Phage biocontrol in water treatment and reuse systems: a nascent field with significant innovation opportunities.

While the use of phages in the food and biomedical sectors occurs commercially, their application in the water sector is less common and is typically demonstrated at a lower technological readiness level. This is so despite the potential that phages have to enhance the control of problematic bacteria (including pathogens) and protect infrastructure within the water sector. Fulfilling the great potential of this nascent field requires more research and development. Here, we highlight innovation opportunities and discern critical knowledge gaps and research needs to facilitate the use of phages as precise biocontrol agents in the water sector. First, while the advent of sequencing technologies made it easier to identify bacterial communities and understand their functional roles, identifying and cultivating the appropriate phages that can be effective against the bacterial target requires more research. The large volumes of water to be spiked with phages also require optimizing the phage biocontrol strategy, minimizing the associated costs and enhancing scaling up. In addition, bacterial hosts may gain phage resistance after long-term exposure, which is common in most water-engineered systems, and strategies to minimize or delay resistance must be considered. In this opinion, we provide an overview of pertinent literature and bioinformatic tools that help identify appropriate bacterial hosts and phages for water systems applications. We then discuss strategies that can aid in prolonging the efficacy and enhancing the feasibility of phage biocontrol approaches.