Biological characteristics and genome analysis of Citrobacter freundii phage K1M

Bacteriophages that infect specific bacteria and cause their lysis are potentially useful for preventing and treating bacterial infections and controlling microbes in the environment. Citrobacter freundii is an opportunistic pathogen that is commonly present in the environment, food, animals, and human intestines. It also causes aquatic animal diseases in aquaculture. In this study, using Citrobacter freundii as the target host, a novel lytic phage, vB_CfrS_K1M (K1M), was isolated. Morphologically, K1M is a long-tailed phage with a head diameter of 68 ± 2 nm and a tail length of 130 ± 2 nm. The phage encodes a polysaccharide depolymerase and demonstrates stable biological activity. The genome of K1M is 47,995 bp in length, with 45.12% G + C content and 97 putative open reading frames (ORFs), only 36 of which encode proteins. The results of phylogenetic analysis based on TerL sequences suggest that K1M represents a new viral genus, for which we propose the name "Fredivirus".