| Perfluorooctanoic acid(PFOA)is one typical representative of perfluorinated organic compounds(PFCs),which are used widely in textile,chemical,mechanical,pharmaceutical,electronics and aerospace industries.Due to its persistence,bioaccumulation and biotoxicity,PFOA has been detected in various environmental media in recent years,posing a serious threat to ecological safety and human health.As a kind of novel persistent organic pollutants,remediation of PFOA pollutant has become one of the research hotspots in the field of environmental sciences.Microbial transformation is an attractive remediation technique to prevent and clean up PFOA contamination.In this work,two strains of fungi(named as AF1 and AF2)were isolated from soil around a fluoride plant by enrichment culture and gradient acclimation,using PFOA as the sole carbon source.Based on morphological characteristics and phylogenetic analysis of ITS sequences,two fungi were identified as Trichoderma asperellum and Mucor circinelloides.The study on the growth features of PFOA-degrading fungus AF1 and AF2 indicated that strain AF2 has a growth advantage,and the maximum biomass is higher than that of AF1.The degradation ability of PFOA was analyzed by LC-MS detection,the results showed that the maximum degradation rate of fungus AF1 and AF2 was 23.24±1.26% and 28.12±1.45% respectively when cultured for 96 h in inorganic salt ion medium using PFOA as the sole carbon source.Secondly,the physiological response of fungus AF2 to PFOA stress was studied.The growth curve of strain AF2 in PDB medium with PFOA concentration of 0,1000,1500,2000 mg/L has been determined,and the highest concentration of AF2 tolerance to PFOA is 1500 mg/L.The SOD,GSH activity and MDA content of strain AF2 increased significantly with the increase of PFOA stress concentration(0,300,600 mg/L),and high concentration of PFOA(900 mg/L)reduced MDA content,SOD a nd GSH activity.The results showed that strain AF2 had high PFOA tolerance,but excessive PFOA concentration could produce oxidative stress and membrane damage to PFOA-degrading fungus AF2.The fungus AF2 was fermented with a modified inorganic salt medium containing or without 500 mg/l PFOA,and the cells after culturing for 96 h and 120 h(P96,C96,P120,and C120)were collected for transcriptome sequencing and comparative transcriptome analysis.Through data filtering and splicing assembly,a total of 5,8181 unigenes were obtained with a total length of 3854,1574 bp,and 4,8731 unigenes can be annotated into individual databases by way of the transcript function annotation.The different expression gene analysis of the treatment group and the control group showed that there were 2000 different expression genes bettween group P96 and group C96,of which 694 genes were up-regulated and 1306 genes down-regulated,and there were 1244 different expression genes bettween group P120 and group C120,of which 591 genes were up-regulated and 693 genes down-regulated.Through the differential gene annotation of two comparison groups,it was found that 16 common differentially expressed genes were annotated into the xenobiotics degradation and metabolic pathways,and speculated to be candidate functional genes related to fungus AF2 degrading PFOA.In conclusion,this work obtained two PFOA-degrading fungi for the first time,of which fungus AF2 was the dominant strain for degrading PFOA.PFOA oxidative stress test showed that fungus AF2 had higher PFOA tolerance.These results indicated that fungus AF2 is a microbial strain with better potential to degrade PFOA.At the same time,transcriptome sequencing of fungi AF2 at two kinds of fermentation conditions was carried out,and 16 candidate genes related to PFOA degradation were obtained by comparative transcriptomics analysis and gene function annotation.This study accumulated germplasm resources for microbial degradation of PFOA,and provided scientific data for elucidating the molecular mechanism of biodegradation and conversion of PFOA. |
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