How does the cladoceran Daphnia pulex affect the fate of Escherichia coli in water?
The faecal indicator Escherichia coli plays a central role in water quality assessment and monitoring. It is therefore essential to understand its fate under various environmental constraints such as predation by bacterivorous zooplankton. Whereas most studies have examined how protozooplankton communities (heterotrophic nanoflagellates and ciliates) affect the fate of E. coli in water, the capacity of metazooplankton to control the faecal indicator remains poorly understood. In this study, we investigated how the common filter-feeding cladoceran, Daphnia pulex, affects the fate of E. coli under different experimental conditions. Daphnia ingested E. coli and increased its loss rates in water, but the latter rates decreased from 1.65 d-1 to 0.62 d-1 after a 1,000-fold reduction in E. coli initial concentrations, due to lower probability of encounter between Daphnia and E. coli. The combined use of culture and PMA qPCR (viability-qPCR) demonstrated that exposure to Daphnia did not result into the formation of viable but non-culturable E. coli cells. In lake water, a significant part of E. coli population loss was associated with matrix-related factors, most likely due to predation by other bacterivorous biota and/or bacterial competition. However, when exposing E. coli to a D. pulex gradient (from 0 to 65 ind.L-1), we observed an increasing impact of Daphnia on E. coli loss rates, which reached 0.47 d-1 in presence of 65 ind.L-1. Our results suggest that the filter-feeder can exert a non-negligible predation pressure on E. coli, especially during seasonal Daphnia population peaks. Similar trials using other Daphnia species as well as stressed E. coli cells will increase our knowledge on the capacity of this widespread zooplankter to control E. coli in freshwater resources. Based on our results, we strongly advocate the use of natural matrices to study these biotic interactions in order to avoid overestimation of Daphnia impact.
Canada Research Chair in Source Water Protection, Department of Civil, Geological and Mining Engineering, Polytechnique Montreal, Montreal, Quebec, Canada.
Jean-Baptiste
JB
Burnet
Canada Research Chair in Source Water Protection, Department of Civil, Geological and Mining Engineering, Polytechnique Montreal, Montreal, Quebec, Canada.
Tarek
T
Faraj
Environmental Research and Innovation, Luxembourg Institute of Science and Technology, Esch-sur-Alzette, Luxembourg.
Henry-Michel
HM
Cauchie
Laboratoire d'Écologie Animale et d'Écotoxicologie, Institut de Chimie, Université de Liège, Liège, Belgium.
Célia
C
Joaquim-Justo
Écologie des Systèmes Aquatiques, Université Libre de Bruxelles, Campus de la Plaine, CP 221, Boulevard du Triomphe, Bruxelles, Belgium.
Pierre
P
Servais
NSERC Industrial Chair on Drinking Water, Department of Civil, Geological and Mining Engineering, Polytechnique Montreal, Montreal, Quebec, Canada.
Michèle
M
Prévost
Canada Research Chair in Source Water Protection, Department of Civil, Geological and Mining Engineering, Polytechnique Montreal, Montreal, Quebec, Canada.
Sarah M
SM
Dorner
D000821:Animal Feed; D000818:Animals; D003621:Daphnia; D004784:Environmental Monitoring; D004926:Escherichia coli; D060106:Lakes; D050296:Microbial Viability; D014867:Water; D014871:Water Microbiology
D014867:Water