Study Of The Structure Evolution And Recovery Process Of Electroactive Biofilm Under Long-term Starvation

Bioelectrochemical System(BES)is a technology that converts the chemical energy of organic matter into electrical energy through the catalytic reaction of microorganisms.Electroactive biofilm(EAB),as the core of BES,plays an important role in substrate metabolism and Extracellular electron transport(EET).The strength of the electric current is related to the bioelectrochemical characteristics of the EAB which is attached to the anode.Biofilms are susceptible to nutrient deficiency in the natural environment.Due to the complex microbial communities and protective Extracellular Polymeric Substances(EPS),biofilms can have strong adaptability and tolerance.The substrate is the source of electrons and energy in EAB.The continuous supply of the substrates maintains the normal operation of BES.However,in practice,the supply of substrates may be interrupted by equipment failure or technical maintenance.The lack of substrate will affect the activity and structure of EAB,and further affect the normal operation of BES.Herein,the anode biofilms were cultured on two different substrates,sodium acetate and glucose.The mature EAB was starved for 10 or 20 days without the supply of the substrate.The electrochemical activity,metabolic activity,morphology and structure of biofilms and the changes of EPS components in different starvation stages was evaluated.The recovery of EAB activity after starvation was explored.The mainly mechanism of starvation on the diversity of microbial communities in EAB was proposed.The main findings are as follows:(1)The change curve of the current density of electricity generated during the formation of EAB over time was recorded by electrochemical workstation.It was found that sodium acetate can induce the enrichment of electroactive microorganisms more effectively than glucose.The stable current density of sodium acetate EAB is higher.The biofilm recovered after 10 days of starvation has irreversibly reduced its electricity production performance.As to the biofilm recovered after 20 days of starvation,the electricity generation capacity of sodium acetate EAB can basically reach the normal level before starvation.The electricity generation current density of glucose EAB can be restored to 85% of the original.(2)The biofilm was observed and hierarchically analyzed with high resolution laser confocal microscopy(CLSM).It was found that the mature EAB showed a double-layer biofilm structure with live cells on the outer layer and dead cells on the inner layer.Starvation treatment will reduce the activity of EAB.Due to the coexistence of electroactive microorganisms and fermenting microorganisms,glucose EAB has a stronger ability to resist hunger.In the biofilm recovered after 10 days of starvation,the cell activity of the inner and outer layers decreased,and the dense structure of the inner layer of the biofilm increased the material transmission resistance and reduced the EET efficiency.In the biofilm recovered after 20 days of starvation,the cell activity significantly increased,the density of the inner biofilm decreased,and the biofilm appeared aging and shedding.(3)The change of the various components of EPS were analyzed.It was found that starvation treatment caused the decreasing of the polysaccharide and protein content of EPS.Bacteria can metabolized some of EPS to maintain the structure and function of the biofilm.(4)The results of community structure analysis showed that starvation led to the increasing of the richness and diversity of the community.Geobacter was the dominant electroactive genus in sodium acetate EAB.Its relative abundance in the anode biofilm decreased with the increasing of starvation time.Its relative abundance increased after the substrate was restored.The synergistic interaction between fermenting bacteria and electroactive bacteria is beneficial for adapt to the harsh external environment.Thereby the biocatalytic ability of the anode biofilm was enhanced.This thesis aimed to improve the activity of EAB and the performance of BES.By studying the effect of substrate deletion on the activity and structure of EAB,it was clarified that the starvation can promote the aging and shedding of biofilms and is beneficial to the recovery of BES performance.The microbial mechanism of starvation treatment affecting the performance of BES was analyzed.The higher the abundance of the dominant electroactive bacteria,the more beneficial the operation of BES.The research results provide a theoretical basis for building a continuous and efficient EAB.