy metal toxicity