Adaptability And Resistance Of Phanerochaete Chrysosporium With Cd (Ⅱ) In Wastewater Treatment

An increasing amount of toxic heavy metals wastes, such as cadmium, mercury, vanadium, are being discharged into the environment, which caused serious water, air, and soil pollution. The heavy metals was seriously harmful to human beings because they are difficult to remove and easy to enrich in organisms and human baby. Cadmium, as one of the toxic heavy metals, can cause the damage of kidney, liver and bone system. Since the appearance of the cadmium induced "itai-itai disease" in Japan in1950s, cadmium and other heavy metals have received much attention from environmentalists and scientists.Cadmium removal from wastewater has traditionally been accomplished using chemical precipitation, ion exchange, membrane separation and activated carbon adsorption and et al. However, some drawbacks, such as high cost, low efficiency, labor intensiveness and the resulting secondary pollution, hinder the improvement of these techniques. Bioremediation, in which microorganisms are used to remove pollutants, was widely accepted and applied in the field of heavy metal pollution owing to the cost effectiveness, environmental compatibility, and high efficiency of the technology. White-rot fungi, especially the model strain Phanerochaete chrysosporium, was been proved to be a kind of organism for adsorping heavy metals efficiently. At present, the research of white rot fungi and heavy metals mostly focused on the optimization of adsorption conditions, mainly including pretreatment methods and liquid pH, temperature, initial concentration of heavy metal ions and mutual influence of coexisting ions, etc., the research of the interaction between fungi and heavy metal ions and the adsorption mechanism are still rare.On the basis of previous studies, the adaptability and resistance of Phanerochaete chrysosporium with Cd (Ⅱ) in wastewater treatment were studied. The production of glutathione and oxalate in Phanerochaete chrysosporium was investigated and the oxidative stress induced responses was determined, including morphological changes, pH changes of the medium, lipid peroxidation, and analyse their connection with GSH and oxalate secretion.The changes of morphology and physiology under Cd(Ⅱ) stress was investigated, and at the same time the influence on cadmium adsorption by Phanerochaete chrysosporium was studied. Based on our study, we found that the color of the fungi was turned pale yellow from ivory white and the diameter of mycelium pellets was decreased to2～3mm from4～6mm when the Cd(Ⅱ) content increased from0mg/L to25mg/L. It was clear from the SEM micrographs that some cadmium crystals were adsorbed on the mycelia, and some mycelia had shrunk under Cd(Ⅱ) stress.The research of the glutathione and oxalate responses was shown that:the level of glutathione (including reduced and oxidation type) and oxalate were closely related to Cd(II) content with time. The glutathione (including reduced and oxidation type) content increased from6.492nmol/g to7.02nmol/g, and the oxalate concentration increased from86.2664μmol/g to145.90μmol/g when the cadmium content increased from0mg/L to25mg/L, and the exposure time entended from0h to24h. The maximum production determined was7.02nmol/g for glutathione and145.90μmol/g for oxalate when the Cd(II) content was25mg/L. The above results might show that appropriate addition of cadmium could promote the production of glutathione and oxalate. The value of GSH/GSSG in our experiments was decreased from3.785to2.316, indicating that the oxidized glutathione increased faster than reduced glutathione. Interestingly, malondialdehyde concentration, as a reliable indicator of the cadmium biotoxicity, decreased with the increase of glutathione and oxalate, indicating that accumulation of glutathione and oxalate played an important role in alleviation of cadmium toxicity.In addition, we could found that the process of Cd(II) adsorption by Phanerochaete chrysosporium could be divided into three stages:the first stage is the first4h, which the adsorption quantity increased as a logarithmic growth trend; the second stage is the following4-12h, which the adsorption quantity increased slower than the previous stage, and increased as a linear growth trend; The third stage is the time after12h under cadmium stress, which the Cd(II) adsorption quantity of Phanerochaete chrysosporium reached to the balance at this stage. In this experiment, we also found the highest adsorption efficiency of Cd(II) by Phanerochaete chrysosporium was56.5%.