Autotrophic Biofilm Research Articles

Contribution of groundwater-borne nutrients to eutrophication potential and the share of benthic algae in a large lowland river

Groundwater inflow can be a significant source of nutrients for riverine ecosystems, which can affect eutrophication i.e., the elevated primary production and the corresponding accumulation of algal biomass. Experimental and modelling work has shown that benthic algae (autotrophic biofilms) in particular benefit, as they have direct access to the inflowing groundwater-borne nutrients. Primarily the supply of phosphorus (P) enhances pelagic algal biomass, as it is the limiting nutrient for primary production in most freshwater systems. In this study, we estimate the effect of groundwater inflow on overall eutrophication of a large, European lowland river and tested its seasonal effect on biofilms in particular. We calculated the effects on overall eutrophication during summer according to the estimated input of groundwater-borne P and the C:P stoichiometry of planktonic algae in the Elbe River. Our model indicated that these diffuse P inputs have the potential to significantly increase eutrophication. Groundwater-P can contribute up to 1.5 t/d PO4 over the investigated 450 km stretch of the Elbe River under low flow conditions. This would result in an additional planktonic load of about 46 t/d of particulate organic carbon, thereby contributing to eutrophication at the regional scale in this river. In contrast, at the local scale, biofilms were collected seasonally from artificial substrata exposed in the river either in hydrogeologically active areas with groundwater inflow, or in areas of varying hydraulic connectivity. Analyses of biofilm macronutrients, structural components and biofilm community composition show distinct effects of season, hydrogeology and groundwater inflow. The dominant predictors were season and the interaction between hydrogeology and groundwater. Benthic eutrophication is most likely to occur in autumn in areas of loose rock with high groundwater inflow. The strong interaction of environmental factors in determining benthic eutrophication highlights the need to assess these factors in combination rather than in isolation.

Autotrophic biofilms sustained by deeply sourced groundwater host diverse bacteria implicated in sulfur and hydrogen metabolism

BackgroundBiofilms in sulfide-rich springs present intricate microbial communities that play pivotal roles in biogeochemical cycling. We studied chemoautotrophically based biofilms that host diverse CPR bacteria and grow in sulfide-rich springs to investigate microbial controls on biogeochemical cycling.ResultsSulfide springs biofilms were investigated using bulk geochemical analysis, genome-resolved metagenomics, and scanning transmission X-ray microscopy (STXM) at room temperature and 87 K. Chemolithotrophic sulfur-oxidizing bacteria, including Thiothrix and Beggiatoa, dominate the biofilms, which also contain CPR Gracilibacteria, Absconditabacteria, Saccharibacteria, Peregrinibacteria, Berkelbacteria, Microgenomates, and Parcubacteria. STXM imaging revealed ultra-small cells near the surfaces of filamentous bacteria that may be CPR bacterial episymbionts. STXM and NEXAFS spectroscopy at carbon K and sulfur L2,3 edges show that filamentous bacteria contain protein-encapsulated spherical elemental sulfur granules, indicating that they are sulfur oxidizers, likely Thiothrix. Berkelbacteria and Moranbacteria in the same biofilm sample are predicted to have a novel electron bifurcating group 3b [NiFe]-hydrogenase, putatively a sulfhydrogenase, potentially linked to sulfur metabolism via redox cofactors. This complex could potentially contribute to symbioses, for example, with sulfur-oxidizing bacteria such as Thiothrix that is based on cryptic sulfur cycling. One Doudnabacteria genome encodes adjacent sulfur dioxygenase and rhodanese genes that may convert thiosulfate to sulfite. We find similar conserved genomic architecture associated with CPR bacteria from other sulfur-rich subsurface ecosystems.ConclusionsOur combined metagenomic, geochemical, spectromicroscopic, and structural bioinformatics analyses of biofilms growing in sulfide-rich springs revealed consortia that contain CPR bacteria and sulfur-oxidizing Proteobacteria, including Thiothrix, and bacteria from a new family within Beggiatoales. We infer roles for CPR bacteria in sulfur and hydrogen cycling.8FE2mu4H1cxgQVBqjGxsC2Video

