Cell Size Homeostasis Mechanism Of Escherichia Coli Under Anaerobic Environment

Bacterial cell size regulation mechanism is a basic problem in life sciences.It is just because of its precise control mechanism on size that it can achieve physiological homeostasis.This homeostasis maintains the distribution of the two types of cells that grow and divide into the cell cycle remains stable;on the contrary,if there is no effective size control mechanism,the changes in cell size distribution will span multiple orders of magnitude.In fact,the size change is only about twice that between new cells and dividing cells.Escherichia coli(E.coli)is a typical model microorganism,which is a facultative anaerobe and is also widely distributed in the human intestine.The inside of the intestine is actually an anaerobic environment,so the single-cell experimental data collected under anaerobic environment in this study is of great practical significance.And this provides technical support and reference data for subsequent studies on bacterial physiology,including drug resistance.Furthermore,it provides theoretical support for industrial production and medical treatment and other fields.This study employed microfluidic chip and high-resolution microscope time-lapse photography technology,which can ensure the long-term stable growth of bacteria.The image analysis software developed by our research group is used to process and analyze the image data.Then obtain single-cell physiological parameters such as single-cell cell size and single-cell growth rate,which provide sufficient data support for model establishment.In addition,in order to ensure a strictly anaerobic environment during cultivation,a special sealed anaerobic box is used to hold the microfluidic chip and liquid culture medium in a constantly replenished anaerobic mixed gas atmosphere to achieve a long-term stable anaerobic environment.The first step of this study is constructing the anaerobic microenvironment required for real-time observation of single cells.Then the reliability and stability of the strict anaerobic environment are proved from the gas atmosphere and cytological level.Furthermore,a complete experimental system and process are used to realize the continuous cultivation and monitoring of facultative anaerobic bacterial whole anaerobic-aerobic process.During the anaerobic-aerobic"traceless"switching,before and after the adjustment of the cellular physiological state,it is demonstrated by the perspective of cell size and growth kinetics data that steady-state growth was achieved during both anaerobic and aerobic culture.Based on this steady-state growth,comparing the various physiological parameters of anaerobic and aerobic,the experimental results are basically correspond with expectations,that is,the growth rate and size of bacteria under anaerobic culture are reduced compared with that under aerobic culture.After analysing the dat,it is found that there is an over-regulation mechanism when the physiological state of the cell is switching.As far as I know,this phenomenon has not been reported in studies related to cell size regulation.Analyzing the single-cell size data,the results show that the size regulation of facultative anaerobes under aerobic conditions almost perfectly correspond with the"adder"model,and the slope of the final-initial length(L_F-L_I)linear equation is 1;however,under anaerobic conditions,the slope of the L_F-L_I linear equation is obviously less than 1,and it's about 0.8.Since this study is a continuous anaerobic-aerobic experiment,the microscope time-lapse shooting process is not interrupted;and the same image analysis method is applied and the data are processed at the same batch,errors caused by experimental conditions and analysis methods can be eliminated.It strongly proves the existence of this"sizer-like adder"(partial filter adder)phenomenon.In addition,the comparative analysis of anaerobic and aerobic experimental data at different temperatures questions the simple correspondence between size regulation and growth rate,and also questions one of the classic bacterial growth laws that temperature has no effect on bacterial cell size.