Marine oxygen minimum zones (OMZs) are hot spots for microbial-driven matter and energy transformations, but the dynamics of virus–host interactions at these sites are poorly understood. In this study, Roux et al. used a combination of metagenomics and single-cell amplified genome (SAG) sequencing to investigate the viruses that infect the uncultivated sulphur-oxidizing SUP05 bacteria in an OMZ off the coast of western Canada. From a collection of 127 SAGs, they discovered five novel viral genera and estimated that approximately one-third of SUP05 are infected by one virus, although cells infected with several viruses were also detected. By examining 3 years of metagenomic data, they found that SUP05 viruses are endemic to this OMZ and are stable over time. Interestingly, the presence of a virus-encoded dissimilatory sulphite reductase suggests that these viruses probably influence bacterial sulphur metabolism, and thereby contribute to the biogeochemistry of OMZs.