Dissipation of pesticides by stream biofilms is influenced by hydrological histories.

To evaluate the effects of hydrological variability on pesticide dissipation capacity by stream biofilms, we conducted a microcosm study. We exposed biofilms to short and frequent droughts (daily frequency), long and less frequent droughts (weekly frequency) and permanently immersed controls, prior to test their capacities to dissipate a cocktail of pesticides composed of tebuconazole, terbuthylazine, imidacloprid, glyphosate and its metabolite aminomethylphosphonic acid. A range of structural and functional descriptors of biofilms (algal and bacterial biomass, extracellular polymeric matrix (EPS) concentration, microbial respiration, phosphorus uptake and community-level physiological profiles) were measured to assess drought effects. In addition, various parameters were measured to characterise the dynamics of pesticide dissipation by biofilms in the different hydrological treatments (% dissipation, peak asymmetry, bioconcentration factor, among others). Results showed higher pesticide dissipation rates in biofilms exposed to short and frequent droughts, despite of their lower biomass and EPS concentration, compared to biofilms in immersed controls or exposed to long and less frequent droughts. High accumulation of hydrophobic pesticides (tebuconazole and terbuthylazine) was measured in biofilms despite the short exposure time (few minutes) in our open-flow microcosm approach. This research demonstrated the stream biofilms capacity to adsorb hydrophobic pesticides even in stressed drought environments.

Comparison of microbial colonization between natural and plastic substrata in a polluted watershed.

Plastic pollution represents a threat for biological communities and the ecological functions they provide in river ecosystems. In this study, we compared the microbial colonization of two plastics (biodegradable and non-biodegradable) and three natural substrata (leaves, sediment, and rocks) in two study sites of an urbanized watershed differing in their plastic-contamination degree (upstream and downstream). The density and diversity of bacterial, fungal, and algal communities, as well as the extracellular enzymatic activities ß-glucosidase (GLU), N-acetyl-glucosaminidase (NAG), and phosphatase (PHO), were analysed in each substrata and site over a 4-week colonization experiment. Results showed higher microbial densities and enzymatic activities in leaves and sediment compared to plastics and rocks, probably due to the greater availability of organic carbon and nutrients in the former substrata. However, the microbial colonization of the two plastics was only different in the downstream site, where bacterial density and enzymatic activities were higher in the biodegradable plastic compared to the non-biodegradable plastic. Accordingly, the presence of biodegradable plastics would enhance the heterotrophic metabolism in plastic-polluted rivers.

Litter decomposition of three halophytes in a Mediterranean salt marsh: Relevance of litter quality, microbial activity and microhabitat.

Studies of litter decomposition in salt marshes have been mainly focused on the measurement of decomposition rates, being litter quality, the type of microbial decomposers and their extracellular enzyme activity, rarely considered. Moreover, most of these studies have been conducted in Poaceae and Cyperaceae species, being scarce the literature on Chenopodiaceae species, which are abundant in Mediterranean salt marshes. Here we analyse the litter decomposition process of two Chenopodiaceae (Sarcocornia fruticosa and Halimione portulacoides) and one Poaceae (Elytrigia atherica) species, belonging S. fruticosa to a halophilous scrub habitat and the other two to a salt meadow habitat of a Mediterranean salt marsh. For each species, we analysed litter decomposition rates, litter quality, fungal and bacterial biomass and potential extracellular enzymes activities. In order to embrace the spatial heterogeneity, two zones were considered within each habitat. Litter of E. atherica decomposed 7- and 13-fold slower than those of S. fruticosa and H. portulacoides, respectively, suggesting that this species is the one that would favour most the carbon sequestration into the soil. The different decomposition rates would be explained by the higher initial lignin and cellulose content of E. atherica rather than by the initial carbon and nitrogen content and C/N ratio. Moreover, enzyme efficiency, compared to enzyme activity, better contributes to explain the different decomposition rates observed. Bacteria dominated throughout the litter decomposition process regardless the species, but fungi increased their relevance in the later stages, when the relative lignin litter content increased. Litter decomposition was affected by microhabitat spatial differences, although the responses depended on the species. Hence, flooding (in the habitat of S. fruticosa) or soil texture (in the habitat of E. atherica and H. portulacoides) might have modulated the decomposition process, being H. portulacoides the most sensitive species to the spatial differences of the salt meadow habitat.

