Inherent antioxidant activity and high yield production of antioxidants in Phanerochaete chrysosporium

Phosphorus-solubilizing bacteria improve the growth of Nicotiana benthamiana on lunar regolith simulant by dissociating insoluble inorganic phosphorus

In-situ utilization of lunar soil resources will effectively improve the self-sufficiency of bioregenerative life support systems for future lunar bases. Therefore, we have explored the microbiological method to transform lunar soil into a substrate for plant cultivation. In this study, five species of phosphorus-solubilizing bacteria are used as test strains, and a 21-day bio-improving experiment with another 24-day Nicotiana benthamiana cultivation experiment are carried out on lunar regolith simulant. We have observed that the phosphorus-solublizing bacteria Bacillus mucilaginosus, Bacillus megaterium, and Pseudomonas fluorescens can tolerate the lunar regolith simulant conditions and dissociate the insoluble phosphorus from the regolith simulant. The phosphorus-solubilizing bacteria treatment improves the available phosphorus content of the regolith simulant, promoting the growth of Nicotiana benthamiana. Here we demonstrate that the phosphorus-solubilizing bacteria can effectively improve the fertility of lunar regolith simulant, making it a good cultivation substrate for higher plants. The results can lay a technical foundation for plant cultivation based on lunar regolith resources in future lunar bases.

Phenamacril and carbendazim regulate trichothecene mycotoxin synthesis by affecting ROS levels in F. asiaticum

Fusarium head blight caused by Fusarium asiaticum is an important cereal crop disease, and the trichothecene mycotoxins produced by F. asiaticum can contaminate wheat grain, which is very harmful to humans and animals. To effectively control FHB in large areas, the application of fungicides is the major strategy; however, the application of different types of fungicides has varying influences on the accumulation of trichothecene mycotoxins in F. asiaticum. In this study, phenamacril inhibited trichothecene mycotoxin accumulation in F. asiaticum; however, carbendazim (N-1H-benzimidazol-2-yl-carbamic acid, methyl ester) induced trichothecene mycotoxin accumulation. Additionally, phenamacril led to a lower level of reactive oxygen species (ROS) by inducing gene expression of the catalase and superoxide dismutase (SOD) pathways in F. asiaticum, whereas carbendazim stimulated ROS accumulation by inhibiting gene expression of the catalase and SOD pathways. Based on these results, we conclude that phenamacril and carbendazim regulate trichothecene mycotoxin synthesis by affecting ROS levels in F. asiaticum.

Effect of tebuconazole and trifloxystrobin on Ceratocystis fimbriata to control black rot of sweet potato: processes of reactive oxygen species generation and antioxidant defense responses

Black rot, caused by Ceratocystis fimbriata, is one of the most destructive disease of sweet potato worldwide, resulting in significant yield losses. However, a proper management system can increase resistance to this disease. Therefore, this study investigated the potential of using tebuconazole (TEB) and trifloxystrobin (TRI) to improve the antioxidant defense systems in sweet potato as well as the inhibitory effects on the growth of and antioxidant activity in C. fimbriata. Four days after inoculating cut surfaces of sweet potato disks with C. fimbriata, disease development was reduced by different concentrations of TEB + TRI. Infection by C. fimbriata increased the levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and electrolyte leakage (EL), and the activity of lipoxygenase (LOX) by 138, 152, 73, and 282%, respectively, in sweet potato disks, relative to control. In the sweet potato disks, C. fimbriata reduced the antioxidant enzyme activities as well as the contents of ascorbate (AsA) and reduced glutathione (GSH) by 82 and 91%, respectively, compared with control. However, TEB + TRI reduced the oxidative damage in the C. fimbriata-inoculated sweet potato disks by enhancing the antioxidant defense systems. On the other hand, applying TEB + TRI increased the levels of H₂O₂, MDA, and EL, and increased the activity of LOX in C. fimbriata, in which the contents of AsA and GSH decreased, and therefore, inhibited the growth of C. fimbriata. These results suggest that TEB + TRI can significantly control black rot disease in sweet potato by inhibiting the growth of C. fimbriata.

Rhizobium leguminosarum Glutathione Peroxidase Is Essential for Oxidative Stress Resistance and Efficient Nodulation

Glutathione (GSH) plays a key role in regulating the cellular Redox Homeostasis, and appears to be essential for initiation and development of root nodules. Glutathione peroxidase (Gpx) catalyzes the reduction of H₂O₂ and organic hydroperoxides by oxidation of GSH to oxidized GSH (GSSG), which in turn is reduced by glutathione reductase (GR). However, it has not been determined whether the Rhizobium leguminosarum Gpx or GR is required during symbiotic interactions with pea. To characterize the role of glutathione-dependent enzymes in the symbiotic process, single and double mutants were made in gpxA (encoding glutathione peroxidase) and gshR (encoding glutathione reductase) genes. All the mutations did not affect the rhizobial growth, but they increased the sensitivity of R. leguminosarum strains to H₂O₂. Mutant in GpxA had no effect on intracellular GSH levels, but can increase the expression of the catalase genes. The gshR mutant can induce the formation of normal nodules, while the gpxA single and double mutants exhibited a nodulation phenotype coupled to more than 50% reduction in the nitrogen fixation capacity, these defects in nodulation were characterized by the formation of ineffective nodules. In addition, the gpxA and gshR double mutant was severely impaired in rhizosphere colonization and competition. Quantitative proteomics using the TMT labeling method was applied to study the differential expression of proteins in bacteroids isolated from pea root nodules. A total of 27 differentially expressed proteins were identified in these root bacteroids including twenty down-regulated and seven up-regulated proteins. By sorting the down-regulated proteins, eight are transporter proteins, seven are dehydrogenase, deoxygenase, oxidase, and hydrolase. Moreover, three down-regulating proteins are directly involved in nodule process.