Microbial race to colonise leaf litter in a littoral‐lake environment and its relation to nutrient dynamics

Abstract Litter colonisation by fungi and bacteria is essential for decomposition. Although algae are not directly related to the decomposition process, in lentic environment, they usually colonise leaf litter rapidly and stimulate the activity of heterotrophs. We hypothesised that the timing of litter entering the water determines a rapid colonisation by algae, which affects fungal and bacterial colonisation, nutrient dynamics of leaf litter, and decomposition rates. We incubated two leaf litter species, Nothofagus antarctica and Potentilla anserina, in the littoral zone of a lake under two conditions: submerged from the beginning (aquatic: AQ) and near the shoreline (initially terrestrial: T‐A). The T‐A treatment was flooded on day 44, so the decomposition process continued in aquatic conditions. We estimated two decomposition rates, one before day 42 (k42) and one for the whole incubation period (ka), algal and fungal biomass, bacterial abundance, and nutrient (P and N) content in leaf litter throughout the experiment. The timing of litter entering the water affected decomposition rates, k42 and ka were faster in AQ than in T‐A conditions and only the ka was faster in P. anserina than in N. antarctica. Microbial colonisation was also affected. Algal biomass was always higher in the AQ treatment, but bacterial abundance differed between treatments and changed through the decomposition process. Fungal biomass depended on both the treatment and the litter species. Bacterial–algal and fungal–algal relationships in AQ treatment were synergistic and independent of time, while, with terrestrial exposure, microbial relationships depended on the stage of the decomposition process. Nutrient dynamics depended on the treatment and the species, but both species tended to gain or maintain nutrient content throughout the experiment. Fungi were related to N:P changes through the decomposition process. Our results suggest that the conspicuous growth of an autotrophic biofilm on some litter (in P. anserina) might retard decomposition but at the same time stimulate heterotrophic colonisation. Therefore, the study of decomposition in the littoral zone of lakes must include the autotrophic component of biofilms that grow on detritus, since it alters organic matter consumption by decomposers and nutrient dynamics.

Short‐term effects of a large dam decommissioning on biofilm structure and functioning

Aging dams and the rising efforts to restore stream ecosystems are increasing the number of dam decommissioning programs. Although dam decommissioning aims at improving in‐stream habitat, biodiversity, and ecosystem functioning in the long term, it might also cause ecological impacts in the short term due to the mobilization of the sediment accumulated in the reservoir. Benthic biofilm in particular can be impaired by episodes of high turbidity and scouring. We conducted a multiple before‐after/control‐impact experiment to assess the effects of the drawdown of a large dam (42 m tall), a first step to its decommissioning, on biofilm structure (biomass and chlorophyll‐a) and functioning (metabolism, nutrient uptake, and organic matter breakdown). Our results show that the reservoir drawdown reduced the autotrophic biofilm biomass (chlorophyll‐a) downstream from the dam, which in turn lowered metabolism. However, nitrogen and phosphorus uptake by the biofilm was not affected. Organic matter breakdown was slower below the dam than in nearby undammed reaches before and during drawdown. All drawdown effects quickly disappeared and reaches downstream from the dam approached values found in nearby undammed reaches. Thus, our results indicate that the effects of reservoir drawdown on stream biofilms exist but may be small and disappear rapidly.