River biofilms adapted to anthropogenic disturbances are more resistant to WWTP inputs.

The sensitivity and spatial recovery of river sediment biofilms along 1 km after the input of two wastewater treatment plants (WWTPs) located in two river reaches with different degrees of anthropogenic influence were investigated. First, at the upper reach, we observed an inhibition of some microbial functions (microbial respiration and extracellular enzyme activities) and strong shifts in bacterial community composition (16S rRNA gene), whereas an increase in microbial biomass and activity and less pronounced effect on microbial diversity and community composition were seen at the lower reach. Second, at the lower reach we observed a quick spatial recovery (around 200 m downstream of the effluent) as most of the functions and community composition were similar to those from reference sites. On the other hand, bacterial community composition and water quality at the upper reach was still altered 1 km from the WWTP effluent. Our results indicate that biofilms in the upstream sites were more sensitive to the effect of WWTPs due to a lower degree of tolerance after a disturbance than communities located in more anthropogenically impacted sites.

The synergistic effect of enzymatic detergents on biofilm cleaning from different surfaces.

Biofilm growth is a significant source of contamination in the food industry. Enzymes are considered green countermeasures against biofilm formation in the food industry owing to their biodegradability and low toxicity. In this study, the synergistic effect of enzymes was studied against biofilm cleaning from hard surfaces. A mixed-microbial sample was sourced from a meat packaging line and biofilms were grown under high shear conditions on stainless steel and polyethylene surfaces. A model cleaning-in-place (CIP) parallel-plate flow chamber was used for firstly, the enzymatic cleaning and secondly, a disinfection step. The cleaning effectiveness was evaluated in response to different formulations containing non-foaming commercial surfactants among with amylase, protease and lipase at neutral pH. The formulation combining all three enzymes was the most effective, showing a synergy essential for the deformation of biofilm structure and consequently better disinfection of both material surfaces.

Microbial Organic Matter Utilization in High-Arctic Streams: Key Enzymatic Controls.

In the Arctic, climate changes contribute to enhanced mobilization of organic matter in streams. Microbial extracellular enzymes are important mediators of stream organic matter processing, but limited information is available on enzyme processes in this remote area. Here, we studied the variability of microbial extracellular enzyme activity in high-Arctic fluvial biofilms. We evaluated 12 stream reaches in Northeast Greenland draining areas exhibiting different geomorphological features with contrasting contents of soil organic matter to cover a wide range of environmental conditions. We determined stream nitrogen, phosphorus, and dissolved organic carbon concentrations, quantified algal biomass and bacterial density, and characterized the extracellular enzyme activities involved in catalyzing the cleavage of a range of organic matter compounds (e.g., ß-glucosidase, phosphatase, ß-xylosidase, cellobiohydrolase, and phenol oxidase). We found significant differences in microbial organic matter utilization among the study streams draining contrasting geomorphological features, indicating a strong coupling between terrestrial and stream ecosystems. Phosphatase and phenol oxidase activities were higher in solifluction areas than in alluvial areas. Besides dissolved organic carbon, nitrogen availability was the main driver controlling enzyme activities in the high-Arctic, which suggests enhanced organic matter mineralization at increased nutrient availability. Overall, our study provides novel information on the controls of organic matter usage by high-Arctic stream biofilms, which is of high relevance due to the predicted increase of nutrient availability in high-Arctic streams in global climate change scenarios.

OTSC® Proctology vs. fistulectomy and primary sphincter reconstruction as a treatment for low trans-sphincteric anal fistula in a randomized controlled pilot trial.

BACKGROUND: The aim of this study was to compare OTSC® proctology and fistulectomy with primary sphincter reconstruction results as treatment strategies for anorectal low trans-sphincteric fistula. METHODS: Between February 2012 and March 2013, patients affected by trans-sphincteric anal fistula were consecutively enrolled in the trial. Patients were randomized to receive fistulectomy with primary sphincter reconstruction or OTSC® Proctology. Demographic characteristics, comorbodities, previous anorectal treatments, and recurrent fistula data were acquired. Postoperative therapy data and pain and Wexner scores (30 and 60 dd) were acquired during follow-up. Furthermore, patients were contacted by telephone after six months, and were visited both one year and three years after surgery. RESULTS: Thirty consecutive patients were included in the study. 15 patients underwent the OTSC® Proctology procedure and 15 underwent the standard fistulectomy. The success rate was 93.3% in the OTSC group. The mean postoperative stay was 1.3 days in the OTSC® patients and 3.6 days in the fistulectomy group patients. The mean medications required for complete healing was 3.2 in the OTSC group and 8.9 in the FIPS group. CONCLUSIONS: Our results suggest that OTSC® Proctology is an effective and safe treatment in achieving permanent closure of the internal fistula opening in selected patients, with excellent results in terms of pain, postoperative incontinence, healing time, and days of hospitalization.

