Monitoring Microbial Diversity of Biofilms in Domestic Distribution Systems Using an in Situ Device

Biofilms in drinking water systems hosting diverse microbial communities are potential sources of opportunistic pathogens and taste/odour complaints. Domestic distribution networks are especially prone to biofilm formation due to high surface-to-volume ratio, elevated ambient temperature and intermittent use. Bacterial community diversity and determinants of community structure were investigated in two buildings using a purpose-designed in situ device containing stainless steel and polypropylene coupons and an online biofilm sensor. Next generation sequencing and scanning electron microscopy revealed increasing diversity and complexity over time. Initial biofilms were dominated by Proteobacteria (86–99%, primarily Burkholderiales and Sphingomonadales, core genera Aquabacterium and Blastomonas in month 1, and Rhizobiales in month 3), with an increasing ratio of Actinbacteriota (51–65%, mainly Corynebacteriales) and Bacteroidota (3–5%) by month 6. The impact of the sampling location was secondary to biofilm age in determining microbial diversity, and within-building variation was comparable to differences between facilities. The coupon material had a negligible effect on community structure. Real-time monitoring by online sensors did not yield interpretable data. Important nosocomial pathogens (Mycobacterium, Legionella, Methylobacterium, Bosea) were detected in the biofilm samples that were absent in bulk water, implying that water monitoring alone is not sufficient for estimating the risk of water-related pathogens.