Microalgal food sources greatly improve macroinvertebrate growth in detritus‐based headwater streams: Evidence from an instream experiment

Abstract In forested headwater streams, inconspicuous food resources such as epilithic microalgae can play a major role owing to their content of long chain polyunsaturated fatty acids (PUFAs) that are essential for macroinvertebrate development. Yet, the use of these resources and their consequences for consumers and life‐history traits remain scarcely studied, especially for non‐herbivorous taxa. Using instream mesocosms, we aimed to understand how two macroinvertebrate species, a shredder detritivore (Gammarus pulex) and a scraper (Rhithrogena semicolorata), use available organic resources under light versus shaded conditions (high and low amounts of phototrophic biofilm, respectively). We specifically focused on the origin of carbon (C) and essential lipids (PUFAs, sterols) assimilated by the two species and the effects of these compounds on their survival and growth. When autotrophic biofilms were available (mesocosms exposed to light), both species experienced significantly higher growth than in mesocosms placed in the dark. In Rhithrogena nymphs, the survival and imago emergence rates were positively affected by access to autotrophic biofilms. Using stable isotope analysis (δ13C and δ15N), we demonstrated that under dark conditions both macroinvertebrates assimilated C of detrital origin. Under light conditions, most of the C assimilated by R. semicolorata was derived from autotrophic biofilms and around 11% from fine detrital particles (FPOM). Gammarus pulex derived part of its C from detrital sources (mainly FPOM) and from autotrophic biofilms. The results of isotopic analyses (δ13C) on fatty acids (FAs) and sterols showed that the scraper Rhithrogena was entirely dependent on autotrophic biofilms to meet its dietary FAs and sterol requirements. In contrast, detrital sources were quantitatively important for G. pulex both in terms of C and sterol supply, irrespective of the conditions tested. For these consumers, microalgae seemed to be a complementary food source, but yet essential to cover a large part of their requirements in long‐chain PUFAs. This study clearly confirmed the ecological importance of autotrophic biofilms for two functional feeding groups of macroinvertebrates in headwater streams providing new insights on the trophic origin of sterols and long‐chain PUFAs in their diet.

Analyzing the roles of cyclic dimeric guanosine monophosphate (c-di-GMP) on the formation of autotrophic granules and autotrophic biofilm in integrated fixed-film activated sludge (IFAS) reactor

This study is the first to reveal the important roles of c-di-GMP on the formation of autotrophic granular sludge (AUGS) and autotrophic biofilm (AUB) in integrated fixed-film activated sludge (IFAS) system. The results revealed that the partial nitrification/anammox (PN/A) performance was successfully developed in the IFAS system and high nitrogen removal efficiency was obtained. Notably, it was clearly indicated that the intracellular c-di-GMP content was highly linearly correlated with the concentration of protein (PN) in tightly bound extracellular polymeric substances (TB-EPS) during AUGS formation. It was also found that the c-di-GMP content was highly linearly correlated with the PN concentration during AUB formation, and also had a good linear correlation with the polysaccharide (PS) content in TB-EPS. This proves that intracellular c-di-GMP played a vital role in regulating the TB-EPS secretion, thereby further affecting the aggregation ability of AUGS and AUB. In addition, when the c-di-GMP regulates the content of PN in TB-EPS, the secondary structure of the PN also changes significantly correspondingly, affecting the hydrophobicity of AUGS and AUB. In long-term operation, Candidatus_Kuenenia, Nitrosomonas and Flavobacterium gradually became dominant species, which were considered to favor the formation of AUGS and AUB by promoting the production of c-di-GMP and TB-EPS.

Reduced N‐Limitation and Increased In‐Stream Productivity of Autotrophic Biofilms 5 and 15 Years After Severe Wildfire

AbstractThe ecosystem services provided by forests are under threat as wildfire frequency and severity increase throughout the western US. Severe wildfire can change physical environments and biogeochemical processes in watersheds with lasting effects on watershed nutrient cycling. For example, nitrate‐nitrogen (NO3‐N) export often increases following wildfire and can remain elevated for decades in severely burned watersheds. In this study, we investigated the effects of wildfire on stream biotic processing and watershed nutrient balance following two wildfires that burned along the Colorado Front Range. We evaluated stream water chemistry, nutrient limitation, benthic biomass, and stream metabolism along stream reaches within three burned and three unburned watersheds from July 26 to August 16, 2017. Although the two high‐severity wildfires occurred 5 and 15 years prior to the study, the streams draining burned watersheds still had 23‐times higher NO3‐N concentrations than unburned watersheds, a trend that is consistent across seasons and throughout the 15‐year post‐fire record. Autotrophic nitrogen (N) limitation was reduced in the nitrate‐rich burned streams. Consequently, autotrophic biomass and primary productivity were 2.5 and 20‐times greater, respectively, in burned relative to unburned streams. Together, these data suggest that N supply from burned uplands exceeded the increase in stream N demand and was the primary cause of chronic, elevated NO3‐N export from these severely burned watersheds. Accordingly, aquatic ecosystems within or downstream of burned watersheds may be susceptible to eutrophication and harmful algal blooms until vegetation recovery and plant nutrient demand reduce N supply to streams.