Deconvolution model to resolve cytometric microbial community patterns in flowing waters.

Flow cytometry is suitable to discriminate and quantify aquatic microbial cells within a spectrum of fluorescence and light scatter signals. Using fixed gating and operational settings, we developed a finite distribution mixture model, followed by the Voronoi tessellation, to resolve bivariate cytometric profiles into cohesive subgroups of events. This procedure was applied to outline recurrent patterns and quantitative changes of the aquatic microbial community along a river hydrologic continuum. We found five major subgroups within each of the commonly retrieved populations of cells with Low and High content of Nucleic Acids (namely, LNA, and HNA cells). Moreover, the advanced analysis allowed assessing changes of community patterns perturbed by a wastewater feed. Our approach for cytometric data deconvolution confirmed that flow cytometry could represent a prime candidate technology for assessing microbial community patterns in flowing waters. © 2017 International Society for Advancement of Cytometry.

Microbial decomposition is highly sensitive to leaf litter emersion in a permanent temperate stream.

Drought frequency and intensity in some temperate regions are forecasted to increase under the ongoing global change, which might expose permanent streams to intermittence and have severe repercussions on stream communities and ecosystem processes. In this study, we investigated the effect of drought duration on microbial decomposition of Populus nigra leaf litter in a temperate permanent stream (Oliveira, NW Portugal). Specifically, we measured the response of the structural (assemblage composition, bacterial and fungal biomass) and functional (leaf litter decomposition, extracellular enzyme activities (EEA), and fungal sporulation) parameters of fungal and bacterial communities on leaf litter exposed to emersion during different time periods (7, 14 and 21d). Emersion time affected microbial assemblages and litter decomposition, but the response differed among variables. Leaf decomposition rates and the activity of ß-glucosidase, cellobiohydrolase and phosphatase were gradually reduced with increasing emersion time, while ß-xylosidase reduction was similar when emersion last for 7 or more days, and the phenol oxidase reduction was similar at 14 and 21days of leaf emersion. Microbial biomass and fungal sporulation were reduced after 21days of emersion. The structure of microbial assemblages was affected by the duration of the emersion period. The shifts in fungal assemblages were correlated with a decreased microbial capacity to degrade lignin and hemicellulose in leaf litter exposed to emersion. Additionally, some resilience was observed in leaf litter mass loss, bacterial biomass, some enzyme activities and structure of fungal assemblages. Our study shows that drought can strongly alter structural and functional aspects of microbial decomposers. Therefore, the exposure of leaf litter to increasing emersion periods in temperate streams is expected to affect decomposer communities and overall decomposition of plant material by decelerating carbon cycling in streams.

Responses of microbial decomposers to drought in streams may depend on the environmental context.

A consequence of drought in streams is the emersion of decomposing leaf litter, which may alter organic matter recycling. We assessed the effects of emersion on decomposition of black poplar leaves and associated microbes (microbial biomass, extracellular enzyme activities and microbial diversity) in two streams with distinct characteristics, in particular nutrients, temperature and oxygen levels. Leaf decomposition rates, fungal biomass and extracellular enzyme activities were lower in the most impacted stream (high nutrients and temperature, low oxygen). Also, the structure of fungal and bacterial communities differed between streams. Emersion strongly affected all microbial functional measures. Leaf decomposition, fungal biomass and extracellular enzyme activities were more sensitive at the most pristine site, while fungal reproduction and bacterial biomass production were more affected by emersion at the most impacted stream. Microbial community structure was strongly altered after emersion. Although similar effects on leaf-associated microbes were found in both streams, functional responses to emersion differed probably as a consequence of different initial microbial communities with different sensitivity to the drying stress. Our study highlights the need of understanding the effects of drought in streams suffering from different environmental perturbations, since responses to emersion appear to depend on the environmental context.

