Biological Characteristics And Genome Analysis Of Two Marine Bacteriophages

Objective and methods: Aeromonas hydrophila and Vibrio algolytica can infect a variety of aquatic animals and cause a large number of death,causing serious economic losses to the aquaculture industry,and they are also the main pathogenic bacteria of gastroenteritis and food poisoning.Phage therapy can be one of the effective methods to control bacterial infection.In this research,we studied the biological characteristics of an Aeromonas hydrophila phage and a Vibrio alginolyticus through observing their morphology,determining their host spectrum,MOI,one-step growth curve,and measuring their tolerance to temperature,p H,and Na Cl.And we analyzed the whole genomes through sequence alignment,ORF annotation,analysis and alignment,phylogenetic tree construction,Phage Term termini analysis to understand their genetic characteristics at the molecular level.Results: In this study,a lytic Aeromonas hydrophila phage X552 and a lytic Vibrio alginolyticus phage X194 were isolated from wholesale market sewage.Transmission electron microscope results showed that both phages belonged to Siphoviridae.X552 and X194 were relatively host specific.The MOI for both X552 and X194 was 0.1.The one-step growth curve showed that X552 had 20-min incubation period,70-min lysis period and the 22 PFU lysis amount;X194 had less than 10-min incubation period,80-min lysis period and 159 PFU lysis amount.Both X552 and X194 had a good capability to tolerant a range of temperature and Na Cl.X552 had a good capability to tolerant a range of p H.The genome of X552 wa s a linear ds DNA of 59685 bp in length,with a(G+C)content of 60.0%(NCBI Genbank accession number is MW978786).The results of RAST annotation showed that there were no t RNA and 74 ORFs in the X552 genome,of which 25 encoded functional proteins and 49 encoded hypothetical proteins.The genome sequence of X552 was compared with the 6 phages in the NCBI database,the identity was 75.22%-76.32%,and the corresponding query cover was 0%-8%,indicating that the homology between X552 and other phages was very low.The phylogenetic tree based on major capsid protein showed that X552 was in an independent branch and it might be a new genus of Siphoviridae.Phage Term termini analysis showed that X552 had 12 bp cohesive ends starting from 44714 bp of the positive strand,and used the cos 5’ packaging mechanism.The genome of X194 was a linear ds DNA of 73099 bp in length,with a(G+C)content of 38.5%(NCBI Genbank accession number is MZ447858).The results of RAST annotation showed that there were 5t RNA and 110 ORFs in the X194 genome,of which 17 encoded functional proteins and 93 encoded hypothetical proteins.The genome sequence of X194 was compared with the 7 phages in the NCBI database,the identity was 70.51%-97.65%,and the corresponding query cover was0%-2%,indicating that the homology between X194 and other phages was very low.The phylogenetic tree based on major capsid protein showed that X194 was in an independent branch and it might be a new genus of Siphoviridae.Phage Term termini analysis showed that X194 had588 bp direct terminal repeats starting from 57920 bp of the positive strand,and used the DTR packaging mechanism.Conclusions: In this study,two novel phages,X552 and X194,were isolated and identified.And their biological characteristics,genome sequencing and bioinformatics analysis were carried out.These two phages have good biological characteristics and neither virulence factors nor drug resistance genes in their genomes,so they have the potential to be applied in clinical treatment.This study provides a theoretical basis for phage therapy to treat bacterial infections.