Aquatic fungal intrusion increases microbial risk in premise plumbing system: Novel insights into water quality, bacterial community and function of pathogens

Fungi in drinking water pose a potential biohazard because treatment plants only partially remove them. The potential ecological impacts of viable fungi and fungal-derived organic matter entering premise plumbing systems remain uncertain. In this study, we established pipeline systems to examine the impact of fungi and fungal dissolved organic matter (DOM) on water quality, microbial stability, and function of pathogens. Under stagnant conditions, the accumulation of fungi and fungal DOM in the pipeline system caused the peaks of ammonia nitrogen and nitrite nitrogen concentrations to increase by factors of 3.0 and 6.5 times, respectively, compared to the Control group. In the presence of fungi and fungal DOM, the total cell count and adenosine triphosphate contents in drinking water initially increased, and then decreased over time, and bacterial utilization capacity for L‑serine and L-asparagine increased. Both fungi and fungal DOM altered the bacterial community structure in drinking water. Notably, the intrusion of fungi and fungal DOM increased the level of opportunistic pathogens, such as Pseudomonas mendocina, Phocaeicola plebeius, and Pseudomonas aeruginosa, in drinking water. Total nitrogen concentration showed significant positive correlations with the bacterial community. Our findings provide a scientific basis that can inform effective strategies for drinking water safety in response to sudden increase in fungal contaminations.