Quality and reactivity of dissolved organic matter in a Mediterranean river across hydrological and spatial gradients.

Understanding DOM transport and reactivity in rivers is essential to having a complete picture of the global carbon cycle. In this study, we explore the effects of hydrological variability and downstream transport on dissolved organic matter (DOM) dynamics in a Mediterranean river. We sampled the main stem of the river Tordera from the source to the sea, over a range of fifteen hydrological conditions including extreme events (flood and drought). By exploring spatial and temporal gradients of DOM fluorescence properties, river hydrology was found to be a significant predictor of DOM spatial heterogeneity. An additional space-resolved mass balance analysis performed on four contrasting hydrological conditions revealed that this was due to a shift in the biogeochemical function of the river. Flood conditions caused a conservative transport of DOM, generating a homogeneous, humic-like spatial profile of DOM quality. Lower flows induced a non-conservative, reactive transport of DOM, which enhanced the spatial heterogeneity of DOM properties. Moreover, the downstream evolution of DOM chemostatic behaviour revealed that the role of hydrology in regulating DOM properties increased gradually downstream, indicating an organised inter-dependency between the spatial and the temporal dimensions. Overall, our findings reveal that riverine DOM dynamics is in constant change owing to varying hydrological conditions, and emphasize that in order to fully understand the role of rivers in the global carbon cycle, it is necessary to take into account the full range of hydrological variability, from floods to droughts.

Warmer night-time temperature promotes microbial heterotrophic activity and modifies stream sediment community.

Diel temperature patterns are changing because of global warming, with higher temperatures being predicted to be more pronounced at night. Biological reactions are temperature dependent, with some occurring only during the daylight hours (e.g., light photosynthesis) and other during the entire day (e.g., respiration). Consequently, we expect the modification of daily temperature cycles to alter microbial biological reactions in stream sediments. Here, we aimed to study the effect of warming and changes of the diel temperature patterns on stream sediment biofilm functions tied to organic carbon decomposition, as well as on biofilm meiofaunal community structure. We performed an eight-week experiment with 12 artificial streams subjected to three different diel temperature patterns: warming, warmer nights and control. Significant effects of warming on biofilm function and structure were mainly detected in the long term. Our results showed that warming altered biofilm function, especially in the warmer nights' treatment, which enhanced ß-glucosidase enzyme activity. Interestingly, clear opposite diel patterns were observed for dissolved organic carbon and ß-glucosidase activity, suggesting that, at night, sediment bacteria quickly consume the input of photosynthetic dissolved organic carbon labile compounds created during light-time. The biofilm structure was also altered by warming, as both warming and warmer night treatments enhanced copepod abundance and diminished abundances of turbellaria and nematodes, which, in turn, controlled bacterial, algal and ciliate communities. Overall, we conclude that warming has strong effect on sediment biofilm structure and enhanced microbial organic matter degradation which might, consequently, affect higher trophic levels and river carbon cycling.

Differences in the sensitivity of fungi and bacteria to season and invertebrates affect leaf litter decomposition in a Mediterranean stream.

Microorganisms are key drivers of leaf litter decomposition; however, the mechanisms underlying the dynamics of different microbial groups are poorly understood. We investigated the effects of seasonal variation and invertebrates on fungal and bacterial dynamics, and on leaf litter decomposition. We followed the decomposition of Populus nigra litter in a Mediterranean stream through an annual cycle, using fine and coarse mesh bags. Irrespective of the season, microbial decomposition followed two stages. Initially, bacterial contribution to total microbial biomass was higher compared to later stages, and it was related to disaccharide and lignin degradation; in a later stage, bacteria were less important and were associated with hemicellulose and cellulose degradation, while fungi were related to lignin decomposition. The relevance of microbial groups in decomposition differed among seasons: fungi were more important in spring, whereas in summer, water quality changes seemed to favour bacteria and slowed down lignin and hemicellulose degradation. Invertebrates influenced litter-associated microbial assemblages (especially bacteria), stimulated enzyme efficiencies and reduced fungal biomass. We conclude that bacterial and fungal assemblages play distinctive roles in microbial decomposition and differ in their sensitivity to environmental changes, ultimately affecting litter decomposition, which might be particularly relevant in highly seasonal ecosystems, such as intermittent streams.

