A Potentially Practicable Halotolerant Yeast Meyerozyma guilliermondii A4 for Decolorizing and Detoxifying Azo Dyes and Its Possible Halotolerance Mechanisms.

In this study, a halotolerant yeast that is capable of efficiently decolorizing and detoxifying azo dyes was isolated, identified and characterized for coping with the treatment of azo-dye-containing wastewaters. A characterization of the yeast, including the optimization of its metabolism and growth conditions, its detoxification effectiveness and the degradation pathway of the target azo dye, as well as a determination of the key activities of the enzyme, was performed. Finally, the possible halotolerance mechanisms of the yeast were proposed through a comparative transcriptome analysis. The results show that a halotolerant yeast, A4, which could decolorize various azo dyes, was isolated from a marine environment and was identified as Meyerozyma guilliermondii. Its optimal conditions for dye decolorization were ≥1.0 g/L of sucrose, ≥0.2 g/L of (NH4)2SO4, 0.06 g/L of yeast extract, pH 6.0, a temperature of 35 °C and a rotation speed of ≥160 rpm. The yeast, A4, degraded and detoxified ARB through a series of steps, relying on the key enzymes that might be involved in the degradation of azo dye and aromatic compounds. The halotolerance of the yeast, A4, was mainly related to the regulation of the cell wall components and the excessive uptake of Na+/K+ and/or compatible organic solutes into the cells under different salinity conditions. The up-regulation of genes encoding Ca2+-ATPase and casein kinase II as well as the enrichment of KEGG pathways associated with proteasome and ribosome might also be responsible for its halotolerance.

Effects of chronic prometryn exposure on antioxidative status, intestinal morphology, and microbiota in sea cucumber (Apostichopus japonicus).

Prometryn is an occasional triazine herbicide used in aquaculture to kill algae. However, deposition of prometryn at the bottom of the pond poses a potential threat to aquatic animals, especially benthos, such as the sea cucumber. This study investigated the toxic effects of prometryn oral exposure on antioxidants, and the intestinal histomorphology and microbiome of sea cucumbers. Results showed that the accumulation of prometryn in the intestine, respiratory tree, and body wall decreased sequentially under the same level. Severe pathological damages were observed in the intestines of sea cucumbers fed with 0.080 and 1.595 g/kg prometryn (measured concentration). Moreover, hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations were significantly increased in prometryn treatment groups compared to the control group (P < 0.05), while the catalase (CAT) activity was significantly decreased (P < 0.05) in the coelomic fluid of treatment groups. At the phylum level, the abundance of Proteobacteria was significantly higher in the 0.080 g/kg treatment group than in the control group. In addition, prometryn exposure reduced the diversity of intestinal microflora in sea cucumbers. In conclusion, these results suggest that prometryn has potential toxicity to sea cucumber. Therefore, the harm of prometryn deposited in the sediment to aquatic animals must be a concern in aquaculture.

Magnetically stimulated azo dye biodegradation by a newly isolated osmo-tolerant Candida tropicalis A1 and transcriptomic responses.

A recently isolated osmo-tolerant yeast Candida tropicalis A1, which could decolorize various azo dyes under high-salinity conditions, was systematically characterized in the present study. Stimulating dye-decolorization effectiveness and osmo-tolerance of the yeast by static magnetic field (SMF) was investigated and transcriptomic responses of the yeast to SMF was analyzed to propose possible mechanisms. The results demonstrated that the yeast A1 effectively decolorized (≥ 97.50% within 12 h) and detoxified (from high toxicity to low toxicity within 24 h) 70 mg/L Acid Red B (ARB) under the optimized conditions through a series of steps including naphthalene-amidine bond cleavage, reductive or oxidative deamination/desulfurization, open-loop of hydroxy-substituted naphthalene or benzene and TCA cycle. Moreover, dye decolorization performance and osmo-tolerance of the yeast A1 were further improved by 24.6 mT SMF. Genes encoding high-affinity hexose/glucose transporter proteins and NADH-ubiquinone oxidoreductase were up-regulated by 24.6 mT SMF, which might be responsible for the increase of dye decolorization. Significant up-regulation of glycerol-3-phosphate dehydrogenase and cell wall protein RHD3 suggested that osmo-tolerance was enhanced by 24.6 mT SMF through promoting production and intracellular accumulation of glycerol as compatible solute, as well as regulation of cell wall component. In conclusion, 24.6 mT SMF led to the up-regulation of related genes resulting in enhanced dye biodegradation efficiency and osmo-tolerance of the yeast A1.

Aerobic decolorization and degradation of azo dyes by suspended growing cells and immobilized cells of a newly isolated yeast Magnusiomyces ingens LH-F1.

Aerobic decolorization and degradation of azo dyes by both of suspended growing cells and immobilized cells of a newly isolated yeast strain LH-F1 were investigated in this study. A yeast strain LH-F1 capable of aerobically decolorizing various azo dyes (20mg/L) was identified as Magnusiomyces ingens basing on 26S rDNA analysis. Meanwhile, effects of different parameters on decolorization of Acid Red B by both of suspended growing cells and immobilized cells of strain LH-F1 were investigated. Furthermore, possible degradation pathway of the dye was proposed through analyzing metabolic intermediates using UV-Vis and HPLC-MS methods. As far as it is known, it is the first systematic research on a M. ingens strain which is capable of efficiently decolorizing azo dyes under aerobic condition. Additionally, this work would also provide a potentially useful microbial strain LH-F1 for treatment of industrial wastewaters containing azo dyes.

Isolation, characterization and docking studies of 2,3-dihydroxybiphenyl 1,2-dioxygenase from an activated sludge metagenome.

A 2,3-dihydroxybiphenyl-1,2-dioxygenase gene (designated as bphC_meta) was identified in activated sludge metagenome by PCR. This gene shared 99% sequence identity with BphC from Burkholderia xenovorans LB400. The enzyme was purified from recombinant Escherichia coli with a subunit molecular mass of 32 ± 1 kDa. It was optimally active at pH 9.0 and 40°C, using 2,3-dihydroxybiphenyl as a substrate. Activity toward substituted catechols was: 2,3-dihydroxybiphenyl > 3-methylcatechol > catechol > 4-chlorocatechol (4-methylcatechol). The prediction made by molecular docking was consistent with the kinetic experimental data, and further explained the substrate preference of BphC_meta. The present study could pave the way for the improved understanding and application of BphCs derived from metagenomes.