Microorganisms from surface waters contribute to the inactivation of human echovirus 11: toward biocontrol of viral pathogens?

Human viruses are widespread as contaminants in surface waters and represent a significant health risk. Viral pathogens can persist in aquatic ecosystems and cause infections via contaminated water or food. Among the different factors governing the environmental persistence of enteric viruses, removal by indigenous microorganisms, in particular predation by protists, has received little attention to date. This study aims to determine the contribution of indigenous protists to the inactivation of human viruses in different surface waters. Incubation of human echovirus 11 (E11) in water from Lake Geneva and seawater led to an inactivation of 2.5-log within 48 hours at 22°C, whereas inactivation in sterile controls was minor (0.8-log reduction). This inactivation was mainly attributed to the action of protists in the eukaryotic fraction of the samples. The inactivation of viruses was shown to be temperature-dependent, with a complete inhibition of biological inactivation at 8°C. In addition, inactivation depended on both the species of virus and protist species. Among three protist isolates tested (Paraphysomonas sp., Uronema marinum and Caecitellus paraparvulus), Caecitellus paraparvuluswas particularly efficient at removing E11 (2.1-log reduction over four days with an initial protists concentration of 1000 cells / ml). In conclusion, this study suggests that indigenous protists present in lakes and oceans are important biological contributors to the inactivation of E11. These results pave the way for further research to better understand how protists control human viral pathogens in aquatic ecosystems and how microbial inactivation could be exploited as a water treatment solution to enhance microbial safety.

Competitive advantage of Rumex obtusifolius L. might increase in intensively managed temperate grasslands under drier climate

Constant Signarbieux

Climate models predict decreasing amounts of precipitation for future summers in Switzerland. Since grasslands cover about one quarter of the area, severe consequences might be expected for Swiss agriculture, ranging from loss of grassland productivity to changes in vegetation composition. Since stressed ecosystems are also more susceptible to invasion, future drier conditions might favour the emergence of weeds. However, the response of temperate grasslands to drought has not been investigated in great detail so far. Using transparent rain shelters, we simulated extreme summer drought conditions in intensively managed temperate grassland in the Swiss lowlands at 400 m (Chamau, located near the city of Lucerne) and studied the drought response of Rumex obtusifolius, one of the most troublesome weeds for forage production. We quantified above-ground biomass and assessed the resource use in terms of carbon, nitrogen and water. R. obtusifolius increased its above-ground biomass production in response to drought, comprising up to 80% of the total community biomass in 2006. Within the drought plots, highest pre-dawn leaf water potentials, high values for midday leaf water potentials, stomatal conductance and assimilation clearly indicated that R. obtusifolius was much less affected by drought than other plant species. In general, no significant differences were found for these variables between drought and control R. obtusifolius plants, in contrast to the other plant species. Higher water use efficiency together with a change in N acquisition patterns resulted in a competitive advantage of R. obtusifolius over other species, favouring the spread of this weed. Thus, our results suggest a potential increase of weed pressure by R. obtusifolius under future climatic conditions, demanding additional management measures to limit its success. © 2009 Elsevier B.V. All rights reserved.

Elsevier2010

Environmental and taxonomic controls of carbon and oxygen stable isotope composition in Sphagnum across broad climatic and geographic ranges

Luca Bragazza, Mariusz Lamentowicz, Bjorn Jozef Maria Robroek

Rain-fed peatlands are dominated by peat mosses (Sphagnum sp.), which for their growth depend on nutrients, water and CO2 uptake from the atmosphere. As the isotopic composition of carbon (C-12(,)13) and oxygen (O-16(,)18) of these Sphagnum mosses are affected by environmental conditions, Sphagnum tissue accumulated in peat constitutes a potential long-term archive that can be used for climate reconstruction. However, there is inadequate understanding of how isotope values are influenced by environmental conditions, which restricts their current use as environmental and palaeoenvironmental indicators. Here we tested (i) to what extent C and O isotopic variation in living tissue of Sphagnum is speciesspecific and associated with local hydrological gradients, climatic gradients (evapotranspiration, temperature, precipitation) and elevation; (ii) whether the C isotopic signature can be a proxy for net primary productivity (NPP) of Sphagnum; and (iii) to what extent Sphagnum tissue delta O-18 tracks the delta O-18 isotope signature of precipitation. In total, we analysed 337 samples from 93 sites across North America and Eurasia us ing two important peat-forming Sphagnum species (S. magellanicum, S. fuscum) common to the Holarctic realm. There were differences in delta C-13 values between species. For S. magellanicum delta C-13 decreased with increasing height above the water table (HWT, R-2 = 17 %) and was positively correlated to productivity (R-2 = 7 %). Together these two variables explained 46 % of the between-site variation in delta C-13 values. For S. fuscum, productivity was the only significant predictor of delta C-13 but had low explanatory power (total R-2 = 6 %). For delta O-18 values, approximately 90 % of the variation was found between sites. Globally modelled annual delta O-18 values in precipitation explained 69 % of the between-site variation in tissue delta O-18. S. magellanicum showed lower delta O-18 enrichment than S. fuscum (-0.83 %0 lower). Elevation and climatic variables were weak predictors of tissue delta O-18 values after controlling for delta O-18 values of the precipitation. To summarize, our study provides evidence for (a) good predictability of tissue delta O-18 values from modelled annual delta O-18 values in precipitation, and (b) the possibility of relating tissue delta C-13 values to HWT and NPP, but this appears to be species-dependent. These results suggest that isotope composition can be used on a large scale for climatic reconstructions but that such models should be species-specific.

COPERNICUS GESELLSCHAFT MBH2018

Control of Waterborne Human Viruses by Indigenous Bacteria and Protists Is Influenced by Temperature, Virus Type, and Microbial Species

Anna Carratala Ripolles, Charles Zeng Gan, Tamar Kohn, Margot Ninon Lauren Olive

Human viruses are ubiquitous contaminants in surface waters, where they can persist over extended periods of time. Among the factors governing their environmental persistence, the control (removal or inactivation) by microorganisms remains poorly understood. Here we determined the contribution of indigenous bacteria and protists to the decay of human viruses in surface waters. Incubation of echovirus 11 (E11) in freshwater from Lake Geneva and seawater from the Mediterranean Sea led to a 2.5-log10 reduction in the infectious virus concentration within 48 hours at 22°C, whereas E11 was stable in sterile controls. The observed virus reduction was attributed to the action of both bacteria and protists in the biologically active matrices. The effect of microorganisms on viruses was temperature-dependent, with a complete inhibition of microbial virus control in lake water at temperatures ≤ 16°C. Among three protist isolates tested (Paraphysomonas sp., Uronema marinum and Caecitellus paraparvulus), Caecitellus paraparvulus was particularly efficient at controlling E11 (2.1-log10 reduction over four days with an initial protists concentration of 103 cells × ml-1). In addition, other viruses (human adenovirus type 2 and bacteriophage H6) exhibited different grazing kinetics compared to E11, indicating that the efficacy of antiviral action also depended on the type of virus. In conclusion, indigenous bacteria and protists in lake water and seawater can modulate the persistence of E11. These results pave the way for further research to understand how microorganisms control human viral pathogens in aquatic ecosystems and to exploit this process as a treatment solution to enhance microbial water safety.