skip to main content


Title: Impact of Metazooplankton Filter Feeding on Escherichia coli under Variable Environmental Conditions
ABSTRACT The fecal indicator bacterial species Escherichia coli is an important measure of water quality and a leading cause of impaired surface waters. We investigated the impact of the filter-feeding metazooplankton Daphnia magna on the inactivation of E. coli . The E. coli clearance rates of these daphnids were calculated from a series of batch experiments conducted under variable environmental conditions. Batch system experiments of 24 to 48 h in duration were completed to test the impacts of bacterial concentration, organism density, temperature, and water type. The maximum clearance rate for adult D. magna organisms was 2 ml h −1 organism −1 . Less than 5% of E. coli removed from water by daphnids was recoverable from excretions. Sorption of E. coli on daphnid carapaces was not observed. As a comparison, the clearance rates of the freshwater rotifer Branchionus calyciflorus were also calculated for select conditions. The maximum clearance rate for B. calyciflorus was 6 × 10 −4  ml h −1 organism −1 . This research furthers our understanding of the impacts of metazooplankton predation on E. coli inactivation and the effects of environmental variables on filter feeding. Based on our results, metazooplankton can play an important role in the reduction of E. coli in natural treatment systems under environmentally relevant conditions. IMPORTANCE Escherichia coli is a fecal indicator bacterial species monitored by the U.S. Environmental Protection Agency to assess microbial water quality. Due to the potential human health implications linked to high levels of E. coli , it is important to understand the inactivation or reduction mechanisms in surface waters. Our research examines the capacities of two types of widespread filter-feeding freshwater metazooplankton, Daphnia magna and Brachionus calyciflorus , to reduce E. coli concentrations. We examine the impacts of different environmentally relevant conditions on the clearance rates. Our results contribute to a better understanding of the importance of metazooplankton in controlling E. coli concentrations and what conditions will reduce or increase grazing. These results provide baseline data to support future efforts to develop a quantitative model relating zooplankton uptake rates to relevant environmental variables.  more » « less
Award ID(s):
1804941
NSF-PAR ID:
10125869
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Applied and Environmental Microbiology
Volume:
85
Issue:
23
ISSN:
0099-2240
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. null (Ed.)
    Treatment wetlands can remove a wide range of pollutants from wastewater and stormwater runoff, including microbial pollutants such as Escherichia coli . Filter feeding zooplankton play an important role in improving water quality in treatment wetlands through grazing and subsequent inactivation of E. coli . Understanding how climate change will impact the various processes governing microbial inactivation in treatment wetlands is essential to ensure adequately treated water. We investigated the impact of interacting environmental factors on the E. coli clearance rate of a keystone zooplankton species, Daphnia magna . We utilized a full factorial experimental design to test the impacts of food abundance, food type, and temperature in flow-through mesocosms under environmentally relevant conditions. Temperature and food abundance interactions were significant, which highlights the importance of studying multiple environmental variables when considering the filter feeding contributions of zooplankton. While both food abundance and temperature had a significant impact on clearance rate, daphnids did not exhibit a preference between algae or E. coli , which were the two food sources used in our studies. We observed that at 25 °C, food abundance and type had a larger impact on E. coli clearance rate than at 15 °C, which has important implications when considering resiliency of treatment wetlands in a warming climate. Our findings show that zooplankton filtration behavior will be impacted by environmental conditions that are projected due to climatic changes, but populations can still inactivate E. coli and improve water quality when exposed to these conditions. 
    more » « less
  2. Fecal contamination is a significant source of water quality impairment globally. Aquatic ecosystems can provide an important ecosystem service of fecal contamination removal. Understanding the processes that regulate the removal of fecal contamination among river networks across flow conditions is critical. We applied a river network model, the Framework for Aquatic Modeling in the Earth System (FrAMES-Ecoli), to quantify removal of fecal indicator bacteria by river networks across flow conditions during summers in a series of New England watersheds of different characteristics. FrAMES-Ecoli simulates sources, transport, and riverine removal of Escherichia coli (E. coli). Aquatic E. coli removal was simulated in both the water column and the hyporheic zone, and is a function of hydraulic conditions, flow exchange rates with the hyporheic zone, and die-off in each compartment. We found that, at the river network scale during summers, removal by river networks can be high (19–99%) with variability controlled by hydrologic conditions, watershed size, and distribution of sources in the watershed. Hydrology controls much of the variability, with 68–99% of network scale inputs removed under base flow conditions and 19–85% removed during storm events. Removal by the water column alone could not explain the observed pattern in E. coli, suggesting that processes such as hyporheic removal must be considered. These results suggest that river network removal of fecal indicator bacteria should be taken into consideration in managing fecal contamination at critical downstream receiving waters. 
    more » « less
  3. Gralnick, Jeffrey A. (Ed.)
    ABSTRACT The use of enterococci as a fecal indicator bacterial group for public health risk assessment has been brought into question by recent studies showing that “naturalized” populations of Enterococcus faecalis exist in the extraenteric environment. The extent to which these naturalized E. faecalis organisms can confound water quality monitoring is unclear. To determine if strains isolated from different habitats display different survival strategies and responses, we compared the decay patterns of three E. faecalis isolates from the natural environment (environmental strains) against three human gut isolates (enteric strains) in laboratory mesocosms that simulate an oligotrophic, aerobic freshwater environment. Our results showed similar overall decay rates between enteric and environmental isolates based on viable plate and quantitative PCR (qPCR) counts. However, the enteric isolates exhibited a spike in copy number ratios of 16S rRNA gene transcripts to 16S rRNA gene DNA copies (rRNA:rDNA ratios) between days 1 and 3 of the mesocosm incubations that was not observed in environmental isolates, which could indicate a different stress response. Nevertheless, there was no strong evidence of differential gene expression between environmental and enteric isolates related to habitat adaptation in the accompanying mesocosm metatranscriptomes. Overall, our results provide novel information on how rRNA levels may vary over different growth conditions (e.g., standard lab versus oligotrophic) for this important indicator bacteria. We also observed some evidence for habitat adaptation in E. faecalis ; however, this adaptation may not be substantial or consistent enough for integration in water quality monitoring. IMPORTANCE Enterococci are commonly used worldwide to monitor environmental fecal contamination and public health risk for waterborne diseases. However, closely related enterococci strains adapted to living in the extraenteric environment may represent a lower public health risk and confound water quality estimates. We developed an rRNA:rDNA viability assay for E. faecalis (a predominant species within this fecal group) and tested it against both enteric and environmental isolates in freshwater mesocosms to assess whether this approach can serve as a more sensitive water quality monitoring tool. We were unable to reliably distinguish the different isolate types using this assay under the conditions tested; thus, environmental strains should continue to be counted during routine water monitoring. However, this assay could be useful for distinguishing more recent (i.e., higher-risk) fecal pollution because rRNA levels significantly decreased after 1 week in all isolates. 
    more » « less
  4. Abstract

