Diversity Of Potential Bacteria For PAHs-Cr(?) Remediation And Characterization Of Functional Bacteria

Co-contamination of heavy metals and organic pollutants is one of the most common situations in combined pollution.Chromium?Cr????and polycyclic aromatic hydrocarbons?PAHs?are teratogenic,carcinogenic and mutagenic.Studies suggested that PAHs and Cr???co-contamination exerted stronger deleterious effects on the environment,animals and plants.Bacteria,as the most abundant and sustainable resources in the environment,have shown enormous potential in heavy metals tolerance and PAHs degradation.Acquiring efficient and stable bacteria is the key to bacterial remediation.The innovation of sequencing technology has provided technical support for the in-depth study of bioinformatics,and the information of genome and metagenome databases has been continuously increasing.In this study,functional genes rhd and chrA were used as markers to analyze the diversity of potential bacteria for PAHs-Cr???remediation and the diversity of such functional genes in the environment by gene mining method.Bacteria that capable of PAHs-Cr???remediation?duo-functional bacteria?were obtained by functional validation under the guidance of gene mining.The remediation ability of duo-functional bacteria was characterized and optimized.Finally,the remediation mechanism for PAHs-Cr???was preliminarily explored from the transcriptional level of a strain.The conclusions of this study are as follows:?1?1196 genomes that carrying both rhd and chrA genes of the 42213 bacterial genomes in IMG/M were obtained from IMG/M befor 2017,which affiliated to 13 phyla,20 classes,58 orders,123 families,401 genera and 1164 species.Proteobacteria,Firmicutes,and Actinobacteria were the most abundant phyla.Moreover,most strains contain more than one functional gene.rhd and chrA genes are widely distributed in the environment.The taxonomic analysis of four metagenomes from different ecosystems showed that the distribution of the two functional genes was totally different.There are a large number of "uncultured/unclassified" genes in metagenomes which are not existed in genomes.Therefore,genomic and metagenomic mining method can be complementary to each other in this study.?2?Two novel duo-functional strains,Pseudarthrobacter phenanthrenivorans J015 and Croceicoccus naphthovorans PQ-2T,were identified and characterized according to genome-guided functional validation.This is the first time that duo-functional bacteria have been found in Pseudarthrobacter and Croceicoccus.J015 showed excellent ability in Phe-Cr???remediation.Phe?100 mg/L?can be completely degraded by J015 at 30 mg/L K2Cr2O7,and Cr???can be reduced simultaneously during the degradation process;Phe can still be degraded by JO 15 at 90 mg/L K₂Cr₂O₇,and about 70%of Phe can be degraded in 28 days;the cultural conditions for Phe-Cr???remediation by J015 were pH=6.0,30?,and 100 mg/L additional glucose.?3?The effect of Phe/Cr?VI?on the expression levels of chrA/rhd genes in the remediation process.Phe/Cr?VI?could up-regulate the expression of chrA/rhd gene at the early stage of culture?p<0.05?,and the stimulation effect of Phe on chrA gene was more obvious with the expression of chrA was up-regulated by more than 100 times;Cr???could inhibit the expression of rhd genes at the middle and late stage of culture,which was consistent with the results of corresponding remediation ability study.The mechanism under the phenomena still needs to be further studied.