Bioaccumulation of bacteriophages T4 and RB43 in Unionidae mollusks: a comparative analysis

The relevance of this study stems from the need to understand the role of bivalve mollusks as natural reservoirs of viral particles in aquatic ecosystems. The problem lies in the insufficient knowledge of the mechanisms behind the selective bioaccumulation of bacteriopha ges by mollusks and its ecological consequences. The aim of this work was a comparative study of the accumulation kinetics of bacteriophages T4 (genus Tequatrovirus) and RB43 (genus Pseudotevenvirus) in the freshwater mollusks Unio pictorum and Anodonta cygnea, and to identify the molecular basis for the differences in this process. During the experiments, a comparative analysis of the phage titer dynamics in the environment was conducted, revealing fundamentally different strategies in their interaction with the mollusk and the surrounding water. It was established that bacteriophage T4 actively replicates and is firmly sorbed within the mollusk, whereas RB43 demonstrates weak adhesion to the filtration apparatus and is subject to constant migration back into the environment. A correlation was found between these differences and the structure of their capsid proteins: T4 exposes 8.6 times more Ig-like domains (via the Hoc protein) than RB43 (via the Wac protein). This presumably determines the efficiency of binding to mollusk mucus mucin and, consequently, the retention within the mollusk’s body. The scientific significance of the work lies in discovering the dependence of bioaccumulation on the presence of specific Ig-like domains in the decorating proteins of phages, which expands the fundamental understanding of the evolution and ecological differentiation of bacterial viruses. The practical significance is related to the fact that phage RB43, unlike T4, is an efficient transducer of antibiotic resistance genes. The weak sorption of RB43 in mollusks and its constant migration could facilitate the widespread dissemination of resistance plasmids in aquatic environments. Prospects for further research involve studying the role of mollusks as an ecological niche that promotes the bacteriophage-mediated horizontal gene transfer between bacteria.