Influence of Microplastics on Microbial Structure, Function, and Mechanical Properties of Stream Periphyton

Este artículo contiene 17 páginas, 5 figuras, 4 tablas.Periphyton is a freshwater biofilm composed of prokaryotic and eukaryotic communities that occupy rocks and sediments, forming the base of the food web and playing a key role in nutrient cycling. Given the large surface that periphyton comprises, it may also act as a sink for a diverse range of man-made pollutants, including microplastics (MP). Here we investigated the effect of 1–4 μm and 63–75 µm sized, spherical polyethylene MP with native and ultraviolet (UV)-weathered surface on developing natural stream periphyton communities over 28 days. In order to ensure proper particle exposure, we first tested MP suspension in water or in water containing either Tween 80, extracellular polymeric substances – EPS, fulvic acids, or protein. We found the extract of EPS from natural periphyton to be most suitable to create MP suspensions in preparation of exposure. Upon exposure, all tested types of MP were found to be associated with the periphyton, independent of their size and other properties. While biomass accrual and phenotypic community structure of the photoautotrophs remained unchanged, the prokaryotic and eukaryotic communities experienced a significant change in composition and relative abundances. Moreover, alpha diversity was affected in eukaryotes, but not in prokaryotes. The observed changes were more prominent in periphyton exposed to UV-treated as compared with native surface MP. Mechanical properties, as assessed by compression rheology, showed that MP-exposed periphyton had longer filamentous streamers, higher stiffness, lower force recovery and a higher viscoelasticity than control periphyton. Despite the observed structural and mechanical changes of periphyton, functional parameters (i.e., photosynthetic yield, respiration and nutrient uptake efficiencies) were not altered by MP, indicating the absence of MP toxicity, and suggesting functional redundancy in the communities. Together, our results provide further proof that periphyton is a sink for MP and demonstrate that MP can impact local microbial community composition and mechanical properties of the biofilms. Consequences of these findings might be a change in dislodgement behavior of periphyton, a propagation through the food chains and impacts on nutrient cycling and energy transfer. Hence, taking the omnipresence, high persistence and material and size diversity of MP in the aquatic environment into account, their ecological consequences need further investigation.The study was financially supported by the Velux foundation, project number 1039, Switzerland. Additional lab work was funded by Tailwind grant of Eawag Switzerland. Open access funding was provided by Eawag–Swiss Federal Institute of Aquatic Science And Technology.Peer reviewe

Differential photoinhibition of bacterial and archaeal ammonia oxidation

6 páginas, 1 tablas, 2 figuras.Inhibition by light potentially influences the distribution of ammonia oxidizers in aquatic environments and is one explanation for nitrite maxima near the base of the euphotic zone of oceanic waters. Previous studies of photoinhibition have been restricted to bacterial ammonia oxidizers, rather than archaeal ammonia oxidizers, which dominate in marine environments. To compare the photoinhibition of bacterial and archaeal ammonia oxidizers, specific growth rates of two ammonia-oxidizing archaea (Nitrosopumilus maritimus and Nitrosotalea devanaterra) and bacteria (Nitrosomonas europaea and Nitrosospira multiformis) were determined at different light intensities under continuous illumination and light/dark cycles. All strains were inhibited by continuous illumination at the highest intensity (500 μE m−2 s−1). At lower light intensities, archaeal growth was much more photosensitive than bacterial growth, with greater inhibition at 60 μE m−2 s−1 than at 15 μE m−2 s−1, where bacteria were unaffected. Archaeal ammonia oxidizers were also more sensitive to cycles of 8-h light/16-h darkness at two light intensities (60 and 15 μE m−2 s−1) and, unlike bacterial strains, showed no evidence of recovery during dark phases. The findings provide evidence for niche differentiation in aquatic environments and reduce support for photoinhibition as an explanation of nitrite maxima in the ocean.The project was financed by the GRACCIE project (Spanish Ministry of Science and Education Consolider Program, ref: CSD2007-00067). S.N.M. is supported by a JAE-pre-doctoral fellowship from the Spanish National Research Council (CSIC), and G.W.N. by a NERC Advanced Fellowship (NE/D010195/1). Additional support was from NSF Award MCB-0920741 to D.A.S. and M. Hackett and from NSF Award OCE-1046017 to D.A.S., A. Ingalls, E.V. Armbrust, A.H. Devol and J. Moffett.Peer reviewe

