High osmotic stress improves electro-transformation efficiency of fission yeast

The efficient treatment of mature landfill leachate using tower bipolar electrode flocculation-oxidation combined with electrochemical biofilm reactors

Mature landfill leachate contains high concentrations of organic and inorganic compounds that inhibit the performance of conventional biological treatment. Nowadays, few single treatment techniques could fulfill the requirements of cleaning mature landfill leachate. In this study, a tower bipolar electrode flocculation-oxidation (BEF-O) reactor and an electrochemical biofilm reactor (EBR) combine device was constructed to effectively treat mature landfill leachate. And the removal efficiency and mechanism of various pollutants using the BEF-O reactor were investigated. The BEF-O system with the current density of 100 mA/cm² shows excellent treatment efficiency, which can roundly remove most pollutants (NH₄⁺-N, COD and heavy metals, etc.), and increase the bioavailability of the effluent to facilitate subsequent EBR treatment. Benefiting from the metabolic stimulation and population selection effect of electric current on microorganisms, EBR has a denser biofilm, stronger anti-pollution load capacity, superior, and stable pollution treatment efficiency. More importantly, the combined device can reduce the concentrations of COD and NH₄⁺-N from 6410 to 338 mg/L and 4065 to 4 mg/L, respectively, and has an economical energy consumption of 32.02 kWh/(kg COD) and 54.04 kWh/ (kg NH₄⁺-N). To summarize, this research could provide an innovative and industrial application prospect technology for the mature landfill leachate treatment.

Proximity-dependent biotin labelling in yeast using the engineered ascorbate peroxidase APEX2

The engineered ascorbate peroxidase (APEX2) has been effectively employed in mammalian cells to identify protein-protein interactions. APEX2 fused to a protein of interest covalently tags nearby proteins with biotin-phenol (BP) when H2O2 is added to the cell culture medium. Subsequent affinity purification of biotinylated proteins allows for identification by MS. BP labelling occurs in 1 min, providing temporal control of labelling. The APEX2 tool enables proteomic mapping of subcellular compartments as well as identification of dynamic protein complexes, and has emerged as a new methodology for proteomic analysis. Despite these advantages, a related APEX2 approach has not been developed for yeast. Here we report methods to enable APEX2-mediated biotin labelling in yeast. Our work demonstrated that high osmolarity and disruption of cell wall integrity permits live-cell biotin labelling in Schizosaccharomyces pombe and Saccharomyces cerevisiae respectively. Under these conditions, APEX2 permitted targeted and proximity-dependent labelling of proteins. The methods described herein set the stage for large-scale proteomic studies in yeast. With modifications, the method is also expected to be effective in other organisms with cell walls, such as bacteria and plants.

Different effects of sodium chloride preincubation on cadmium tolerance of Pichia kudriavzevii and Saccharomyces cerevisiae

Application of growing microorganisms for cadmium removal is restricted by high cadmium toxicity. The effects of sodium chloride (NaCl) preincubation on the cadmium tolerance and removal ability of Pichia kudriavzevii and Saccharomyces cerevisiae were investigated in this study. NaCl preincubation improved the biomass of P. kudriavzevii under cadmium stress, while no obvious effect was observed in S. cerevisiae. The improved activities of peroxidase (POD) and catalase (CAT) after NaCl preincubation might be an important reason for the decrease of the reactive oxygen species (ROS) accumulation, cell death, and oxidative damage of proteins and lipids induced by cadmium, contributing to the improvement of the yeast growth. The cadmium bioaccumulation capacity of P. kudriavzevii decreased significantly after NaCl preincubation, which played an important role in mitigating the cadmium toxicity to the yeast. The cadmium removal rate of P. kudriavzevii was obviously higher than S. cerevisiae and was significantly enhanced after NaCl preincubation. The results suggested that NaCl preincubation improved the cadmium tolerance and removal ability of P. kudriavzevii.

Electrically induced protein release from Schizosaccharomyces pombe cells in a hyperosmotic condition during and following a high electropulsation

A high-electric-field application of fission yeast cells under hyperosmotic conditions improved the electro-induced release of protein and cytoplasmic enzymes. A cell suspension was pulsed at 12.5 kV/cm for 10 ms in a batch system and immediately postincubated at 30 degrees C. The total protein release rate from cells increased in the hypertonic solutions of 1.5-2.5 M sorbitol to approximately threefold higher than those in the hypotonic and isotonic solutions of 0-0.5 M sorbitol. The protein release rate in 2.0 M sorbitol greatly increased up to 4.5 h and then gradually increased after 7.5 h. The maximum activities of cytoplasmic enzymes, such as alcohol dehydrogenase and 3-phosphoglycerate kinase, were obtained at 7.5 h after electropulsation in 2.0 M sorbitol, yielding approximately 90% of the enzyme activity levels found in spheroplast lysate. On the other hand, the release rates of protease in vacuoles and invertase in periplasmic space did not depend on osmotic solutions during electric pulse application.

A rapid and simple procedure for high-efficiency lithium acetate transformation of cryopreservedSchizosaccharomyces pombe cells

A rapid, simple, convenient, and highly efficient transformation of the fission yeast Schizosaccharomyces pombe has been developed. Freezing fission yeast cells in glycerol, a permeating cryoprotectant, with lithium acetate improved remarkably the transformation efficiency by one to two orders of magnitude. The optimum concentration of glycerol was found to be 30%, which is higher than that (10-15%) in the conventional cryopreservation of yeast cells. Glycerol not only played a role in cryopreserving the competent cells but also improved the transformation efficiency of the process. The thawed cell suspension with glycerol and lithium acetate was immediately mixed with carrier DNA, plasmid DNA and polyethylene glycol. Next, the mixture was heat shocked and directly spread on a selection plate. This simple procedure yielded more than 10(6) transformants/microg plasmid DNA, reducing the time required to only 20 min in total, including the thawing time. Furthermore, the frozen competent cells were stored long-term for more than 3 months without any significant loss of efficiency.