The ecology and biogeochemistry of stream biofilms.

Streams and rivers form dense networks, shape the Earth's surface and, in their sediments, provide an immensely large surface area for microbial growth. Biofilms dominate microbial life in streams and rivers, drive crucial ecosystem processes and contribute substantially to global biogeochemical fluxes. In turn, water flow and related deliveries of nutrients and organic matter to biofilms constitute major constraints on microbial life. In this Review, we describe the ecology and biogeochemistry of stream biofilms and highlight the influence of physical and ecological processes on their structure and function. Recent advances in the study of biofilm ecology may pave the way towards a mechanistic understanding of the effects of climate and environmental change on stream biofilms and the biogeochemistry of stream ecosystems.

Arsenic toxicity effects on microbial communities and nutrient cycling in indoor experimental channels mimicking a fluvial system.

The toxicity of chemicals in the environment is influenced by many factors, such as the adsorption to mineral particles, active biological surfaces, biotransformation and/or nutrient concentration. In the present study, a simplified fluvial system including fish, periphyton and sediment was used to investigate the fate and effects of environmentally realistic concentration of arsenic (As) on biofilm growth and nutrient cycling. Total dissolved arsenic concentration decreased exponentially from 120µg/L to 28.0±1.5µg/L during the experiment (60 days), mostly sinking to the sediment and a smaller percentage accumulated in the periphytic biofilm. Most P and N, which was provided by fish, was also retained in the epipsammic biofilm (growing on sediment grains). We conclude that exposure to this concentration of arsenic under oligotrophic conditions is changing the quality and quantity of the base of the aquatic food chain and its respective contribution to nutrient cycling, and normal functioning of the ecosystem. The effects include lowering the total biomass of biofilm and its potential ability to use organic P (i.e., phosphatase activity), inhibiting algal growth, especially that of diatoms, decreasing nitrogen content, and making the epipsammic biofilm more heterotrophic, thus reducing its ability to oxygenate the aquatic environment.

Consequences of warming and resource quality on the stoichiometry and nutrient cycling of a stream shredder.

As a result of climate change, streams are warming and their runoff has been decreasing in most temperate areas. These changes can affect consumers directly by increasing their metabolic rates and modifying their physiology and indirectly by changing the quality of the resources on which organisms depend. In this study, a common stream detritivore (Echinogammarus berilloni Catta) was reared at two temperatures (15 and 20°C) and fed Populus nigra L. leaves that had been conditioned either in an intermittent or permanent reach to evaluate the effects of resource quality and increased temperatures on detritivore performance, stoichiometry and nutrient cycling. The lower quality (i.e., lower protein, soluble carbohydrates and higher C:P and N:P ratios) of leaves conditioned in pools resulted in compensatory feeding and lower nutrient retention capacity by E. berilloni. This effect was especially marked for phosphorus, which was unexpected based on predictions of ecological stoichiometry. When individuals were fed pool-conditioned leaves at warmer temperatures, their growth rates were higher, but consumers exhibited less efficient assimilation and higher mortality. Furthermore, the shifts to lower C:P ratios and higher lipid concentrations in shredder body tissues suggest that structural molecules such as phospholipids are preserved over other energetic C-rich macromolecules such as carbohydrates. These effects on consumer physiology and metabolism were further translated into feces and excreta nutrient ratios. Overall, our results show that the effects of reduced leaf quality on detritivore nutrient retention were more severe at higher temperatures because the shredders were not able to offset their increased metabolism with increased consumption or more efficient digestion when fed pool-conditioned leaves. Consequently, the synergistic effects of impaired food quality and increased temperatures might not only affect the physiology and survival of detritivores but also extend to other trophic compartments through detritivore-mediated nutrient cycling.

Effects of warming on stream biofilm organic matter use capabilities.