Autotrophic Fixed-Film Systems Treating High Strength Ammonia Wastewater.

The aim of the study was enrichment of nitrifying bacteria and to investigate the potential of autotrophic fixed-film and hybrid bioreactors to treat high strength ammonia wastewater (up to 1,000 mg N/L). Two types of fixed-film systems [moving bed biofilm reactor (MBBR) and BioCordTM] in two different configurations [sequencing batch reactor (SBR) and a continuous stirred tank reactor (CSTR)] were operated for 306 days. The laboratory-scale bioreactors were seeded with activated sludge from a municipal wastewater treatment plant and fed synthetic wastewater with no organics. Strategies for acclimation included biomass reseeding (during bioreactor start-up), and gradual increase in the influent ammonia concentration [from 130 to 1,000 mg N/L (10% every 5 days)]. Stable ammonia removal was observed up to 750 mg N/L from 45 to 145 days in the MBBR SBR (94–100%) and CSTR (72–100%), and BioCordTM SBR (96–100%) and CSTR (92–100%). Ammonia removal declined to 87% ± 6, in all bioreactors treating 1,000 mg N/L (on day 185). Following long-term operation at 1,000 mg N/L (on day 306), ammonia removal was 93–94% in both the MBBR SBR and BioCordTM CSTR; whereas, ammonia removal was relatively lower in MBBR CSTR (20–35%) and BioCordTM SBR (45–54%). Acclimation to increasing concentrations of ammonia led to the enrichment of nitrifying (Nitrosomonas, Nitrospira, and Nitrobacter) and denitrifying (Comamonas, OLB8, and Rhodanobacter) bacteria [16S rRNA gene sequencing (Illumina)] in all bioreactors. In the hybrid bioreactor, the nitrifying and denitrifying bacteria were relatively more abundant in flocs and biofilms, respectively. The presence of dead cells (in biofilms) suggests that in the absence of an organic substrate, endogenous decay is a likely contributor of nutrients for denitrifying bacteria. The nitrite accumulation and abundance of denitrifying bacteria indicate partial denitrification in fixed-film bioreactors operated under limited carbon conditions. Further studies are required to assess the contribution of organic material produced in autotrophic biofilms (by endogenous decay and soluble microbial products) to the overall treatment process. Furthermore, the possibility of sustaining autotrophic nitrogen in high strength waste-streams in the presence of organic substrates warrants further investigation.

Nitrifying biofilms deprived of organic carbon show higher functional resilience to increases in carbon supply

In nitrifying biofilms, the organic carbon to ammonia nitrogen (C/N) supply ratio can influence resource competition between heterotrophic and nitrifying bacteria for oxygen and space. We investigated the impact of acute and chronic changes in carbon supply on inter-guild competition in two moving bed biofilm reactors (MBBR), operated with (R1) and without (R0) external organic carbon supply. The microbial and nitrifying community composition of the reactors differed significantly. Interestingly, acute increases in the dissolved organic carbon inhibited nitrification in R1 ten times more than in R0. A sustained increase in the carbon supply decreased nitrification efficiency and increased denitrification activity to a greater extent in R1, and also increased the proportion of potential denitrifiers in both bioreactors. The findings suggest that autotrophic biofilms subjected to increases in carbon supply show higher nitrification and lower denitrification activity than carbon-fed biofilms. This has significant implications for the design of nitrifying bioreactors. Specifically, efficient removal of organic matter before the nitrification unit can improve the robustness of the bioreactor to varying influent quality. Thus, maintaining a low C/N ratio is important in nitrifying biofilters when acute carbon stress is expected or when anoxic activity (e.g. denitrification or H2S production) is undesirable, such as in recirculating aquaculture systems (RAS).

