Isolation And Application Of Cellulose-Degrading Exoelectrogen From Giant Panda Gut

With the development of economy and society,energy demand continues to grow.Energy resources and environmental issues are prominent increasingly.Accelerating the development and utilization of renewable energy is an inevitable choice to cope with increasingly severe energy and environmental problems.This thesis is focused on the screening and application of cellulose-degrading exoelectrogen from giant panda gut,and the following studies were carried out.1.Firstly,taking gut microbiota of giant panda as the research object,cellulose-degrading bacteria were enriched by inoculating feces from giant panda in0.25%paper(w/v)liquid medium.Six bacterial isolates were found on solid media.Then these six isolates were examined on cellulose/hemicellulose as sole carbon source in MFCs.The results demonstrated that the isolate named LZ-P1 exhibited the strongest electricity-generating abilities using cellulose as substrate among isolated strains.16S rRNA gene sequence of LZ-P1 revealed 99%homology with the genus Cellulomonas.Electricity generation of LZ-P1 was further analyzed using the CMC/microcrystaline cellulose/xylan/arabinose as substrate in anode.There was a rapid increase in voltage output over time.2.Although there are large amount of studies on cellulose-degrading bacteria isolated from gut of giant panda,the research on their extracellualr electron transfer(EET)is limited.To unveil mechanisms for simoutaneously electricity-generating and cellulose-degrading,genomic analyses of LZ-P1 were performed.In LZ-P1 genome,the discovery of genes encoding cellulose/hemicellulose degrading enzymes would benefit bioenergy production,for which cellulose/hemicellulose must be rapidly deconstructed and saccarified using enzymes.Furthermore,homologs of proteins that function in EET pathways components were also observed in the LZ-P1 genome.By characterizing pathways and genes empolyed in bacterial breakdown of cellulose/hemicellulose and electricity generation,we can see that LZ-P1 has the potential to PRW degradation and energy recovery.This is consistent with previous phenotypic experiments.3.Thirdly,to further dissect the mechanisms for electricity generation and cellulose degradation,proteomes of mono-carbon cultures(glucose or cellulose alone)were collected and prepared.Most of the proteomics analysis correlated with the genome data.Enzymes related to cellulose and hemicellulose degradation,inclucing endoglucanases,?-glucosidases and endoxylanases were up-regulated in cellulose and hemicellulose degradation.The results showed that the composition of proteins from LZ-P1 differed significantly between the two media.Comparing the protein expressions in open-circuit and out-circuit,proteins related to NADH-quinone oxidoreductase,riboflavin biosynthesis protein and cytochrome C oxidase were up-regulated significantly in open-circuit.Present fuel cell experiments show that Cellulomonas strain LZ-P1,which is considered to be important for gut diet metabolism and nutrition exchange for giant panda.4.Lastly,to evaluate the abilities of strain LZ-P1 in paper recycling wastewater(PRW)treatment,we investigated the power generation of LZ-P1 with wastewater.Performances on different original COD concentrations and pH of PRW showed that the maximum current density(44.05 mW/m~2)was obtained in 900 mg/L COD and pH8 PRW.COD removal was 60.9%in 72 h.These results demonstrate that PRW can be effectively treated and energy can be partly recovered using strain LZ-P1 mediated MFCs.The results obtained in this thesis will enhance our understanding of the roles of giant panda gut microbiota in its food digestion and nutrient metabolism,and provide valuable bacterial resource for the application of giant panda gut microbiota in the future.