The understanding of ecosystem responses to changing environmental conditions is becoming increasingly relevant in the context of global warming. Microbial biofilm communities in streams play a key role in organic matter cycling which might be modulated by shifts in flowing water temperature. In this study, we performed an experiment at the Candal stream (Portugal) longitudinally divided into two reaches: a control half and an experimental half where water temperature was 3 °C above that of the basal stream water. Biofilm colonization was monitored during 42 days in the two stream halves. Changes in biofilm function (extracellular enzyme activities and carbon substrate utilization profiles) as well as chlorophyll a and prokaryote densities were analyzed. The biofilm in the experimental half showed a higher capacity to decompose cellulose, hemicellulose, lignin, and peptidic compounds. Total leucine-aminopeptidase, cellobiohydrolase and ß-xylosidase showed a respective 93, 66, and 61% increase in activity over the control; much higher than would be predicted by only the direct temperature physical effect. In contrast, phosphatase and lipase activity showed the lowest sensitivity to temperature. The biofilms from the experimental half also showed a distinct functional fingerprint and higher carbon usage diversity and richness, especially due to a wider use of polymers and carbohydrates. The changes in the biofilm functional capabilities might be indirectly affected by the higher prokaryote and chlorophyll density measured in the biofilm of the experimental half. The present study provides evidence that a realistic stream temperature increase by 3 °C changes the biofilm metabolism to a greater decomposition of polymeric complex compounds and peptides but lower decomposition of lipids. This might affect stream organic matter cycling and the transfer of carbon to higher trophic levels.

Shifts in microbial community structure and function in light- and dark-grown biofilms driven by warming.

Biofilms are dynamic players in biogeochemical cycling in running waters and are subjected to environmental stressors like those provoked by climate change. We investigated whether a 2°C increase in flowing water would affect prokaryotic community composition and heterotrophic metabolic activities of biofilms grown under light or dark conditions. Neither light nor temperature treatments were relevant for selecting a specific bacterial community at initial phases (7-day-old biofilms), but both variables affected the composition and function of mature biofilms (28-day-old). In dark-grown biofilms, changes in the prokaryotic community composition due to warming were mainly related to rotifer grazing, but no significant changes were observed in functional fingerprints. In light-grown biofilms, warming also affected protozoan densities, but its effect on prokaryotic density and composition was less evident. In contrast, heterotrophic metabolic activities in light-grown biofilms under warming showed a decrease in the functional diversity towards a specialized use of several carbohydrates. Results suggest that prokaryotes are functionally redundant in dark biofilms but functionally plastic in light biofilms. The more complex and self-serving light-grown biofilm determines a more buffered response to temperature than dark-grown biofilms. Despite the moderate increase in temperature of only 2°C, warming conditions drive significant changes in freshwater biofilms, which responded by finely tuning a complex network of interactions among microbial populations within the biofilm matrix.

Assessment of multi-chemical pollution in aquatic ecosystems using toxic units: compound prioritization, mixture characterization and relationships with biological descriptors.

Chemical pollution is typically characterized by exposure to multiple rather than to single or a limited number of compounds. Parent compounds, transformation products and other non-targeted compounds yield mixtures whose composition can only be partially identified by monitoring, while a substantial proportion remains unknown. In this context, risk assessment based on the application of additive ecotoxicity models, such as concentration addition (CA), is rendered somewhat misleading. Here, we show that ecotoxicity risk information can be better understood upon consideration of the probabilistic distribution of risk among the different compounds. Toxic units of the compounds identified in a sample fit a lognormal probability distribution. The parameters characterizing this distribution (mean and standard deviation) provide information which can be tentatively interpreted as a measure of the toxic load and its apportionment among the constituents in the mixture (here interpreted as mixture complexity). Furthermore, they provide information for compound prioritization tailored to each site and enable prediction of some of the functional and structural biological variables associated with the receiving ecosystem. The proposed approach was tested in the Llobregat River basin (NE Spain) using exposure and toxicity data (algae and Daphnia) corresponding to 29 pharmaceuticals and 22 pesticides, and 5 structural and functional biological descriptors related to benthic macroinvertebrates (diversity, biomass) and biofilm metrics (diatom quality, chlorophyll-a content and photosynthetic capacity). Aggregated toxic units based on Daphnia and algae bioassays provided a good indication of the pollution pattern of the Llobregat River basin. Relative contribution of pesticides and pharmaceuticals to total toxic load was variable and highly site dependent, the latter group tending to increase its contribution in urban areas. Contaminated sites' toxic load was typically dominated by fewer compounds as compared to cleaner sites where more compounds contribute.