Biofilm Growth in Two Streams Draining Mountainous Permafrost Catchments in NE Greenland

AbstractThe objective of this study was to evaluate how stream water nutrient concentrations influence biofilm accrual in streams draining mountainous permafrost headwaters. We selected six stream locations in the Zackenberg area (NE Greenland, 74°N) subjected to a gradient in the areal contribution of different geomorphological units in the watersheds and channel stability. We used nutrient diffusing substrates to evaluate biofilm growth (autotrophic and total biomass). We found elevated stream nitrate concentrations in samples from upstream reaches draining larger areas of solifluction sheets and bare rock and with higher channel instability. Nitrate had the highest standardized effect on autotrophic biofilm growth on control disks. However, stream biofilm growth was not nutrient limited as shown by the absence of an increase in biofilm biomass as a response to the experimental nutrient additions. The response to nutrient additions via diffusing substrates depended on the altitude gradient. Overall, our results showed stream nitrogen availability to be one of the main drivers of algal biofilm accrual in high‐Arctic streams, suggesting that the predicted changes in nutrient exports induced by climate change will have strong impacts on the biogeochemistry and ecological functioning of high‐Arctic streams.

Purposely Designed Hierarchical Porous Electrodes for High Rate Microbial Electrosynthesis of Acetate from Carbon Dioxide.

Carbon-based products are crucial to our society, but their production from fossil-based carbon is unsustainable. Production pathways based on the reuse of CO2 will achieve ultimate sustainability. Furthermore, the costs of renewable electricity production are decreasing at such a high rate, that electricity is expected to be the main energy carrier from 2040 onward. Electricity-driven novel processes that convert CO2 into chemicals need to be further developed. Microbial electrosynthesis is a biocathode-driven process in which electroactive microorganisms derive electrons from solid-state electrodes to catalyze the reduction of CO2 or organics and generate valuable extracellular multicarbon reduced products. Microorganisms can be tuned to high-rate and selective product formation. Optimization and upscaling of microbial electrosynthesis to practical, real life applications is dependent upon performance improvement while maintaining low cost. Extensive biofilm development, enhanced electron transfer rate from solid-state electrodes to microorganisms and increased chemical production rate require optimized microbial consortia, efficient reactor designs, and improved cathode materials. This Account is about the development of different electrode materials purposely designed for improved microbial electrosynthesis: NanoWeb-RVC and EPD-3D. Both types of electrodes are biocompatible, highly conductive three-dimensional hierarchical porous structures. Both chemical vapor deposition (CVD) and electrophoretic deposition were used to grow homogeneous and uniform carbon nanotube layers on the honeycomb structure of reticulated vitreous carbon. The high surface area to volume ratio of these electrodes maximizes the available surface area for biofilm development, i.e., enabling an increased catalyst loading. Simultaneously, the nanostructure makes it possible for a continuous electroactive biofilm to be formed, with increased electron transfer rate and high Coulombic efficiencies. Fully autotrophic biofilms from mixed cultures developed on both types of electrodes rely on CO2 as the sole carbon source and the solid-state electrode as the unique energy supply. We present first the synthesis and characteristics of the bare electrodes. We then report the outstanding performance indicators of these novel biocathodes: current densities up to -200 A m-2 and acetate production rates up to 1330 g m-2 day-1, with electron and CO2 recoveries into acetate being very close to 100% for mature biofilms. The performance indicators are still among the highest reported by either purposely designed or commercially available biocathodes. Finally, we made use of the titration and off-gas analysis sensor (TOGA) to elucidate the electron transfer mechanism in these efficient biocathodes. Planktonic cells in the catholyte were found irrelevant for acetate production. We identified the electron transfer to be mediated by biologically induced H2. H2 is not detected in the headspace of the reactors, unless CO2 feeding is interrupted or the cathodes sterilized. Thus, the biofilm is extremely efficient in consuming the generated H2. Finally, we successfully demonstrated the use of a synthetic biogas mixture as a CO2 source. We thus proved the potential of microbial electrosynthesis for the simultaneous upgrading of biogas, while fixating CO2 via the production of acetate.

