From genes to genomes: beyond biodiversity in Spain's Rio Tinto.
(1/1318)
Spain's Rio Tinto, or Red River, an example of an extremely acidic (pH 1.7-2.5) environment with a high metal content, teems with prokaryotic and eukaryotic microbial life. Our recent studies based on small-subunit rRNA genes reveal an unexpectedly high eukaryotic phylogenetic diversity in the river when compared to the relatively low prokaryotic diversity. Protists can therefore thrive in and dominate extremely acidic, heavy-metal-laden environments. Further, because we have discovered protistan acidophiles closely related to neutrophiles, we can hypothesize that the transition from neutral to acidic environments occurs rapidly over geological time scales. How have these organisms adapted to such environments? We are currently exploring the alterations in physiological mechanisms that might allow for growth of eukaryotic microbes at acid extremes. To this end, we are isolating phylogenetically diverse protists in order to characterize and compare ion-transporting ATPases from cultured acidophiles with those from neutrophilic counterparts. We predict that special properties of these ion transporters allow protists to survive in the Rio Tinto. (+info)
Nitrogen uptake in riparian plant communities across a sharp ecological boundary of salmon density.
(2/1318)
BACKGROUND: Recent studies of anadromous salmon (Oncorhynchus spp.) on the Pacific Coast of North America indicate an important and previously unrecognized role of salmonid nutrients to terrestrial biota. However, the extent of this uptake by primary producers and consumers and the influences on community structure remain poorly described. We examine here the contribution of salmon nutrients to multiple taxa of riparian vegetation (Blechnum spicant, Menziesii ferruginea, Oplopanax horridus, Rubus spectabilis, Vaccinium alaskaense, V. parvifolium, Tsuga heterophylla) and measure foliar delta15N, total %N and plant community structure at two geographically separated watersheds in coastal British Columbia. To reduce potentially confounding effects of precipitation, substrate and other abiotic variables, we made comparisons across a sharp ecological boundary of salmon density that resulted from a waterfall barrier to salmon migration. RESULTS: delta15N and %N in foliage, and %cover of soil nitrogen indicators differed across the waterfall barrier to salmon at each watershed. delta15N values were enriched by 1.4 per thousand to 9.0 per thousand below the falls depending on species and watershed, providing a relative contribution of marine-derived nitrogen (MDN) to vegetation of 10% to 60%. %N in foliar tissues was slightly higher below the falls, with the majority of variance occurring between vegetation species. Community structure also differed with higher incidence of nitrogen-rich soil indicator species below the waterfalls. CONCLUSIONS: Measures of delta15N, %N and vegetation cover indicate a consistent difference in the riparian community across a sharp ecological boundary of salmon density. The additional N source that salmon provide to nitrogen-limited habitats appears to have significant impacts on the N budget of riparian vegetation, which may increase primary productivity, and result in community shifts between sites with and without salmon access. This, in turn, may have cascading ecosystem effects in forests adjacent to salmon streams. (+info)
High prevalence and morbidity of Schistosoma mansoni along the Albert Nile in Uganda.
(3/1318)
An epidemiological cross sectional study of Schistosoma mansoni was conducted in two hyper endemic fishing villages of Rhino Camp and Obongi both in West Nile district in northern Uganda in 1991 and 1992. People with various water contacts were registered. A small group of civil servants and clergies with less water contact in the river Nile were studied for control of infection and morbidity. An overall prevalence of 81.5% of the 1367 people studied in both fishing villages of Rhino Camp and Obongi were excreting from 100 to > or = 500 Schistosoma mansoni eggs per gram (epg). 253 18.5% did not have Schistosoma mansoni eggs in their faeces. The influence of socioeconomic factors on infections in the study population was high among poorer illiterates who have frequent water contacts activities with River Nile. The sonomorphological abnormalities of periportal thickening (PT) due to Schistosoma mansoni were performed using ultrasound. 664 patients were found to have various stages of (PT stages 0, I, II and III). A total of 703 (51.4%) patients did not have any periportal thickening (PT 0) in their livers despite the fact that 450 (32.9%) of them had Schistosoma. mansoni eggs in their faeces. The gravities of schistosomiasis in the two villages were similar showing greater morbidity in the younger adults. (+info)
Occurrence and antibiotic resistance of mesophilic Aeromonas in three riverine freshwaters of Marrakech, Morocco.
