 Abstract viruses are the most abundant microbial guild on the planet, and they can have a significant impact on microbial communities and ecosystem services. In engineered environments such as landfills, viruses are understudied and their interactions with hosts remain unclear. This study examines these interactions by analysing host CISPR spacer sequences against viral protospacer sequences from a municipal landfill over two years. The results show that viruses make up approximately for percent of the unassembled reads and assembled base pairs. Additionally, 458 unique virus host connections were identified, indicating that some viruses are not as host-specific as previously thought. Furthermore, for viruses were found to infect multiple phyla, suggesting that some viruses may be more widespread than previously believed. Finally, the study also discovered a virus encoding a CISPR array with 187 spaces, the longest virally encoded CISPR array ever reported. These findings suggest that viruses play a much larger role in the ecology of engineered systems than previously thought. This article was offered by Nikhil A. George and Laura A. Huck. We are article.tv, links in the description below.