Although bacteriophages are central entities in bacterial ecology and population dynamics, there is currently no literature on the genomes of bacteriophages isolated from groundwater. Using a collection of bacterial isolates from an aquifer as hosts, this study isolated, sequenced and characterised two bacteriophages native to the groundwater reservoir. Host phylogenetic analyses revealed that the phages targeted B. mycoides and a novel Pseudomonas species. these results suggest that both bacteriophages represent new genera, highlighting that groundwater reservoirs, and probably other subsurface environments as well, are underexplored biotopes in terms of the presence and ecology of bacteriophages. Despite metagenomics revealing that groundwater reservoirs harbour complex bacterial communities that are closely associated with biogeochemical cycling, much remains uncharted about their microbial ecology 1. In this context, it could be argued that bacteriophages (phages) have been studied to an even lesser extent, but they are generally considered to play a fundamental role in shaping bacterial communities and consequently influencing biogeochemical cycling 2, 3. While viruses (including phages) only constitute 0.04% of the earth's biomass 4 , they are widely regarded to constitute the largest and most diverse family of biological entities 5. Thus, mapping out their taxonomy, distribution and ecological role is a daunting task. Currently, there are no genome sequences of phages, isolated from groundwater systems, despite descriptions of phage abundances and viromes in these systems 6,7. This study isolated, sequenced and characterised two novel phages from a groundwater reservoir. To the authors' knowledge, this is the first report on groundwater phages that includes their sequenced genome and phylogenomic affiliation. The aim of the present study was to describe the first isolated groundwater bacteriophages that target actual bacterial isolates from the groundwater reservoir through isolation, genome sequencing, bioinformatics and protein characterisation. Predator-prey pairs are of relevance not only in the study of environmental microbiology, including the food webs of groundwater aquifers, but also in the context of bioaugmentation for purification of contaminated groundwater, where knowledge of indigenous enemies is crucial to the survival of introduced degrader bacteria. Results and discussion Phage isolation and phage host identification. Using a collection of natural bacterial groundwater isolates as hosts, two phages-Anath (Genbank accession MG983742.1) and Lana (Genbank accession MK473373.1)-were successfully obtained and their hosts identified as Bacillus mycoides and Pseudomonas sp., respectively, by means of the publicly available online tool for strain identification Type (Strain) Genome Server (TYGS) (https ://www.tygs.dsmz.de) 8. Besides being the first sequenced groundwater phages, this is also the