Development Of Microfluidic Assay For Bacteria Chemotaxis And Its Application In Sewage Treatment

Chemotaxis is the ability of organisms to sense gradients in their chemical environment and adjust their motile behavior accordingly.Bacteria,for example,are often able to measure chemical gradients and move towards higher concentrations of a favorable chemical or lower concentrations of an unfavorable one.This mechanism is a nature of microorganisms to adapt to the environmental changes.The research of chemotaxis is of great significance in utilizing of bacteria for solving environment problems,including pathogen infection,environmental governance and microbial industrial projects.Compared to traditional detection methods,microfluidic assay has an accurate control over bacterial microenvironment,and has a higher sensitivity.Microfluidic technology offers the possibility to overcome these limitations by enabling generation of highly controlled chemical gradients and measurements of the bacterial response at high spatiotemporal resolution.In this paper,I have designed a microfluidic chip which used for the reaction device.In this system,the fluorescence microscope is observation equipment and CCD is recording device.The gradient of the chemical will form in the channel of the chip,for detecting the bacterial chemotaxis.The microfluidic system was used to analysis the chemotaxis of bacteria.The factors such as temperature,light intensity,the type of chemical and the concentration of chemical were explored by this system.Furthermore,I selected three species of bacteria in activated sludge to detect the chemotaxis by microfluidic chip.By comparing the Chemotaxis Migration Coefficient(CMC)of three species of bacteria,determine the chemotactic sensitivity.This application provided a new method for screening the dominant species of activated sludge.Comparing the diffusion of the fluorescent agent at different flow rates,the flow rate of the chemotactic / buffer solution was 80 ?L / h,and the flow rate of the bacteria was 40 ?L / h(the flow rate was 1.24 in the channel).This form the optimum flow rate for the chemotaxis experiment.The results showed that the responses of E.coli to different chemotaxis was different.The mobile trend of E.coli to aspartic acid was higher than the mobile trend to serine or leucine.This is mainly due to the differences in the induction of the agent.In addition,the response of E.coli to different concentrations of chemotaxis was also different.The response of the chemotaxis will increases with the increase of the concentration.The increase rate becomes slower and tends to be stable after achieve a certain value.The chemotactic receptors on the cell membrane can perceive the number of molecules and to response to the mobile signal.The membrane receptor will be saturated when the number of molecules increased to a certain value,the mobile signal will no longer increased.The response of different bacteria to homologous chemotactic agents were also different.The E.coli ATCC25922 and theflagellinfree E.coli BL21 was tested at the same condition.The experiment results showed that the migration of the flagellin was similar to E.coli ATCC25922,different types of bacterial have different response.I choose Pseudomonas aeruginosa,Proteus vulgaris and Eosinophilic bacteria which were a large part of the activated sludge as the detection object,and the aspartic acid as the chemotactic agent.According to the CPC and CMC obtained from the experiments,the CMC of chemotaxis of the Pseudomonas aeruginosa to aspartic acid was the largest.The Pseudomonas aeruginosa have the most obvious movement trend.Bacteria will move to the region with high concentration of aspartic acid and used it for degradation at first.In this way,the dominant strains couled be acreened from several different species of bacteria according to the chemotaxis.The dominant strains has a strong chemotaxis and can achieve greater degradation to the pollutants in the biological treatment of sewage.