    Advanced treated municipal wastewater is an important alternative water source for agricultural irrigation. However, the possible persistence of chemical and microbiological contaminants in these waters raise potential safety concerns with regard to reusing treated wastewater for food crop irrigation. Two low-cost and environmentally-friendly filter media, biochar (BC) and zero-valent iron (ZVI), have attracted great interest in terms of treating reused water. Here, we evaluated the efficacy of BC-, nanosilver-amended biochar- (Ag-BC) and ZVI-sand filters, in reducing contaminants of emerging concern (CECs),Escherichia coli (E. coli)and total bacterial diversity from wastewater effluent. Six experiments were conducted with control quartz sand and sand columns containing BC, Ag-BC, ZVI, BC with ZVI, or Ag-BC with ZVI. After filtration, Ag-BC, ZVI, BC with ZVI and Ag-BC with ZVI demonstrated more than 90% (> 1 log) removal ofE. colifrom wastewater samples, while BC, Ag-BC, BC with ZVI and Ag-BC with ZVI also demonstrated efficient removal of tested CECs. Lower bacterial diversity was also observed after filtration; however, differences were marginally significant. In addition, significantly (p < 0.05) higher bacterial diversity was observed in wastewater samples collected during warmer versus colder months. Leaching of silver ions occurred from Ag-BC columns; however, this was prevented through the addition of ZVI. In conclusion, our data suggest that the BC with ZVI and Ag-BC with ZVI sand filters, which demonstrated more than 99% removal of both CECs andE. coliwithout silver ion release, may be effective, low-cost options for decentralized treatment of reused wastewater.

    Graphical Abstract

     
    more » « less
  5. We introduce the facile one-step biosynthesis of a bilayer structured hydrogel composite of reduced-graphene oxide (rGO) and bacterial nanocellulose (BNC) for multiple photothermal water treatment applications. One-step in situ biosynthesis of a bilayered hydrogel was achieved via modification of BNC growth medium supplemented with an optimized concentration of corn steep liquor as a growth enhancer. A two-stage, growth rate-controlled formation mechanism for the bilayer structure was revealed. The final cleaned and freeze-dried reduced-GO embedded BNC bilayer membrane enables versatile applications such as filtration (tested using gold nanoparticles, Escherichia coli cells, and plasmid DNA), photothermal disinfection of entrapped E. coli , and solar water evaporation. Comparable particle rejection (up to ≈4 nm) and water flux (146 L h −1 m −2 ) to ultrafiltration were observed. Entrapment and photothermal inactivation of E. coli cells were accomplished within 10 min of solar exposure (one sun). Such treatment can potentially suppress membrane biofouling. The steam generation capacity was 1.96 kg m −2 h −1 . Our simple and scalable approach opens a new path for biosynthesis of nanostructured materials for environmental and biomedical applications. 
    more » « less