Role of the antioxidant defense system during the production of lignocellulolytic enzymes by fungi

Fungi are used for the production of several compounds and the efficiency of biotechnological processes is directly related to the metabolic activity of these microorganisms. The reactions catalyzed by lignocellulolytic enzymes are oxidative and generate reactive oxygen species (ROS). Excess of ROS can cause serious damages to cells, including cell death. Thus, the objective of this work was to evaluate the lignocellulolytic enzymes produced by Pleurotus sajor-caju CCB020, Phanerochaete chrysosporium ATCC 28326, Trichoderma reesei RUT-C30, and Aspergillus niger IZ-9 grown in sugarcane bagasse and two yeast extract (YE) concentrations and characterize the antioxidant defense system of fungal cells by the activities of superoxide dismutase (SOD) and catalase (CAT). Pleurotus sajor-caju exhibited the highest activities of laccase and peroxidase in sugarcane bagasse with 2.6 g of YE and an increased activity of manganese peroxidase in sugarcane bagasse with 1.3 g of YE was observed. However, P. chrysosporium showed the highest activities of exoglucanase and endoglucanase in sugarcane bagasse with 1.3 g of YE. Lipid peroxidation and variations in SOD and CAT activities were observed during the production of lignocellulolytic enzymes and depending on the YE concentrations. The antioxidant defense system was induced in response to the oxidative stress caused by imbalances between the production and the detoxification of ROS

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Role of the antioxidant defense system during the production of lignocellulolytic enzymes by fungi.

Fungi are used for the production of several compounds and the efficiency of biotechnological processes is directly related to the metabolic activity of these microorganisms. The reactions catalyzed by lignocellulolytic enzymes are oxidative and generate reactive oxygen species (ROS). Excess of ROS can cause serious damages to cells, including cell death. Thus, the objective of this work was to evaluate the lignocellulolytic enzymes produced by Pleurotus sajor-caju CCB020, Phanerochaete chrysosporium ATCC 28326, Trichoderma reesei RUT-C30, and Aspergillus niger IZ-9 grown in sugarcane bagasse and two yeast extract (YE) concentrations and characterize the antioxidant defense system of fungal cells by the activities of superoxide dismutase (SOD) and catalase (CAT). Pleurotus sajor-caju exhibited the highest activities of laccase and peroxidase in sugarcane bagasse with 2.6 g of YE and an increased activity of manganese peroxidase in sugarcane bagasse with 1.3 g of YE was observed. However, P. chrysosporium showed the highest activities of exoglucanase and endoglucanase in sugarcane bagasse with 1.3 g of YE. Lipid peroxidation and variations in SOD and CAT activities were observed during the production of lignocellulolytic enzymes and depending on the YE concentrations. The antioxidant defense system was induced in response to the oxidative stress caused by imbalances between the production and the detoxification of ROS.

Abscisic acid-deficient sit tomato mutant responses to cadmium-induced stress.

There is a very effective cross-talk between signals triggered by reactive oxygen species and hormonal responses in plants, activating proteins/enzymes likely to be involved in stress tolerance. Abscisic acid (ABA) is known as a stress hormone that takes part in the integration of signals. This work aimed to characterize the biochemical response and ultrastructural changes induced by cadmium (Cd) in the Micro-Tom (MT) sitiens ABA-deficient mutant (sit) and its wild-type (MT) counterpart. MT and sit plants were grown over a 96-h period in the presence of Cd (0, 10, and 100 µM CdCl2). The overall results indicated increases in lipid peroxidation, hydrogen peroxide content and in the activities of the key antioxidant enzymes such as catalase, glutathione reductase, and ascorbate peroxidase in both genotypes. On the other hand, no alteration was observed in chlorophyll content, while the activity of another antioxidant enzyme, superoxide dismutase, remained constant or even decreased in the presence of Cd. Roots and shoots of the sit mutant and MT were analyzed by light and transmission electron microscopy in order to characterize the structural changes caused by the exposure to this metal. Cd caused a decrease in intercellular spaces in shoots and a decrease in cell size in roots of both genotypes. In leaves, Cd affected organelle shape and internal organization of the thylakoid membranes, whereas noticeable increase in the number of mitochondria and vacuoles in MT and sit roots were observed. These results add new information that should help unravel the relative importance of ABA in regulating the cell responses to stressful conditions induced by Cd apart from providing the first characterization of this mutant to oxidative stress.

Evaluation of sugar-cane vinasse treated with Pleurotus sajor-caju utilizing aquatic organisms as toxicological indicators.

Toxicity tests with aquatic organisms constitute an effective tool in the evaluation, prediction and detection of the potential effect of pollutants from environmental samples in living organisms. Vinasse, a highly colored effluent, is a sub-product rich in nutrients, mainly organic matter, with high pollutant potential when disposed in the environment. Assays for vinasse decolorization were performed using the fungus Pleurotus sajor-caju CCB020 in vinasse biodegradation study, were occurred reductions of 82.8% in COD, 75.3% in BOD, 99.2% in the coloration and 99.7% in turbidity. The vinasse toxicity reduction was determined by the exposition to the following organisms: Pseudokirchneriella subcapitata, Daphnia magna, Daphnia similis and Hydra attenuata. This work concluded that the systematic combination of P. sajor-caju and vinasse can be applied in the bioprocess of color reduction and degradation of complex vinasse compounds, with reduction in the toxicity and improving its physical-chemical properties.

Antioxidant metabolism of coffee cell suspension cultures in response to cadmium.

The antioxidant responses of coffee (Coffea arabica L.) cell suspension cultures to cadmium (Cd) were investigated. Cd accumulated very rapidly in the cells and this accumulation was directly correlated with an increase in applied CdCl(2) concentration in the external medium. At 0.05mM CdCl(2), growth was stimulated, but at 0.5mM CdCl(2), the growth rate was reduced. An alteration in activated oxygen metabolism was detected by visual analysis as well as by an increase in lipid peroxidation at the higher CdCl(2) concentration. Catalase (CAT; EC 1.11.1.6), glutathione reductase (GR; EC 1.6.4.2) and superoxide dismutase (SOD; EC 1.15.1.1) activity increased, particularly at the higher concentration of CdCl(2). Ascorbate peroxidase (APX; EC 1.11.1.11) activity was increased at the lower CdCl(2) concentration used, but could not be detected in cells growing in the higher CdCl(2) concentration after 24h of growth, whilst guaiacol peroxidase (GOPX; EC 1.11.1.7) did not show a clear response to Cd treatment. An analysis by non-denaturing PAGE followed by staining for enzyme activity, revealed one CAT isoenzyme, nine SOD isoenzymes and four GR isoenzymes. The SOD isoenzymes were differently affected by CdCl(2) treatment and one GR isoenzyme was shown to specifically respond to CdCl(2). The results suggest that the higher concentrations of CdCl(2) may lead to oxidative stress. The main response appears to be via the induction of SOD and CAT activities for the removal of reactive oxygen species (ROS), and by the induction of GR to ensure the availability of reduced glutathione for the synthesis of Cd-binding peptides, which may also be related to the inhibition of APX activity probably due to glutathione and ascorbate depletion.