Colonization of freshwater biofilms by nitrifying bacteria from activated sludge

12 páginas, 5 figuras, 2 tablas.Effluents from wastewater treatment plants (WWTPs) containing microorganisms and residual nitrogen can stimulate nitrification in freshwater streams. We hypothesized that different ammonia-oxidizing (AOB) and nitriteoxidizing (NOB) bacteria present in WWTP effluents differ in their potential to colonize biofilms in the receiving streams. In an experimental approach, we monitored biofilm colonization by nitrifiers in ammonium- or nitrite-fed microcosm flumes after inoculation with activated sludge. In a field study, we compared the nitrifier communities in a full-scale WWTP and in epilithic biofilms downstream of the WWTP outlet. Despite substantially different ammonia concentrations in the microcosms and the stream, the same nitrifiers were detected by fluorescence in situ hybridization in all biofilms. Of the diverse nitrifiers present in the WWTPs, only AOB of the Nitrosomonas oligotropha/ureae lineage and NOB of Nitrospira sublineage I colonized the natural biofilms. Analysis of the amoA gene encoding the alpha subunit of ammonia monooxygenase of AOB revealed seven identical amoA sequence types. Six of these affiliated with the N. oligotropha/ureae lineage and were shared between the WWTP and the stream biofilms, but the other shared sequence type grouped with the N. europaea/eutropha and N. communis lineage. Measured nitrification activities were high in the microcosms and the stream. Our results show that nitrifiers from WWTPs can colonize freshwater biofilms and confirm that WWTPaffected streams are hot spots of nitrification.This work was supported by the Austrian Science Fund (FWF) Grant I44-B06, the Max Planck Society and the European Science Foundation Contract ERAS-CT-2003-980409 of the European Commission, DG Research, FP6.Peer reviewe

Vertical segregation and phylogenetic characterization of ammonia-oxidizing Archaea in a deep oligotrophic lake

12 páginas, 6 figuras, 1 tabla.Freshwater habitats have been identified as one of the largest reservoirs of archaeal genetic diversity, with specific lineages of ammonia-oxidizing archaea (AOA) populations different from soils and seas. The ecology and biology of lacustrine AOA is, however, poorly known. In the present study, vertical changes in archaeal abundance by CARD-FISH, quantitative PCR (qPCR) analyses and identity by clone libraries were correlated with environmental parameters in the deep glacial high-altitude Lake Redon. The lake is located in the central Spanish Pyrenees where atmospheric depositions are the main source of reactive nitrogen. Strong correlations were found between abundance of thaumarchaeotal 16S rRNA gene, archaeal amoA gene and nitrite concentrations, indicating an ammonium oxidation potential by these microorganisms. The bacterial amoA gene was not detected. Three depths with potential ammonia-oxidation activity were unveiled along the vertical gradient, (i) on the top of the lake in winter–spring (that is, the 0 oC slush layers above the ice-covered sheet), (ii) at the thermocline and (iii) the bottom waters in summer—autumn. Overall, up to 90% of the 16S rRNA gene sequences matched Thaumarchaeota, mostly from both the Marine Group (MG) 1.1a (Nitrosoarchaeum-like) and the sister clade SAGMGC−1 (Nitrosotalea-like). Clone-libraries analysis showed the two clades changed their relative abundances with water depth being higher in surface and lower in depth for SAGMGC−1 than for MG 1.1a, reflecting a vertical phylogenetic segregation. Overall, the relative abundance and recurrent appearance of SAGMGC−1 suggests a significant environmental role of this clade in alpine lakes. These results expand the set of ecological and thermal conditions where Thaumarchaeota are distributed, unveiling vertical positioning in the water column as a key factor to understand the ecology of different thaumarchaeotal clades in lacustrine environments.This research was supported by grants CRENYC CGL2006-12058 and PIRENA CGL2009-13318 to EOC, and CONSOLIDER grant GRACCIE CSD2007-00067 from the Spanish Office of Science and Innovation (MICINN). JCA benefits from a Juan de la Cierva postdoctoral fellow (MICINN).Peer reviewe

Differences in ammonium oxidizer abundance and N uptake capacity between epilithic and epipsammic biofilms in an urban stream