Characteristics of oxidative stress and antioxidant defenses by a mixed culture of acidophilic bacteria in response to Co2+ exposure

During bioleaching of Cobalt from waste lithium-ion batteries, the biooxidation activity of acidophilic bacteria is inhibited by a high concentration of Co ion in the liquid phase. However, the mechanism for Co²⁺ toxicity to acidophilic bacteria has not been fully elucidated. In this study, the effects of Co²⁺ concentration on the biooxidation activity for Fe²⁺, intracellular reactive oxygen species (ROS) level and antioxidant defense systems in a mixed-culture of acidophilic bacteria (MCAB) were investigated. The results showed that the biooxidation activity of the MCAB was inhibited by Co²⁺. Furthermore, it was indicated that the intracellular ROS contents of the MCAB under conditions of 0.4 M and 0.6 M Co²⁺ were 2.60 and 3.34 times higher than that under the condition of 0 M Co²⁺. The increase in intracellular malondialdehyde content indicated that the oxidative damage was induced by Co²⁺. Moreover, the antioxidant systems in MCAB were affected by Co²⁺. It was observed that the Co²⁺ exposure increased the catalase and glutathione peroxidase activities while reducing the superoxide dismutase activity and the intracellular glutathione (GSH) content. It was found that an exogenous GSH supplementation eliminated excess intracellular ROS and improved the biooxidation activity of the MCAB.

Oxidative Stress Induced by Metal Ions in Bioleaching of LiCoO2 by an Acidophilic Microbial Consortium

An acidophilic microbial consortium (AMC) was used to investigate the fundamental mechanism behind the adverse effects of pulp density increase in the bioleaching of waste lithium ion batteries (WLIBs). Results showed that there existed the effect of metal-ion stress on the bio-oxidative activity of AMC. The Li+ and Co2+ accumulated in the leachate were the direct cause for the decrease in lithium and cobalt recovery yields under a high pulp density. In a simulated bioleaching system with 4.0% (w ⋅v-1) LiCoO2, the intracellular reactive oxygen species (ROS) content in AMC increased from 0.82 to 6.02 within 24 h, which was almost three times higher than that of the control (2.04). After the supplementation of 0.30 g⋅L-1 of exogenous glutathione (GSH), the bacterial intracellular ROS content decreased by 40% within 24 h and the activities of intracellular ROS scavenging enzymes, including glutathione peroxidase (GSH-Px) and catalase (CAT), were 1.4- and 2.0-folds higher in comparison with the control within 24 h. In the biofilms formed on pyrite in the bioleaching of WLIBs, it was found that metal-ion stress had a great influence on the 3-D structure and the amount of biomass of the biofilms. After the exogenous addition of GSH, the structure and the amount of biomass of the biofilms were restored to some extent. Eventually, through ROS regulation by the exogenous addition of GSH, very high metal recovery yields of 98.1% Li and 96.3% Co were obtained at 5.0% pulp density.

Glutathione is Involved in Detoxification of Peroxide and Root Nodule Symbiosis of Mesorhizobium huakuii

Legumes interact with symbiotic rhizobia to produce nitrogen-fixation root nodules under nitrogen-limiting conditions. The contribution of glutathione (GSH) to this symbiosis and anti-oxidative damage was investigated using the M. huakuii gshB (encoding GSH synthetase) mutant. The gshB mutant grew poorly with different monosaccharides, including glucose, sucrose, fructose, maltose, or mannitol, as sole sources of carbon. The antioxidative capacity of gshB mutant was significantly decreased by these treatments with H₂O₂ under the lower concentrations and cumene hydroperoxide (CUOOH) under the higher concentrations, indicating that GSH plays different roles in response to organic peroxide and inorganic peroxide. The gshB mutant strain displayed no difference in catalase activity, but significantly lower levels of the peroxidase activity and the glutathione reductase activity than the wild type. The same level of catalase activity could be associated with upregulation of the transcriptional activity of the catalase genes under H₂O₂-induced conditions. The nodules infected by the gshB mutant were severely impaired in abnormal nodules, and showed a nodulation phenotype coupled to a 60% reduction in the nitrogen fixation capacity. A 20-fold decrease in the expression of two nitrogenase genes, nifH and nifD, is observed in the nodules induced by gshB mutant strain. The symbiotic deficiencies were linked to bacteroid early senescence.

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.