Biological Characteristics And Genomics Of Two Serratia Marcescens Phages

Serratia marcescens is a rod-shaped Gram-negative bacterium and a conditioned pathogen,which mainly causes iatrogenic infection.It can cause a variety of infectious diseases,such as pneumonia,meningitis and sepsis.In recent years,due to the extensive use of antibiotics,the isolation rate of drug-resistant S.marcescens is getting higher and higher,and more and more cases of outbreak and epidemic caused by drug-resistant strains are reported,which leads to more and more difficulties in clinical treatment of S.marcescens infection.This has forced many scholars to start looking for new alternatives to antibiotics.As a virus specializing in bacterial lysis,bacteriophage has strict host specificity.It can kill host bacteria without killing other normal bacteria.It is one of the good alternatives to antibiotics.In this study,using S.marcescens as host bacteria,two virulent bacteriophages were isolated from two different waste water samples,named vB_SmaA₂050H1 and vB_SmaM₂050HW.The morphological,biological,molecular genetics and genomics of these two bacteriophages were analyzed and studied.The morphological and genetic information of the bacteriophage is well understood,which will be helpful for the further study of the bacteriophage of S.marcescens.The results showed that the phage plaque of vB_SmaA₂050H1 was small and transparent with a diameter of about 1.23±0.29 mm.The phage plaques of vB_SmaM₂050HW was also small and transparent,slightly smaller than that of vB_SmaA₂050H1 with a diameter of about 0.82±0.24 mm.The results of transmission electron microscopy showed that the two bacteriophages belonged to Caudovirales.The head of the bacteriophage vB_SmaA₂050H1 was hexagonal,and the tail complex was composed of a wide,umbrella-shaped,fibrous and star-shaped structure.In morphological taxonomy,the bacteriophage belonged to the ViI-like family.The tail of phage vB_SmaM₂050HW is composed of a complex,umbrella-shaped,fibrous and stellate structure.According to Ackermann's classification and identification system,vB_SmaM₂050HW belongs to Myoviridae family.The one-step growth curve of the two bacteriophages showed that vB_SmaA₂050H1 had a latent period of 80 min.The burst size was approximately 966 plaque-forming units?pfu?per infected cell.vB_SmaM₂050HW had a latent period of 40 min.The burst size of vB_SmaM₂050HW was approximately 113 pfu per infected cell.The identification of host range showed that vB_SmaA₂050H1 infected 10 of 15 strains of S.marcescens,while vB_SmaM₂050HW lysed 12 strains.In this study,genomes of the two bacteriophages were sequenced by Hiseq2500 sequencer.Several bioinformatics tools were used to annotate the bacteriophage genes,and the genome sequences of the two S.marcescens phages were analyzed in detail.Sequence analysis revealed that phage vB_SmaA₂050H1 has a double-stranded DNA genome consisting of 159,631 bp,with a GC content of 51.96%,213 predicted ORFs,and two tRNAs genes,tRNA-Met?AUG?and tRNA-Cys?UGU?..Gene modular structure is mainly divided into structural gene,replication/recombination/repair gene,nucleotide metabolism gene,transcription/translation gene,DNA mature gene and other functional genes.The vB_SmaM₂050HW genome was 276,025 bp in length,with a GC content of 46.79%,363 predicted proteins,and one tRNA gene,tRNA-Tyr?UAC?.Phage vB_SmaM₂050HW gene modular structure is mainly divided into structural gene,replication/recombination gene,nucleic acid metabolism gene,transporter gene,DNA mature gene and other genes.By comparative genomics analysis,the bacteriophage vB_SmaA₂050H1 is a member of the ViI-like family,and vB_SmaM₂050HW is a novel bacteriophage.Preliminary study of phage receptors revealed that both phage receptors were exopolysaccharides and had a concentration-dependent adsorption capacity for exopolysaccharides.In summary,two virulent bacteriophages were isolated from different wastewater samples.By studying the phage plaque,transmission electron microscopy,host range determination and one-step growth curve of the two bacteriophages,the biological characteristics,host range and classification of the bacteriophages were analyzed.The genome sizes of vB_SmaA₂050H1 and vB_SmaM₂050HW were 159,631 bp and 276,025 bp,respectively.The genomes of vB_SmaA₂050H1 and vB_SmaM₂050HW contained 213 and 363 ORFs respectively.Genome sequence analysis showed that vB_SmaA₂050H1 is a member of ViI-like family,while vB_SmaM₂050HW was a novel virulent phage.These findings will provide a theoretical basis for the control and research of drug-resistant S.marcescens and the application of bacteriophages.