Symbiosis of a lytic bacteriophage and and characteristics of plague in .

Surveillance for animal plague was conducted in the plague focus of the Qinghai-Tibet Plateau from 2020 to 2023. A 22.89% positive rate of serum F1 antibody was detected in live-caught marmots, alongside a 43.40% incidence of isolation from marmot carcasses. Marmot carcasses infected with plague exhibited a significantly higher spleen-somatic index ( < 0.05). Twenty-one specific phages were isolated, among which one lytic phage (AKS2022HT87GU_phi) was isolated from the bone marrow of a marmot carcass (no. AKS2022HT87) and was found to be symbiotic with . Microscopy revealed the coexistence of lysed and non-lysed colonies of AKS2022HT87. Genome-wide analysis showed that certain strains of the AKS2022HT87 carried phage DNA fragments consistent with phage AKS2022HT87GU_phi. The rare symbiotic relationship between a lytic phage and observed was highlighted in this study, laying the basis for further exploring the relationship between and its bacteriophages.IMPORTANCEBacteriophages and host bacteria commonly coexist or in soil environments through complex and interdependent microbial interactions. However, recapitulating this symbiotic state remains challenging due to limited medium nutrients. In this work, the natural symbiosis between and specific phages has been discovered in a specimen. Epidemiological analysis presented the characteristics of the and specific phages in the area with a strong plague epidemic. Crucially, comparative genomics has been conducted to analyze the genetic changes in both the and phages over different periods, revealing the dynamic and evolving nature of their symbiosis. These are the critical steps to study the mechanism of the symbiosis.