Viral Hijacking and Metabolic Reprogramming in Candidatus Pelagibacter ubique: Ecological Consequences of Phage-Driven “Zombification” in the Global Ocean

Candidatus Pelagibacter ubique, a dominant member of the SAR11 clade, is among the most abundant heterotrophic organisms in the global ocean and plays a central role in marine carbon cycling. Despite possessing one of the smallest genomes of any free-living organism, SAR11 thrives in oligotrophic marine environments through extensive genome streamlining, efficient nutrient acquisition systems, and specialized metabolic adaptations. However, SAR11 populations are subject to persistent viral predation by pelagiphages, a diverse group of bacteriophages that influence microbial mortality, evolution, and nutrient turnover throughout the oceans. This review examines current understanding of SAR11 physiology, pelagiphage infection dynamics, and the ecological consequences of infection-induced metabolic reprogramming. Particular emphasis is placed on viral manipulation of host metabolism, auxiliary metabolic genes, host resource allocation, and the role of phage-mediated lysis in the marine viral shunt. The term “zombification” is used here as a conceptual analogy describing a transient physiological state in which infected cells may remain metabolically active while cellular functions become increasingly redirected toward viral replication. While aspects of this phenomenon have been observed in marine phage-host systems, several proposed mechanisms remain incompletely resolved in SAR11-pelagiphage interactions and require further experimental investigation. We further examine how viral turnover of SAR11 biomass contributes to dissolved organic matter recycling, nutrient redistribution, and the regulation of oceanic carbon sequestration. Finally, emerging genomic, transcriptomic, and imaging technologies are discussed as tools for resolving outstanding questions concerning host-virus interactions in marine ecosystems. Understanding how pelagiphages alter the physiology and ecological function of SAR11 populations provides important insight into one of the most widespread biological interactions in the global ocean and its potential consequences under changing climatic conditions.