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

SHOME NANDINI; RAJAL, VERONICA; SWARUP SANJAY; MARZINELLI EZEQUIEL; NG ALBERT; CRUZ, MERCEDES CECILIA; TAY MARTIN; YUNG MARIA; SANTILLAN EZEQUIEL; MOSES DANIELA; ARUMUGAN, KRITHIKA; WILLIAMS, ROHAN; WUERTZ, STEFAN

Conferencia; UNC Water Microbiology Conference 2017; 2017

ACEPTADO PARA POSTERWe studied the fate and transport of common waterborne pathogens in freshwatersystems using simple hydrodynamic modeling and their effect on mature biofilmcommunities using metagenomic sequencing. The four surrogates representing pathogenswere Pseudomonas aeruginosa, Enterococcus faecalis and the bacteriophages P22 and GA.We ran a set of four experiments, at two different flow rates, 6 L min-1 (low) and 12 L min-1(high). The flow rates represented conditions in urban canals during dry weather and theannual average. In each experiment, we operated four open channel flumes with partialrecirculation (laminar flow range), and two of the flumes were spiked with the surrogates.Spiking was done once and concentrations of viable populations and their nucleic acids inwater and biofilm were followed for 21 days. The remaining flumes received no surrogates.Additionally, microbial community assembly was monitored through metagenomicsequencing of the biofilms collected from flumes with and without surrogates.At low flow settling and decay terms alone could not explain bulk waterconcentrations in the presence of biofilms. Surrogates attached to biofilms within 24 hoursand P. aeruginosa and E. faecalis were also found to grow within biofilms. BacteriophageP22 was unable to multiply due to the absence of its host, but was retained in the biofilmthroughout the experimental period. Bacteriophage GA was not detected in the flumes afterspiking. Surrogates were also released into the overlying water column, thereby increasingthe number of days required for complete removal of the organisms from the flumes. At lowflow, P. aeruginosa was initially released continuously from the biofilm. Later, detachmentwas more random and occurred to a greater extent than expected based on erosion alone,suggesting sloughing via biological dispersal. P22 detachment was by erosion and E. faecalisdid not detach.In comparison, at the high flow rate, the role of biofilms as a source and sink ofsurrogates remained the same. However, release of P. aeruginosa was through continuouserosion, as compared to random sloughing at the low flow rate. The two-log reduction timesof surrogates in water were 24-57% higher and those in biofilms were 35-500% lower at highflow than at low flow. Concurrently, the detachment rates in biofilms were almost 80% higherand decay in biofilms was 22- 83% faster at high flow rate. Growth of P. aeruginosa waseither absent or balanced by increased decay at high flow, whereas the growth rate of E.faecalis doubled at high flow. Community analysis revealed that the prokaryotic communitieswere not affected by surrogate addition at any flow rate. Eukaryotic communities showedsimilar trends. However, in two experiments, when Podocopida and Haplotaxida werepresent, the abundance of these organisms was related to the presence of surrogates, eventhough the latter were not pathogenic for any of them. Overall, nascent eukaryoticcommunities changed due to algal growth, while prokaryotic communities remained thesame. In conclusion, freshwater microbial communities were resilient to pathogen exposureand surrogates survived in biofilms through co-existence and not invasion.