Biological degradation of cyanide using native bacteria isolated from a cassava-processing effluent.

• Autor(a) principal: Vallenas Arévalo, Amzy Tania
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: http://www.teses.usp.br/teses/disponiveis/3/3137/tde-07012020-161413/
• topic: Bacteria; Bactérias; Biodegradação; Biodegradation; Cianeto; Cyanide; Klebsiella oxytoca; Serratia marcescens

Cyanide (CN) can be present in the environment due to human activities including gold mining, electroplating, and nylon production. During the industrial processing of cassava, cyanide is liberated in effluents due to the presence of cyanogenic glycosides in the pulp. Cyanide is toxic for most living organisms since it inhibits the action of the cytochrome c oxidase and stops the electron transport chain during cellular respiration. Because of this, cyanide-containing effluents need to be treated prior to discharge to the environment, which can be achieved by chemical, physical or biological methods. In this context, this work evaluates the cyanide-degradation capacity of native bacteria isolated from a cassava processing effluent and the best conditions for the biological removal of cyanide. In total, sixteen cyanide-resistant bacteria were isolated, identified by mass spectrometry technique MALDI-TOF, and tested individually for their ability to degrade cyanide. Eight different species were identified among the isolated strains. Four of them, belonging to the Klebsiella oxytoca, Bacillus pumilus, Corynebacterium glutamicum, and Serratia marcescens species, were selected for further assays to assess their susceptibility to pH and cyanide initial concentration. Results showed that cyanide degradation was inhibited when pH was above 9 and that higher initial cyanide concentrations resulted in lower cyanide degradation percentage. However, strains could still keep their degradation capacity even in high initial cyanide concentrations of 1000mg.L-1 . Isolated Klebsiella oxytoca and Serratia marcescens were thus selected for optimization of the degradation process by analyzing the influence of carbon source, temperature and rotation speed. Both strains showed greater degradation rates when using sodium acetate as a carbon source and incubated at 30°C. Agitation speed did not show an effect on cyanide degradation by Klebsiella oxytoca, but enhanced degradation by Serratia marcescens strain. Under optimal incubation conditions, isolated Klebsiella oxytoca and Serratia marcescens strains could degrade cyanide from a synthetic 150mg.L-1 freecyanide solution, pH 8, using sodium acetate as a carbon source by 43 and 41% after 24hour of incubation, respectively, showing their potential to be used in the biodegradation of cyanide-containing effluents.