Link between flow regime, biofilm properties and pathogen fate in freshwater mesocosm flumes in an urban tropical setting

STEFAN WUERTZ; D. MOSES; CRUZ, MERCEDES CECILIA; SWARUP, SANJAY; K. ARUMUGAM; TAY, MARTIN; MARZINELLI, EZEQUIEL; NANDINI SHOME; R.B.H. WILLIAMS; Y. P. YUNG; A. NG; RAJAL, VERONICA BEATRIZ

Chapel Hill

Simposio; 19th International Symposium on Health-Related Water Microbiology; 2017

We studied the fate and transport of common waterborne pathogen surrogates in freshwater systems using simple hydrodynamic modeling and their effect on mature biofilm communities using metagenomic sequencing. The surrogates were Pseudomonas aeruginosa, Enterococcus faecalis and the bacteriophages P22 and GA. The flow rates represented conditions in urban canals during dry weather and the annual average. In each experiment, we operated four open channel flumes with partial recirculation, and two of the flumes were spiked with the surrogates. Spiking was done once and concentrations of viable populations and their nucleic acids were followed for 21 days. Surrogates attached to biofilms within 24 hours and P. aeruginosa and E. faecalis were found to grow within biofilms. Bacteriophage P22 was unable to multiply due to the absence of its host, but was retained in the biofilm throughout the experimental period. Surrogates were also released into the overlying water column, thereby increasing the number of days required for complete removal of the organisms from the flumes. At low flow, P. aeruginosa was initially released continuously from the biofilm. Later, detachment was more random, suggesting sloughing via biological dispersal. P22 detachment was by erosion and E. faecalis did not detach. At the high flow rate, release of P. aeruginosa was through continuous erosion. The two-log reduction times of surrogates in water were 24-57% higher and those in biofilms were 0.35-5 times lower at high flow than at low flow. Concurrently, the detachment rates in biofilms were almost 80% higher and decay in biofilms was 22-83% faster at high flow rate. Community analysis revealed that the prokaryotic communities were not affected by surrogate addition at any flow rate. Eukaryotic communities showed similar trends. In conclusion, freshwater microbial communities were resilient to pathogen exposure and surrogates survived in biofilms through co-existence and not invasion.