Light pollution enhances temporal variability of photosynthetic activity in mature and developing biofilm

Artificial light at night (ALAN) has been recently recognized as a threat for aquatic systems, but a comprehensive knowledge of its effects is still lacking. A fundamental question is whether and how ALAN might affect temporal variability of communities, thus undermining the stability of mature assemblages or influencing the colonization process. Here we investigated the role of ALAN on temporal variability of total biomass and maximum photosynthetic efficiency of marine autotrophic biofilms colonizing Mediterranean high-shore rock surfaces while controlling for density of their main grazers. Results showed stability in total biomass, but an increase in maximum photosynthetic efficiency from unlit to lit conditions, which suggested a temporal change in composition and/or abundance of different taxa within mature assemblages. The effect was weaker during the colonization process; in this case, density of grazers acted in the opposite direction of ALAN. We suggest that the addition of light at times when it would not be naturally present may affect the temporal variability of a variety of functioning in aquatic systems, depending on species-specific sensitivities to ALAN within microbial assemblages and/or indirect effects mediated by their consumers. We highlight to further investigate the role of this emergent topic in aquatic ecology.

Impact of Zirconium on Freshwater Periphytic Microorganisms

The majority of studies on biofilms have focused on autotrophic and bacterial taxa, without considering the potential effects on biofilm grazers. In this work, we investigated the effects of realistic environmental concentrations of zirconium (Zr) on periphyton algal growth and micromeiofauna biodiversity. Glass slides were submerged in a pond for four weeks to colonize biofilms and exposed for four weeks in aquaria to targeted Zr concentrations of 0, 1, and 10 nM, which were monitored over time (average measured concentrations were 0.2 ± 0.1, 0.5 ± 0.3, and 2.9 ± 0.3 nM Zr). The four-week exposure to the highest concentration (3 nM) affected the micromeiofauna structure of biofilms and modified the autotrophic biofilm structure by increasing the proportion of green algae and decreasing the abundance of cyanobacteria and brown algae. Rotifers and the ciliate Aspidisca cicada appeared to be the most sensitive organisms among the observed micromeiofauna. A toxic effect of Zr on rotifers could explain such results. Indirect effects, such as reduced food availability given the reduced algal growth in the presence of Zr, could also play a role in the changes of micromeiofauna community structure. These results are among the few published data on the effects of Zr.

Biofilm-specific uptake does not explain differences in whole-stream DOC tracer uptake between a forest and an agricultural stream

Benthic biofilms are often assumed to control terrestrially-derived dissolved organic carbon (tDOC) uptake in streams. We tested this by comparing 13C-enriched ryegrass leachate uptake in an agricultural and a forest stream, hypothesizing that a greater abundance of autotrophic biofilms in the agricultural stream would cause its whole-stream tDOC uptake to be comparatively low. We measured whole-stream and biofilm tDOC tracer uptake, metabolism, bacterial and algal diversity, and nutrient status of benthic epilithic biofilms, and assessed whole-stream hydromorphology. Whole-stream uptake of tDOC was six times lower in the agricultural (3.0 mg m−2 day−1) than in the forest (19.0 mg m−2 day−1) stream, and tDOC uptake velocity indicated lower tDOC demand in the agricultural (1.2 mm min−1) than in the forest (1.9 mm min−1) stream. The agricultural stream differed from the forest stream by slightly lower transient storage capacity and higher benthic biofilm bacterial abundance and production, lower biofilm biomass and lower biofilm molar C:N, C:P, and N:P ratios. Changes in epilithic biofilms contributed little to the differences in whole-stream tDOC tracer uptake between streams, as biofilm tDOC uptake only amounted to 4% and 13% of whole-stream uptake in the forest and agricultural stream, respectively. This comparison of a forest and an agricultural stream suggests that agricultural stressors have the potential to diminish both whole-stream tDOC uptake and uptake efficiency. Furthermore, the weak link between biofilm and whole-stream tDOC uptake implies that benthic biofilms characteristics are poor predictors for human impacts on tDOC uptake in agricultural streams and that hot spots of tDOC uptake are likely situated in the hyporheic zone or in the stream water column.