Este artículo contiene 10 páginas, 3 figuras, 3 tablas.The capacity of stream biofilms to transform and assimilate N in highly N-loaded streams is essential to guarantee the water quality of freshwater resources in urbanized areas. However, the degree of N saturation experienced by urban streams and their response to acute increases in N concentration are largely unknown. We measured changes in the rates of NH4 1 uptake (UNH4) and oxidation (UAO) resulting from experimental increases in NH4 1-N concentration in mature biofilms growing downstream of a wastewater treatment plant (WWTP) and, thus, naturally exposed to high N concentration. We investigated the responses of UNH4 and UAO to NH4 1-N increases and the abundance of NH4 1 oxidizing bacteria and archaea (AOB and AOA) in epilithic and epipsammic biofilms. UNH4 and UAO increased with increasing NH4 1-N concentration for the 2 biofilm types, suggesting no N saturation under ambient levels of NH4 1-N. Thus, these biofilms can contribute to mitigating N excesses and the variability of NH4 1-N concentrations from WWTP effluent inputs. The 2 biofilm types exhibited different Michaelis–Menten kinetics, indicating different capacity to respond to acute increases in NH4 1-N concentration. Mean UNH4 and UAO were 5 higher in epilithic than epipsammic biofilms, coinciding with a higher abundance of AOA1AOB in the former than in the later (76 104 vs 14 104 copies/cm2). AOB derived from active sludge dominated in epilithic biofilms, so our results suggest that WWTP effluents can strongly influence in-stream NH4 1 processing rates by increasing N inputs and by supplying AOA1AOB that are able to colonize some stream habitats.This research was funded by the projects MEDSOUL (CGL2014-59977-C3-2-R), NITRISED (201530E062), and NICUS (CGL-2014-55234-JIN) from the I1D program of the SpanishMinistry of Economy, and funds provided by the European Union Commission. SNM was supported by a JAE predoctoral fellowship from the Spanish National Research Council (CSIC) and fund provided by the Velux Stiftung Swiss Foundation.Peer reviewe

Photoinhibition on natural ammonia oxidizers biofilm populations and implications for nitrogen uptake in stream biofilms

12 páginas, 4 tablas, 4 figuras.We investigated photoinhibition on natural communities of ammonia oxidizing (AO) archaea (AOA) and bacteria (AOB) embedded in complex stream biofilms, and its implications on nitrogen uptake at biofilm scale. Based on the strong photoinhibition previously exhibited by free living and cultured AOA and AOB, we expected AO activity to decrease in biofilms experimentally exposed to light, reducing the contribution of microbial nitrification to ammonium uptake. To test it, we conducted light manipulation experiments in mesocosms using biofilms naturally developed on stream cobbles sides both exposed to light (light-side) and facing the sediment (dark-side). We observed a strong AO photoinhibition in dark-side biofilms, accompanied by either biofilm-scale decreases in nitrification or increases in nitrogen uptake likely by heterotrophic activity. Conversely, in light-side biofilms photoinhibition was not observed suggesting that photoautotrophic layers may protect AO in situ by a sunshade effect. Experimental light and dark alternation cycles stimulated AO, enhancing both nitrification and ammonium uptake. These results support photoinhibition effects on natural AO communities, especially in biofilms developed under ambient dark conditions, whereas this effect seems to be buffered in biofilms developed under light conditions. Therefore, the contribution of nitrification to ammonium uptake at biofilm scale should consider not only the physiological study of AOA and AOB, but also the environmental conditions and community structure at the habitat microscale, since they may counterbalance, among others, the damaging light effects under natural conditions.S.N.M. was supported by a JAE predoctoral fellowship from the Spanish National Research Council (CSIC) and S.B. by funding provided by the Spanish Research Council (JAE-DOC027) and the NICUS project (CGL2014-55234-JIN) from the Spanish Office for Research (MINECO). This research was granted by DARKNESS CGL2012-32747 to EOC and MED_FORESTREAM CGL2011-30590-CO2-02 (MINECO) and REFRESH- 244121 (7th Framework Programme EU Commission) to EM.Peer reviewe

Biofilm recovery in a wastewater treatment plant-influenced stream and spatial segregation of ammonia-oxidizing microbial populations

We monitored the effects of wastewater treatment plant (WWTP) inputs on the recovery of stream biofilms after a large flood event that eroded most of the former biofilm communities. We monitored biomass recovery, chlorophyll a, nitrogen content, and stable isotope natural abundance (15N) over 8 weeks in light- and dark-exposed biofilms upstream and downstream from WWTP inputs, respectively, as well as the abundance of ammonia oxidizers by quantitative polymerase chain reaction. Biomass and chlorophyll a recovered quickly (< 2 weeks), and were significantly higher for light- than for dark-exposed biofilms. There was no consistent effect of WWTP inputs on these parameters, except for the biomass on dark-exposed biofilm that was higher at the WWTP-influenced sites. The influence of the WWTP inputs on stream-water ammonium concentration and its isotopic 15N signature increased as the flood receded. Biofilm 15N downstream of WWTP increased over time, tracking the increase in 15N-ammonium from the WWTP waters. Bacterial and archaeal ammonia oxidizers were present within the biofilm assemblages from early stages of postflood recovery. However, spatial distribution of these two clades was clearly segregated among sites and between light- and dark-exposed biofilms, probably related to ammonium availability and the development of photoautotrophic organisms.Peer reviewe