Improving the thermostability of Trichoderma reesei xylanase 2 by introducing disulfide bonds

Background: Xylanases are considered one of the most important enzymes in many industries. However, their low thermostability hampers their applications in feed pelleting, pulp bleaching, and so on. The main aim of this work was to improve the thermostability of Trichoderma ressei xylanase 2 (Xyn2) by introducing disulfide bonds between the N-terminal and α-helix and the ß-sheet core. Results: In this work, two disulfide bonds were separately introduced in the Xyn2 to connect the N-terminal and α-helix to the ß-sheet core of Xyn2. The two disulfide bonds were introduced by site-directed mutagenesis of the corresponding residues. The half-life of the mutants Xyn2C14­52 (disulfide bond between ß-sheets B2 and B3) and Xyn2C59­149 (disulfide bond between ß-sheets A5 and A6) at 60°C was improved by approximately 2.5- and 1.8-fold compared to that of the wild type Xyn2. In addition, the enzyme's resistance to alkali and acid was enhanced. Conclusion: Our results indicated that the connection of the N-terminal and α-helix to the ß-sheet core is due to the stable structure of the entire protein.

Avaliação da toxicidade de efluentes de branqueamento de pasta celulósica pré e pós-degradação biológica / Evaluation of the toxicity of effluents from pulp bleaching before and after biological degradation

A fábrica de papel e celulose gera vazões elevadas de efluente, sendo este de difícil tratamento por possuir alta carga de matéria orgânica, organoclorados, lignina e carboidratos. O tratamento biológico é o mais utilizado atualmente. Este trabalho avaliou a eficiência de remoção de toxicidade desse efluente após degradação biológica, através de ensaios ecotoxicológicos. Foram realizados ensaios de toxicidade crônica e aguda, conforme normas da Associação Brasileira de Normas Técnicas (ABNT). Foram feitos dois reatores de degradação aeróbica, sendo um mesofílico (30°C) e outro termofílico (55°C), avaliando também qual o melhor sistema. Os resultados demonstraram que a degradação biológica é capaz até de anular a toxicidade aguda, porém a toxicidade crônica permanece presente. O sistema de degradação mesofílico foi o mais eficiente; e o efluente alcalino foi o de maior toxicidade antes do tratamento.

The pulp and paper mill generates high flow rates of wastewater, which is difficult to treat because of its high load of organic matter, organochlorines, lignin and cellulose. Nowadays, the biological treatment is the most widely used by industries. This study aims to evaluate the toxicity removal efficiency of the effluent after biological degradation through ecotoxicological tests. Trials of acute and chronic toxicity studies were performed as the Brazilian Technical Standards Association (ABNT). Two reactors were made of aerobic degradation, one mesophilic (30°C) and other thermophilic (55 °C), also evaluating which is the best system. The results demonstrated that the biological degradation can even eliminate acute toxicity, however, chronic toxicity remains present. The system of mesophilic degradation was more efficient and the alkaline effluent showed greater toxicity before treatment.