Temperate Stutzerimonas Phage Encoding Toxin-Antitoxin System Genes Represents a Novel Genus

Stutzerimonas have been extensively studied due to their remarkable metabolic and physiological diversity.However,research on its phages is currently limited.In this study,we isolated a novel double-stranded DNA(dsDNA)phage,vB_SstM-PG1,from the marine environment that infects Stutzerimonas stutzeri G1.Its dsDNA genome is 37204 bp long with a G/C content of 64.14%and encodes 54 open reading frames.The phage possesses a tail packaging structure that is different from known Stutzerimonas stutzeri phages and exhibits structural protein characteristics similar to those of temperate phages.In addition,two genes of toxin-antitoxin system,including YdaS_antitoxin and HEPN_SAV_6107,were found in the vB_SstM-PG1 genome and play important roles in regulating host growth and metabolism.With phylogenetic tree and comparative genomic analysis,it has been determined that vB_SstM-PG1 is not closely related to any phages previously identified in the GenBank database.Instead,it has a connection with enigmatic,uncultured viruses.Specifically,the vB_SstM-PG1 virus exhibits an average nucleotide identity of over 70%with six uncultivated viruses identified in the IMG/VR v4 database.This significant finding has resulted in the identification of a novel viral genus known as Metabovirus.

Transient carriage and low-level colonization of orally administrated lytic and temperate phages in the gut of mice

Many studies have shown the efficacy of phage therapy in reducing gastrointestinal pathogens.However,it is unclear whether phages can successfully colonize the gut when administered in an adequate amount for a long time.About 1×10^(8)PFU/mL of purified lytic phage PA13076 or temperate phage BP96115 were fed daily to mice via drinking water over 31 days,to elucidate the distribution of phages in the gastrointestinal tract.At day 16 and 31,six different segments of the gastrointestinal tract with their contents,including stomach,duodenum,jejunum,ileum,cecum,colon,and fresh feces,were aseptically collected.The phage titers were determined using the double-layered plate method with S.Enteritidis ATCC 13076 or S.Pullorum SPu-109 used as host cells.The results indicated that a small portion of administered phages survived exposure to gastric acid and entered the intestinal tract.The prevalence of phages in the gastrointestinal tract was lower than 1%of the primary phage count.Highest phage titers were detected in the cecum with 10^(4)~10^(5)PFU/g,and most of the phages were eliminated from the body via feces with 10^(6)PFU/g.On day 16 and day 31,the same level of phage titers in different segments of the gastrointestinal tract indicated that the colonization of phages had reached saturation at day 16.These results demonstrate transient phage carriage and low-level colonization of orally administrated lytic and temperate gut phages in mice.