Atividade específica do extrato bruto e estabilidade a diferentes temperaturas e valores de pH de xilanases extracelulares bacterianas

• Ano de defesa: 2014
• Autor(a) principal: Sampaio, Carlos Rodolfo
• Orientador(a): Fernandes, Marcelo Ferreira
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Sergipe
• Programa de Pós-Graduação: Pós-Graduação em Biotecnologia de Recursos Naturais
• País: BR
• Palavras-chave em Português: Biotecnologia; Enzimas; Aplicações industriais; Bactérias; Polpa de madeira; Branqueamento; Xilanases; Clareamento de polpa Kraft; Diversidade microbiana; Sacarificação; Enzimas termoestáveis
• Palavras-chave em Inglês: Kraft pulp bleaching; Microbial diversity; Saccharification; Non-culturable viable; Thermostable enzymes
• Área do conhecimento CNPq: CNPQ::CIENCIAS BIOLOGICAS::MICROBIOLOGIA
• Link de acesso: https://ri.ufs.br/handle/riufs/3302

Xylanases have an important role as biocatalysts in different agroindustrial processes, such as saccharification of plant residues for the production of ethanol and bleaching of wood pulp for the production of pulp. On an industrial scale, these processes may require extreme pH or temperature, which require enzymes compatible with these conditions. Most enzymes available or showing commercial potential is synthesized by fungi or bacteria belonging to a few genera. Evaluation of rare isolation bacteria is an important strategy to expand the diversity of xylanases and their potential in terms of activity, stability and technological application. The aim of this study was to evaluate a collection of common and rare isolation soil bacteria regarding to xylanase activity and characterize the stability conditions of temperature and pH. The analyzed collection consists of 120 isolates with representatives from six phyla that were subjected to screening for xylanase activity in pure cultures and in the extracellular proteic extract (EPE). The ratio between the halos diameters of xylan hydrolysis and in the colonies on solid medium (ratio H:C), incubated at 30 ° C for up to 14 days, was used for the evaluation of cultures as a selection criteria. The effects of different sources of variation in the bacteria isolation stage (original soil, culture medium, solidifying agent, inoculum dilution and plating method and incubation time to colony appearance) and the group of bacterial isolation (rare or common) on the frequency of isolates with high xylanase activity were evaluated based on the ratio H:C. EPEs were obtained in liquid media containing xylan inoculated with the eleven isolates with highest ratios H:C. The extracts were evaluated for the specific xylanase activity at 50 °C for 1 h. Extracts of the three isolates with the highest potential for activity under this condition were evaluated for optimum activity, stability, activity at 60 oC and at pH 4.0, 5.5 and 8.0. Twenty-two isolates (25%), including eight from rare isolation, showed xylanase activity under the conditions evaluated, and found a high variability (> 230%) between these isolates. No isolation factor or rare or common isolation condition were associated with efficiency of xylanase activity in solid medium. High variability in specific xylanase activity in EPEs was also found among isolates (1500%), highlighting two rare isolates (TC119 and TC21), from Alfaproteobacteria class, and one common isolate (TC99), from Ralstoniaceae family. Extracellular xylanases from TC21 and TC119 showed high relative activity at temperatures up to 70 oC and were insensitive to pH in the range 4.0 to 8.0; however, TC99 isolate showed optimum temperature at 40 °C and low stability to temperature and pH. Extracellular xylanases from TC119 showed no cellulolytic activity. Rare isolation soil bacteria show high potential as a source of extracellular xylanases adapted to extreme pH and temperature conditions, which are required in agroindustrial processes.