Interactive Impacts of Silver and Phosphorus on Autotrophic Biofilm Elemental and Biochemical Quality for a Macroinvertebrate Consumer.

Autotrophic biofilms are complex and fundamental biological compartments of many aquatic ecosystems. In particular, these biofilms represent a major resource for many invertebrate consumers and the first ecological barrier against toxic metals. To date, very few studies have investigated the indirect effects of stressors on upper trophic levels through alterations of the quality of biofilms for their consumers. In a laboratory study, we investigated the single and combined effects of phosphorus (P) availability and silver, a re-emerging contaminant, on the elemental [carbon (C):nitrogen (N):P ratios] and biochemical (fatty acid profiles) compositions of a diatom-dominated biofilm initially collected in a shallow lake. We hypothesized that (1) P and silver, through the replacement of diatoms by more tolerant primary producer species, reduce the biochemical quality of biofilms for their consumers while (2) P enhances biofilm elemental quality and (3) silver contamination of biofilm has negative effects on consumers life history traits. The quality of biofilms for consumers was assessed for a common crustacean species, Gammarus fossarum, by measuring organisms’ survival and growth rates during a 42-days feeding experiment. Results mainly showed that species replacement induced by both stressors affected biofilm fatty acid compositions, and that P immobilization permitted to achieve low C:P biofilms, whatever the level of silver contamination. Gammarids growth and survival rates were not significantly impacted by the ingestion of silver-contaminated resource. On the contrary, we found a significant positive relationship between the biofilm P-content and gammarids growth. This study underlines the large indirect consequences stressors could play on the quality of microbial biomass for consumers, and, in turn, on the whole food web.

Comprehensive evaluation of autohydrogenotrophic membrane biofilm reactor treating OTC-enriched water medium.

In the recent years, there has been considerable debate about the potential impacts of antibiotics present in various environments on the public health and ecology. Oxytetracycline (OTC) is one of tetracycline antibiotic group used for growth and treatment of animals and humans. In this study, OTC and nitrate (NO3-N) were simultaneously reduced using a hydrogen-based membrane biofilm reactor (H2-MBfR). The system successfully accomplished OTC and nitrate removals. The fluxes of OTC and NO3-N were 8.96mg OTC/m2day and 1100mgN/m2day, respectively. On the other hand, the fluxes of H2 utilized for OTC and NO3-N reductions were calculated as maximum values of 1.71 and 395mgH2/m2day, respectively. The concentrations of transformation products of OTC formed at ppb levels. The dominant species in all the experimental periods with OTC biodegradation referred to Naxibacter sp., Uncultured Beta proteobacterium, Janthinobacterium sp. and Alicycliphilus denitrificans in autotrophic biofilm community degrading OTC.

