Alternative Stable States Driven by Density-Dependent Toxicity

Many populations are exposed to naturally occurring or synthetic toxicants. An increasing number of studies demonstrate that the toxicity of such compounds is not only dependent on the concentration or load, but also on the biomass or density of exposed organisms. At high biomass, organisms may be able to alleviate adverse effects of the toxicant by actively lowering ambient concentrations through either a joint detoxification mechanism or growth dilution. We show in a conceptual model that this mechanism may potentially lead to alternative stable states if the toxicant is lethal at low densities of organisms, whereas a high density is able to reduce the toxicant concentrations to sub-lethal levels. We show in an example that this effect may be relevant in real ecosystems. In an earlier published experimental laboratory study, we demonstrated that ammonia toxicity in eelgrass is highly dependent on the eelgrass shoot density. Here, we used the results of these experiments to construct a model describing the complex interactions between the temperate seagrass Zostera marina and potentially lethal ammonia. Analyses of the model show that alternative stable states are indeed present over wide ranges of key-parameter settings, suggesting that the mechanism might be important especially in sheltered, eutrophicated estuaries where mixing of the water layer is poor. We argue that the same mechanism could cause alternative stable states in other biological systems as well.     

Is erythroferrone finally the long sought-after systemic erythroid regulator of iron?

Iron metabolism is regulated on the cellular and the systemic level. Over the last decade, the liver peptide "hepcidin" has emerged as the body's key irons store regulator. The long postulated "erythroid regulator of iron", however, remained elusive. Last year, evidence was provided, that a previously described myokine "myonectin" may also function as the long sought erythroid regulator of iron. Myonectin was therefore renamed "erythroferrone". This editorial provides a brief discussion on the two functions of erythroferrone and also briefly considers the emerging potential role of transferrin receptor 2 in erythropoiesis.     

Genome sequences of Alicycliphilus denitrificans strains BC and K601T

Alicycliphilus denitrificans strain BC and A. denitrificans strain K601(T) degrade cyclic hydrocarbons. These strains have been isolated from a mixture of wastewater treatment plant material and benzene-polluted soil and from a wastewater treatment plant, respectively, suggesting their role in bioremediation of soil and water. Although the strains are phylogenetically closely related, there are some clear physiological differences. The hydrocarbon cyclohexanol, for example, can be degraded by strain K601(T) but not by strain BC. Furthermore, both strains can use nitrate and oxygen as an electron acceptor, but only strain BC can use chlorate as electron acceptor. To better understand the nitrate and chlorate reduction mechanisms coupled to the oxidation of cyclic compounds, the genomes of A. denitrificans strains BC and K601(T) were sequenced. Here, we report the complete genome sequences of A. denitrificans strains BC and K601(T).     

Analysis of the microbial community of the biocathode of a hydrogen-producing microbial electrolysis cell

The microbial electrolysis cell (MEC) is a promising system for hydrogen production. Still, expensive catalysts such as platinum are needed for efficient hydrogen evolution at the cathode. Recently, the possibility to use a biocathode as an alternative for platinum was shown. The microorganisms involved in hydrogen evolution in such systems are not yet identified. We analyzed the microbial community of a mixed culture biocathode that was enriched in an MEC bioanode. This biocathode produced 1.1 A m⁻² and 0.63 m³ H₂ m⁻³ cathode liquid volume per day. The bacterial population consisted of 46% Proteobacteria, 25% Firmicutes, 17% Bacteroidetes, and 12% related to other phyla. The dominant ribotype belonged to the species Desulfovibrio vulgaris. The second major ribotype cluster constituted a novel taxonomic group at the genus level, clustering within uncultured Firmicutes. The third cluster belonged to uncultured Bacteroidetes and grouped in a taxonomic group from which only clones were described before; most of these clones originated from soil samples. The identified novel taxonomic groups developed under environmentally unusual conditions, and this may point to properties that have not been considered before. A pure culture of Desulfovibrio strain G11 inoculated in a cathode of an MEC led to a current development from 0.17 to 0.76 A m⁻² in 9 days, and hydrogen gas formation was observed. On the basis of the known characteristics of Desulfovibrio spp., including its ability to produce hydrogen, we propose a mechanism for hydrogen evolution through Desulfovibrio spp. in a biocathode system.     

