Daily Archives: June 22, 2015

Dominant Bacteria in Chloraminated Distribution System Biofilms

Gomez-Smith CK, LaPara TM, Hozalski RM. Sulfate Reducing Bacteria and Mycobacteria Dominate the Biofilm Communities in a Chloraminated Drinking Water Distribution System. Environmental Science and Technology. 2015 Jun 22.

The quantity and composition of bacterial biofilms growing on ten water mains from a full-scale chloraminated water distribution system were analyzed using real-time PCR targeting the 16S rRNA gene and next-generation, high-throughput Illumina sequencing. Water mains with corrosion tubercles supported the greatest amount of bacterial biomass (n = 25; geometric mean = 2.5 × 107 copies cm-2), which was significantly higher (P = 0.04) than cement-lined cast-iron mains (geometric mean = 2.0 × 106 copies cm-2). Despite spatial variation of community composition and bacterial abundance in water main biofilms, the communities on the interior main surfaces were surprisingly similar, containing a core group of operational taxonomic units (OTUs) assigned to only 17 different genera. Bacteria from the genus Mycobacterium dominated all communities at the main wall-bulk water interface (25% to 78% of the community), regardless of main age, estimated water age, main material, and the presence of corrosion products. Further sequencing of the mycobacterial heat shock protein (hsp65) provided species-level taxonomic resolution of mycobacteria. The two dominant Mycobacteria present, M. frederiksbergense (arithmetic mean = 85.7% of hsp65 sequences) and M. aurum (arithmetic mean = 6.5% of hsp65 sequences), are generally considered to be non-pathogenic. Two opportunistic pathogens, however, were detected at low numbers: M. haemophilum (arithmetic mean = 1.5% of hsp65 sequences) and M. abscessus (arithmetic mean = 0.006% of hsp65 sequences). Sulfate-reducing bacteria from the genus Desulfovibrio, which have been implicated in microbially-influenced corrosion, dominated all communities located underneath corrosion tubercules (arithmetic mean = 67.5% of the community). This research provides novel insights into the quantity and composition of biofilms in full-scale drinking water distribution systems, which is critical for assessing the risks to public health and to the water supply infrastructure.