Comparison of biocides, allelopathic substances and UV-C as treatments for biofilm proliferation on heritage monuments

Abstract UV-C and biocide treatments are frequently used to treat historical monuments contaminated by autotrophic biofilms. In this study, the authors compare for the first time the efficacy of these treatments against microorganisms such as cyanobacteria and algae proliferating in the Vicherey church (Vicherey, Vosges Department, France). To identify the most environmentally friendly and also efficient method, an allelopathic treatment was also tested. Colorimetric and physiological measurements of treated biofilms were thus monitored for 6 months. Fungi growing on necrotic matter from treated biofilms were sampled and sequenced. With biocides, results showed incomplete eradication of biofilms, even after two treatments. Biofilm color loss was delayed in comparison to UV-C treatment, which appeared more efficient after just one treatment. Moreover, quantum yield (Fv/Fm) decreased immediately after UV-C treatment, indicating inhibition of algae and cyanobacteria photosynthesis. However, two species of fungi colonized the cyanobacteria biofilms treated with UV-C. Allelopathic treatment was not efficient on biofilm and showed no deleterious effect on photosynthesis. The present findings demonstrate that the UV-C method, coupled with a cleaning phase for necrotic organic matter, may be considered environmentally friendly and the best alternative to chemicals.

On a free boundary problem for biosorption in biofilms

The work presents the qualitative analysis of the free boundary value problem related to the biosorption process in multispecies biofilms. In the framework of continuum biofilm modeling, the mathematical problem consists of a system of nonlinear hyperbolic partial differential equations for microbial species growth and spreading, a system of semilinear parabolic partial differential equations describing the substrate trends and a system of semilinear parabolic partial differential equations accounting for the diffusion, reaction and biosorption of different agents on the various biofilm constituents. Two systems of nonlinear hyperbolic partial differential equations have been considered as well for modeling the dynamics of the free and bounded sorption sites. The free boundary evolution is regulated by a nonlinear ordinary differential equation. Overall, this leads to a free boundary value problem essentially hyperbolic. The main result is the existence and uniqueness of the solutions to the stated free boundary value problem, which have been derived by converting the partial differential equations to Volterra integral equations and then using the fixed point theorem. Moreover, the work is completed with numerical simulations for a real case examining the growth of a heterotrophic–autotrophic biofilm devoted to wastewater treatment and acting as a sorbing material for heavy metal biosorption.

Use of Nonsteady-state Biofilm Model to characterize heterotrophic and autotrophic biomass within aerobic granules

A pseudo-analytical solution for a Nonsteady-state Biofilm Model (NSBM) was used to describe heterotrophic and autotrophic biofilms within aerobic granules. This model was validated with the experimental results obtained from a granule-based SBR process that removes organics and ammonia simultaneously. The calibrated model (with boundary conditions including involved species, operating conditions, granular characteristics and biological reactions) predicted effluent COD and NH4 values that were in good agreement with the measured values. The model simulation showed that the increase of the substrate concentration did not dramatically influence the flux trends if the biomass concentration in the reactor is insufficient (less than 1000 mg VSS/L). The heterotrophic and autotrophic biofilms develop layer by layer on the outside of the aerobic granules. These can form simultaneously in independent patterns for substrate utilization and biomass growth. The NSBM could be an effective prediction method for the understanding of aerobic granulation.

Efficient nitrogen removal by simultaneous photoelectrocatalytic oxidation and electrochemically active biofilm denitrification

A novel nitrogen removal strategy, the combined photoelectrocatalytic oxidation and autotrophic biofilm denitrification, was developed to achieve simultaneous NH4+-N oxidation and NO3−-N reduction in a single reactor. AgI/TiO2-NTs and autotrophic denitrifying biofilm were used as anode and cathode, respectively. NH4+-N oxidation efficiency was enhanced by 3 times after the introduction of visible light. Moreover, NO3−-N and NO2−-N generated in the process of NH4+-N oxidation could be further removed by biocathode. Applied voltage and pH have significant effects on nitrogen removal. The NO3−-N and NH4+-N removal efficiencies gradually increased from 27.2% to 74.3% and 60.0% to 83.1%, respectively, when the voltage increased from 1.0V to 3.0V. Neutral or slightly alkaline condition was favorable on account of the autotrophic denitrifying biofilm. The optimum TN (TNNH4+-N+NO3−-N+NO2−-N) removal efficiency was up to 89.6% at pH 8 with 3.0V voltage.