Screening,Isolation,Biological Characteristics Analysis Of Bacteriophages In Sludge And Their Research On Sludge Lysis

As a commonly used sewage treatment process in China,the activated sludge method has a high removal efficiency of pollutants,but with the gradual increase in the amount of sewage in the process of urbanization,the amount of excess sludge also increases,and it is necessary to carry out the corresponding harmless and reduction treatment.Common sludge treatment methods include incineration,landfill,and comprehensive utilization.However,the incineration method has high treatment costs and will generate harmful gases during the incineration process;the landfill method is limited by land resources and may have an impact on local groundwater.The common industrial sludge fermentation method is a technology with a high sludge utilization rate,large reduction range,and methane production,but generally requires pretreatment by lysis technology.Compared with physical and chemical lysis,biological lysis has lower operating costs,simpler operation,and no secondary pollution.However,the research on biological lysis mainly focuses on bacteria and fungi.Less research has been done on purification and used for sludge lysis.The phages in the sludge have high abundance and diversity.In this paper,the dominant strains in the sludge and the phages used as hosts were screened and isolated.The phages'biological characteristics and their lysis of the sludge were analyzed.The main research results are as follows:(1)A strain of Escherichia fergusonii A23(referred to as A23,Genbank accession number:SUB10872183)and phage EP23(referred to as EP23 for short,Genbank accession number:SUB10871770)were isolated from the sludge.The colonies of A23 were yellowish,round and concave.The bacteria were oval and had long flagella.EP23 has an icosahedral head and a 77 nm tail with a head diameter of about 73 nm.It belongs to the Myoviridae and is highly specific to host bacteria.The plaque size formed by EP23 on the plate was 2 mm,and the optimal multiplicity of infection was 0.001.The lysis cycle of EP23 is about 2h,including the incubation period of 15min and the burst period of 60min,and the average burst volume is57PFU/cell.The activity of EP23 remained relatively stable in the range of p H 6-10and temperature 20-50?.Host bacteria are common in the environment and EP23 has good acid-base and heat tolerance,making EP23 a wider range of application scenarios.(2)Through the whole gene sequencing of bacteriophage EP23,its gene function was predicted,and a phylogenetic tree was constructed.The results showed that the total genome length of bacteriophage EP23 was 39321bp,the GC content was49.64%,and no resistance gene was found.There are 37 predicted genes,of which 29are compared to the Uni Prot KB/Swiss-Prot database.According to their functions,they can be divided into transcription,DNA modification,host cleavage,structural proteins,and DNA packaging.The other eight are hypothetical proteins.(3)Bacteriophage EP23 samples with different titers were added to the sludge,and the changes in COD,TN,protein,polysaccharide,VSS,CST and SV₃₀ in the sludge supernatant were observed.The results showed that the phage with a high titer had a better lysis effect on sludge than the phage with a low titer.The content of COD,TN,protein and polysaccharide in the supernatant of sludge fed with high titer phage increased by 54.0%,33.6%,55.1%and 26.1%,respectively.The content of VSS,CST and SV₃₀ decreased by 3.8%,9.3%,7.0%,respectively.The sludge floc gap increased,and the average floc gap size increased from 8.0?m before treatment to 18.3?m after treatment.The principle of phage lysis of sludge is that the enzymes such as Endolysin,Holin and Spanin produced by bacteriophages can lysis the host bacteria in the sludge.An in-depth study of the biological characteristics of phage is to explore the effect on sludge lysis.Attempt to explain the lysis phenomenon of phage from the perspective of genomics.It provides theoretical guidance for the application of bacteriophage and also provides a new attempt for biological lysis,which has certain reference significance for low-cost resource sludge.