Nitrate and (per)chlorate reduction pathways in (per)chlorate-reducing bacteria

The reduction of (per)chlorate and nitrate in (per)chlorate-reducing bacteria shows similarities and differences. (Per)chlorate reductase and nitrate reductase both belong to the type?II DMSO family of enzymes and have a common bis(molybdopterin guanine dinucleotide)molybdenum cofactor. There are two types of dissimilatory nitrate reductases. With respect to their localization, (per)chlorate reductase is more similar to the dissimilatory periplasmic nitrate reductase. However, the periplasmic, unlike the membrane-bound, respiratory nitrate reductase, is not able to use chlorate. Structurally, (per)chlorate reductase is more similar to respiratory nitrate reductase, since these reductases have analogous subunits encoded by analogous genes. Both periplasmic (per)chlorate reductase and membrane-bound nitrate reductase activities are induced under anoxic conditions in the presence of (per)chlorate and nitrate respectively. During microbial (per)chlorate reduction, molecular oxygen is generated. This is not the case for nitrate reduction, although an atypical reaction in nitrite reduction linked to oxygen formation has been described recently. Microbial oxygen production during reduction of oxyanions may enhance biodegradation of pollutants under anoxic conditions.     

Does autophagy mediate age-dependent effect of dietary restriction responses in the filamentous fungus Podospora anserina?

Autophagy is a well-conserved catabolic process, involving the degradation of a cell''s own components through the lysosomal/vacuolar machinery. Autophagy is typically induced by nutrient starvation and has a role in nutrient recycling, cellular differentiation, degradation and programmed cell death. Another common response in eukaryotes is the extension of lifespan through dietary restriction (DR). We studied a link between DR and autophagy in the filamentous fungus Podospora anserina, a multicellular model organism for ageing studies and mitochondrial deterioration. While both carbon and nitrogen restriction extends lifespan in P. anserina, the size of the effect varied with the amount and type of restricted nutrient. Natural genetic variation for the DR response exists. Whereas a switch to carbon restriction up to halfway through the lifetime resulted in extreme lifespan extension for wild-type P. anserina, all autophagy-deficient strains had a shorter time window in which ageing could be delayed by DR. Under nitrogen limitation, only PaAtg1 and PaAtg8 mediate the effect of lifespan extension; the other autophagy-deficient mutants PaPspA and PaUth1 had a similar response as wild-type. Our results thus show that the ageing process impinges on the DR response and that this at least in part involves the genetic regulation of autophagy.     

A spatial model of climate change effects on yields and break‐even prices of switchgrass and miscanthus in Ontario,Canada

Concerns over global climate change have led many jurisdictions to implement strategies aimed at reducing greenhouse gas levels. One example is the replacement of coal with dedicated energy crops, such as switchgrass and miscanthus. The yields and costs of these potentially valuable bio‐energy crops have been evaluated in only a few cases, and previous studies have not focused on climate change effects. This article assesses the potential yields and costs of growing switchgrass and miscanthus on the agricultural land base in Ontario, Canada, under different climate assumptions, using a GIS‐based integrated biophysical and economic simulation model. The model shows that miscanthus has a mean peak yield that is 88.5% (29.6 t ha^?1 compared with 15.7 t ha^?1) higher and a mean farm gate break‐even price that is 25.9% ($58.20 per tonne compared with $73.29 per tonne) lower than switchgrass. The impact of climate change on the yield and break‐even price of switchgrass and miscanthus is dependent upon the climate model. CGCM3.1 predicts that mean peak yields of switchgrass and miscanthus could drop by 17.8% and 14.9%, whereas CCSM3.0 predicts that mean yields could increase to 41.4% and 44.9%, from 2071 to 2100, in the A2 climate scenario respectively. Both crops show promise as biomass sources for bio‐energy production, but a changing global climate, along with cultivar and planting technology developments, could affect crop choices.     

Ecological restoration of rich fens in Europe and North America: from trial and error to an evidence‐based approach

Fens represent a large array of ecosystem services, including the highest biodiversity found among wetlands, hydrological services, water purification and carbon sequestration. Land‐use change and drainage has severely damaged or annihilated these services in many parts of North America and Europe; restoration plans are urgently needed at the landscape level. We review the major constraints on the restoration of rich fens and fen water bodies in agricultural areas in Europe and disturbed landscapes in North America: (i) habitat quality problems: drought, eutrophication, acidification, and toxicity, and (ii) recolonization problems: species pools, ecosystem fragmentation and connectivity, genetic variability, and invasive species; and here provide possible solutions. We discuss both positive and negative consequences of restoration measures, and their causes. The restoration of wetland ecosystem functioning and services has, for a long time, been based on a trial‐and‐error approach. By presenting research and practice on the restoration of rich fen ecosystems within agricultural areas, we demonstrate the importance of biogeochemical and ecological knowledge at different spatial scales for the management and restoration of biodiversity, water quality, carbon sequestration and other ecosystem services, especially in a changing climate. We define target processes that enable scientists, nature managers, water managers and policy makers to choose between different measures and to predict restoration prospects for different types of deteriorated fens and their starting conditions.