| Chromate [Cr（Ⅵ）] and p-nitrophenol（PNP）are most commonly used industrial materials and often occur as pollutants in chemical industrial wastewater,which may cause seriously health and environmental problems due to their toxicity,mutagenicity and carcinogenesis.The Xigu district of Lanzhou city is located in the upper reaches of the Yellow River,which is the largest area of heavy industry in northwest China.This region was polluted by various heavy metals and organic compounds throughout the year.The communities of this region exhibit a notable ability to resist heavy metals and organic compounds.However,isolation and screening of strains for Cr（Ⅵ）reduction and PNP degradation of this area are still scarce.In order to better exploit the microorganism resources for Cr（Ⅵ）reduction and PNP degradation in this area,we collected soil samples along an effluent discharging canal.The successive enrichment method was employed to screen strains for Cr（Ⅵ）reduction and PNP degradation.In this study,we have elucidated the mechanism for the detoxification of Cr（Ⅵ）by a dominant strain,investigated the characterization of a PNP-degrading strain and tested its abilities for simultaneous current generation and PNP degradation in microbial fuel cell（MFC）.We also developed a novel portable biosensor system for in situ real-time monitoring of PNP.Finally,we tested the abilities of two Cr（Ⅵ）reduction strains and their co-cultures in MFC for removal COD and Cr（Ⅵ）in anode and cathode,respectively.The main results of this study are as follows:1.We have obtained 43 strains for Cr（Ⅵ）reduction or PNP degradation using three different ways,which belong to 16 genera.These genera are comprised of Streptomyces,Nocardiopsis,Nocardia,Cellulosimicrobium,Gordonia,Achromobacter,Pseudomonas,Brachybacterium,Rhodococcus,Arthrobacter,Leucobacter,Enterococcus,Lysinibacillus,Bacillus,Corynebacterium and Alcaligenes,and 11 genera among them belong to Actinobacteria.These results showed that actinomycetes may be the dominant groups in heavy metals and organic compounds polluted areas.2.Among Cr（Ⅵ）-reducing strains,a strain named LZ-26-1 which is closely related to Streptomyces violaceoruber（AB184174）demonstrated a notable ability of Cr（Ⅵ）reduction.It could reduce 92.86% of the 0.6 m M Cr（Ⅵ）to trivalent chromium [Cr（Ⅲ）] in SC liquid medium in 144 hours.The optimum temperature and p H were 28℃ and 7.0 for Cr（Ⅵ）reduction.TEM images and EDX analysis showed that chromium was precipitated inside the cells.In resting cells and crude chromate reductase assays,strain LZ-26-1’s Cr（Ⅵ）reduction was stimulated when NADPH was used as an electron donor,and Cd2+ treatment inhibited Cr（Ⅵ）reduction.Furthermore,a thioredoxin operon,which consists of three genes encoding a thioredoxin（Trx A）,thioredoxin reductase（NADPH）（Trx B）and a possible membrane protein（mem P）,was upregulated by Cr（Ⅵ）treatment.These results suggested that LZ-26-1 might utilize a thioredoxin pathway to reduce Cr（Ⅵ）.3.Among PNP-degrading strains,a strain named LZU-3 which is closely related to Pseudomonas monteilii（AF064458）demonstrated a notable ability of PNP degradation.The optimum PNP-degrading parameters of strain LZU-3 were as follows: inoculum amount of 10%（v/v）,p H 8.0,temperature 30 °C and supplemented with 50 μM FeSO4.7H2O in MS medium.The strain can also resist high concentrations of Na Cl and various metal ions.The co-substrates of pyruvate,acetate,lactate,glucose,mannitol,glycine and asparagine can promote PNP degradation,among them,asparagine showed a notable ability of enhancing PNP degradation.In the MFC experiments,the strain LZU-3 can simultaneously generate current and degrade PNP under aerobic conditions.The aeration can increase the maximum voltage（189 m V）and the PNP degradation rate(20 mg l-1 h-1)of the MFC,but it decrease the columbic efficiency.The strain can generate current at the PNP concentration within 300 mg l-1.The cyclic voltammetry（CV）analysis and SEM images showed that the electron transfer mechanism of strain LZU-3 was direct contact transfer via attaching to the electrodes.Pyruavate,as a co-substrate,which could promote voltage generation but decreased PNP degradation in the MFC.The riboflavin had no obvious promoting effect on the current generation of strain LZU-3.In this study,an aerobic PNP-degrading strain was firstly used in an aerobic anode MFC for simultaneous current generation and PNP degradation,which provide an example for using other aerobic or facultative anaerobic strains in MFCs.4.According to above results,a portable biosensor for PNP based on an aerobic anode MFC was designed.The biosensor employed strain LZU-3 as sensing element and PNP as sole substrate.The biosensor exhibits an excellent stability and accuracy for PNP detection in real wastewater.The study provide a rapid and effective way for monitoring of toxic and recalcitrant pollutants in environmental analysis.5.Among Cr（Ⅵ）-reducing and PNP-resisting strains,two strains named LZU-26 and LZU-47-1 which are closely related to Cellulosimicrobium cellulans（X83808）and Corynebacterium vitaeruminis（X84680）,respectively,demonstrated a notable ability of Cr（Ⅵ）reduction and current generation in MFC using molasses wastewater as substrate.In this study,we inoculated with strain LZU-26,LZU-47-1 and co-cultures of them in MFCs as anode and cathode biocatalysts,respectively.The MFC can simultaneously removal COD in the anode and removal Cr（Ⅵ）in the cathode.The results showed that the co-cultures can promote current generation and COD removal.When the COD concentration in the range of 400-8000 mg l-1,the co-cultures could produce current in the MFC,and the optimum COD concentration for current generation was 800 mg l-1.When the Cr（Ⅵ）was employed as cathode electron accepter,the co-cultures as anode and cathode biocatalysts simultaneously,the Cr（Ⅵ）concentrations in the range of 10-20 mg l-1,the COD removal rate,current density and Cr（Ⅵ）removal rate of the MFC increased with the Cr（Ⅵ）concentration.This study use MFC to remove COD in the anode and remove Cr（Ⅵ）in the cathode,providing an effective way for combined pollution treatment. |
