Summary1. There is compelling evidence that anthropogenic disturbance can decrease biodiversity and impair ecological functioning. A major challenge to biodiversity-ecosystem function research is to disentangle the effects of biodiversity loss on ecosystem functions from the direct effects of human disturbance. 2. We studied the influence of human disturbance (acidification and eutrophication) and a natural stressor (low pH due to bedrock geology) on leaf-shredding macroinvertebrates, fungal decomposers and leaf decomposition rates in boreal streams. We used pyrosequencing techniques to determine fungal richness and assemblage structure. 3. Decomposition rates were higher in anthropogenically disturbed than in circumneutral reference or naturally acidic sites, but did not differ between the latter two groups. Macroinvertebrate richness was higher in circumneutral than in human-impacted or naturally acidic sites, and shredder evenness was highest in circumneutral sites. Fungal evenness was also lower in human-disturbed than in reference sites, whereas fungal richness did not vary among site groups. 4. Decomposition rate in fine-mesh bags was related positively to current velocity and fungal dominance, while in coarse-mesh bags, it was related positively to total phosphorus. In anthropogenically disturbed streams, the effects of low pH were overridden by eutrophication, and increased decomposition rates resulted from disturbance-induced increase in species dominance rather than richness. Furthermore, decomposition rates were positively correlated with abundances of dominant taxa, suggesting that ecosystem processes may be driven by a few key species. 5. Synthesis and applications. Our results suggest that leaf decomposition rates are insensitive to natural background variation, supporting the use of decomposition assays, preferably accompanied by molecular analysis of fungal assemblages, to assess stream ecosystem health. Instead of focusing solely on diversity, however, more emphasis should be placed at changes in dominance patterns, particularly if management aims are to improve stream ecosystem functioning.

Aim The perspective that microbial communities are controlled solely by environmental factors (‘everything is everywhere, but the environment selects’) has persisted for a long time, notwithstanding that recent studies have found that both environmental factors and spatial processes are important. We examined variation in the structure of fungal and bacterial communities in boreal streams along large local environmental gradients (e.g. stream size, acidity and nutrients) at intermediate spatial extent. Owing to the intermediate spatial extent of our study area and high dispersal rates of microbes, we expected that local environmental factors would structure stream fungal and bacterial communities. Location A set of 30 streams was sampled along a geographical transect from western to eastern Finland. Methods Leaf packs were used as sampling units in each stream. Fungal and bacterial operational taxonomic units (OTUs) were determined using pyrosequencing in the laboratory. Species accumulation curves were used to assess how well the regional species pools were sampled. Partial redundancy analysis and partial linear regression were used to determine the relative contributions of environmental and spatial variables to community structure and OTU richness, respectively. Results We found that environmental control was important in structuring fungal and bacterial communities, yet much of the variation was attributable to the shared effects of environmental and spatial predictors, or remained unexplained. The composition of fungal and bacterial communities was most strongly related to water chemistry variables (i.e. pH, aluminium and total phosphorus), whereas habitat variables (i.e. riparian deciduous trees, moss cover, substratum particle size and stream width) were clearly less important. We also found that fungal richness was negatively related to water iron concentration, whereas bacterial richness showed only a weak relationship with water pH. Main conclusions The composition and richness of stream microbial communities are mostly related to water chemistry variables at the spatial extent studied, emphasizing an important role for species sorting. This finding supports the traditional perspective that local environmental conditions are important drivers of variation in microbial communities. However, much of the variation in fungal and bacterial communities remained unexplained, suggesting that drivers of these communities are likely to be complex and not yet fully understood.

A β-class carbonic anhydrase (CA, EC 4.2.1.1) was cloned from the genome of the Monogenean platyhelminth Gyrodactylus salaris, a parasite of Atlantic salmon. The new enzyme, GsaCAβ has a significant catalytic activity for the physiological reaction, CO 2 + H 2 O ⇋ HCO 3 − + H + with a k cat of 1.1 × 10 5 s −1 and a k cat /K m of 7.58 × 10 6 M −1 × s −1 . This activity was inhibited by acetazolamide (K I of 0.46 µM), a sulphonamide in clinical use, as well as by selected inorganic anions and small molecules. Most tested anions inhibited GsaCAβ at millimolar concentrations, but sulfamide (K I of 81 µM), N,N -diethyldithiocarbamate (K I of 67 µM) and sulphamic acid (K I of 6.2 µM) showed a rather efficient inhibitory action. There are currently very few non-toxic agents effective in combating this parasite. GsaCAβ is subsequently proposed as a new drug target for which effective inhibitors can be designed.

A β-class carbonic anhydrase (CA, EC 4.2.1.1) present in the genome of the Monogenean platyhelminth Gyrodactylus salaris, a fish parasite, GsaCAβ, has been investigated for its inhibitory effects with a panel of sulphonamides and sulfamates, some of which in clinical use. Several effective GsaCAβ inhibitors were identified, belonging to simple heterocyclic sulphonamides, the deacetylated precursors of acetazolamide and methazolamide ( K I sof 81.9–139.7 nM). Many other simple benezene sulphonamides and clinically used agents, such as acetazolamide, methazolamide, ethoxzolamide, dorzolamide, benzolamide, sulthiame and hydrochlorothiazide showed inhibition constants <1 µM. The least effective GsaCAβ inhibitors were 4,6-disubstituted-1,3-benzene disulfonamides, with K I s in the range of 16.9–24.8 µM. Although no potent GsaCAβ-selective inhibitors were detected so far, this preliminary investigation may be helpful for better understanding the inhibition profile of this parasite enzyme and for the potential development of more effective and eventually parasite-selective inhibitors.