The Effect Of Pili And Nanomaterials On The Extracellular Electron Transfer Of Geobacter Sulfurreducens

Certain microorganisms can reduce outer surface electron acceptors by a way named Extracellular Electron Transfer (EET). It plays an important role in the biogeochemical cycles of environments, bioelectrochemical systems and bioremediation. Geobacter sulfurreducens belong to Geobacteraceae. They are anaerobic bacteria and predominant below the surface. G.sulfurreducens strain PCA can oxidize organic compounds and couple the reduction of kinds of electron acceptors in the environment, which influences the formation of soil, the bioremediation process and also acts as a main rate limit step in microbial fuel cell.Strain PCA transports and dumps electrons out cell by EET, which needs the cooperation of different elements, such as c-type cytochromes, pili and even the mineral particles in the soil. In our study, we focus on the relationship between pili or nanomaterials and the EET. It is widely accepted that strain PCA needs pili to achieve EET. However, little is known about the function of pili during EET, not even the coding gene and translation start codon. So, firstly, we localized the pili gene and identified its translation start codon as ATG. Next, we expressed different pili with different compositions and structures in strain PCA and characterized their impact on the EET.Anode can act as a stable electron acceptor to accept electrons produced by electrigens. Anode modification can improve the efficiency of electrogenic bacteria to reduce the anode, which enhances the EET. In our study, we also synthesized Graphene/Hemin nanocomposite and applied it on the anode to accelerate the electron transfer at the interface between bacterial and electrode. The details as follows:(1)His-tagged the predicted PilA. After immunogold labeling with anti-his tag antibodies, we proved the his-tagged PilA can participate the construction of pili and then designated the gene GSU1496 as the pila. It was reported that prepilin had two isoforms that were long isoform and short isoform. However, according to our data, prepilin only had one form and translated from the single start codon of ATG.(2) Constructed strain PA, which expressed the pila gene of Pseudomonas aeruginosa strain PAO1. We proved that the expression of PAO1 pili on G.sulfurreducens did not affect the distribution of outer cellular c-type cytochromes but diminished the EET.(3) Identify the impact of single aromatic ammo acid among the five of the c-terminal of PilA on the pili mediated EET of G.sulfurreducens. Labeled the c-terminus of PilA with c-type cytochrome PpcA and tested the effect of increase the c-type cytochrome loading on the EET of G.sulfurreducens. Besides, G.sulfurreducens were also used to express different pili with distinct structures, which included the pili of Geobacter metallireducens, Geobacter uraniireducens, Pelobacter carbinolicus and the truncated pili of G.uraniireducens, and P.carbinolicus, and found the relation between the structure of pili and the efficiency of EET.(4) The OmcZ mutant of G.sulfurreducens cannot reduce anode to produce electricity continually. We synthesized Graphene/Hemin nanocomposite to mimic the c-type cytochrome and applied it on the anode. We found the decoration partially recovered the EET of OmcZ mutant and proved Graphene/Hemin nanocomposite can act as an effective anode modifier to improve the power production of microbial fuel cell.