Characterization And Mechanism Of Cr(?) Removal By Penicillium Oxalicum SL2

Cr?VI?pollution is a global environmental concern as it threatens the environment and human health.Bioremediation of Cr???pollution using microbes is a hotspot as it has a lot of advantages compared to conventional physicochemical techniques,including completely remediation,low cost and environmental friendly.Given that there is still lacking strong functional strain and knowledge on the mechanisms of bioremediation process,we isolated a fungal strain from indoor air in the present study.By using Gompertz model and response surface model to analyze the salt-Cr???tolerance and optimizing the conditions of removing chroumium,respectively.Moreover,ion chromatography,Fourier transform infrared spectroscopy,synchrotron radiation X-ray fluorescence spectroscopy and soft X-ray microbeam lines were employed to illustrate the mechanisms of Cr???removal.The existence of reductase gene was proven by using high throughput transcriptome sequencing to study the strain's responses to Cr???.All these explorations provide scienctific and technological support for microbial remediation of Cr???.The main findings are as follows:?1?A Cr???tolerant and reductive filamentous fungus strain was isolated from indoor air and proved to be a new candidate for application in Cr???bioremediation.According to the morphological,physiological and biochemical characteristics and ribosomal gene sequence?18S rDNA,26S rDNA and ITS?analysis,the isolated fungi SL2 belongs to Penicillium oxalicum.P.oxalicum SL2 is a salt and Cr?VI?-resistance microorganism,whose growth pattern can be well simulated by Gompertz model.In electroplating wastewater with initial Cr???concentration of 102.2mg/L,P.oxalicum SL2 can completely remove Cr???within 6 days by uptake and reduction,showing good potential for application.?2?Conditions for Cr???removal by P.oxalicum SL2 were optimized.Cr???removal by P.oxalicum SL2 is affected by culture methods and environmental factors.The effects of initial pH,Cr???concentration and salinity on Cr???removal rate by P.oxalicum SL2 can be described by a regression equation.When pH,Cr???concentration and added NaCl are 8.11,376.21 mg/L and 25.00 g/L,respectively,the Cr???removal rate reaches the peak of 2.28 mgL-1h-1.?3?Mechanisms of Cr???removal by P.oxalicum SL2 were studied.SL2 can remove Cr???by reduction using oxalic acid as an agent,whose secretion is promoted in the presence of Cr???.In addition,SL2 can remove Cr???by uptake using hydroxyl,amine,carboxyl,and phosphate groups as interaction sites between the biomass and Cr???.Chromium uptake by the biomass is distributed both inside and on surface of the mycelia.The speciation of chromium in the mycelia is found as Cr-Cys and CrPO4 at the early stage,which transform to[Cr?C2O4?3]3-ion later.?4?Transcriptional-level responses of P.oxalicum SL2 to Cr???stress were investigated.The genes related to cell wall compositions and phosphate ion transport are significantly different expressed between P.oxalicum SL2 which can tolerate Cr???and P.oxalicum CFCC which canot tolerate Cr???,suggesting they are relevant to Cr???tolerance of strains of P.oxalicum.In addition,the genes related to organic acid metabolism,energy metabolism,stress response and DNA repair are significantly different expressed when P.oxalicum SL2 grows in Cr???and non-Cr???condictions,which represent the response of P.oxalicum SL2 to Cr???stress.Moreover,the enrichment pathways of different gene expressions in P.oxalicum SL2 are influenced by time,concentration.?5?The existence and expression of Cr???reductase genes in fungi were confirmed.The Cr???reductase genes are found in strains of?P.oxalicum.PDE₀5019,PDE₀7956 and PDE₀1864 are expressed in both P.oxalicum SL2 and P.oxalicum CFCC,while PDE₀3621 only expressed in P.oxalicum SL2.The expressions of these Cr???reductase genes in P.oxalicum SL2 is affected by growth period and Cr???stress.