(4/1318)
In order to evaluate the impact of pollution and sewage on the occurrence and antibiotic resistance of mesophilic aeromonads in riverine freshwaters of Marrakech, samples were collected from three rivers (Oukaimeden, Ourika, and Tensift) upstream and downstream from the principal bordering villages. During a 2-year study, indicators of pollution increased dramatically in the downstream waters. Bacterial indicators (faecal coliforms and faecal streptococci) correlated with mesophilic aeromonads only in heavily polluted waters. In low and moderately polluted sources, densities of mesophilic aeromonads were independent of water quality indicators and did not correlate statistically with faecal indicators. Average counts of Aeromonas in low and heavily polluted waters were 2.5 x 10(3) and 2.1 x 10(6) colony forming units per 100 ml, respectively. The biochemical identification of 841 isolates indicated a predominance of A. caviae in heavily and moderately polluted water and sediment. A. hydrophila was dominant only in low polluted waters and when the temperature was below 12 degrees C. High densities of A. sobria were found in low, moderately polluted, or cleaned waters and when the water temperature was above 18 degrees C. All selected isolates (total = 841) were tested for antibiotic susceptibility against 21 antibiotics. Antibiotic resistance frequencies recorded were: ampicillin and amoxicillin, 100%; novobiocin, 96%; cefalotin, 81%; colistin, 72%; sulfamethoxazole, 40%; cefamandole, 37%; polymyxin B, 23%; trimethoprim, 17%; erythromycin, 15%; streptomycin, 8%; amoxicillin-clavulanate, 5%. Resistance to cefotaxime, kanamycin, gentamycin, chloramphenicol, tetracycline, oxytetracycline, nalidixic acid, rifampicin, or trimethoprim-sulfameth-oxazole was found to be <5%. Antibiotic resistance rates did vary according to the source of a strain"s isolation, and high numbers of antibiotic resistant strains were recorded in polluted samples. Since no correlation between mesophilic aeromonads and conventional faecal pollution indicators was observed in low or moderately polluted waters, and since these freshwaters are used for domestic supply, we propose the use of mesophilic aeromonads as complementary water pollution indicators to ensure the safety of water. (+info)
Plant functions in wetland and aquatic systems: influence of intensity and capacity of soil reduction.
(5/1318)
Wetland or hydric soils, in addition to excess water and limited air-filled porosity, are characterized by anaerobic or reducing conditions. Wetland plants have developed physiological and morphological adaptations for growing under these conditions. Various methods exist for measuring plant responses to reducing conditions in wetland and aquatic environments, including assessment of radial oxygen transport, cellular enzymatic transformations, changes in root structure, and nutrient uptake. However, a gap exists in quantifying the chemical properties and reducing nature of soil environment in which plant roots are grown. The variation in reducing conditions, oxygen demand, and other associated processes that occur in wetland soils makes it difficult to truly compare the plant responses reported in the literature. This review emphasizes soil-plant interactions in wetlands, drawing attention to the importance of quantifying the intensity and capacity of reduction and/or oxygen demand in wetland soils to allow proper evaluation of wetland plant responses to such conditions. (+info)
From litterfall to breakdown in streams: a review.
(6/1318)
This paper is a review of recent (< or =10 years) information on litterfall, standing stock of benthic organic matter, breakdown rates, and fungal colonization of organic matter in streams. In some cases, recent research reinforces the findings of classic reference papers. In other cases, the additional knowledge provided by recent research introduces a higher variation in the processes analyzed. In many aspects, especially those concerning stream organic matter, the review is biased towards the temperate North American streams, reflecting the fact that most research was carried out there. However, during the 1990s European studies increased enormously, especially those related with instream processes, such as leaf litter decomposition. The first part of this review analyzes the origin of allochthonous organic matter to streams (litterfall, retention, and storage), and it provides data on the amounts estimated in different streams and on the methodology used in the studies. The second part analyzes the fate of detritus in streams: mechanisms of leaf breakdown, relative importance of fungi and bacteria, factors affecting the activity of microbial decomposers, and chemical changes of leaf litter during decomposition. A list of breakdown rates of several different leaf species is given, together with the methodology used, and the main characteristics of the incubation streams. (+info)
Future trends in worldwide river nitrogen transport and related nitrous oxide emissions: a scenario analysis.
(7/1318)
We analyze possible future trends in dissolved inorganic nitrogen (DIN) export by world rivers and associated emissions of nitrous oxide (N2O). Our scenarios either assume that current trends continue or that nitrogen (N) inputs to aquatic systems are reduced as a result of changes in agriculture practices and fuel combustion technologies. The results indicate that moderate changes in the human diet in North America and Europe, reducing worldwide fertilizer use by only 16%, relative to Business-as-Usual (BAU) levels, may reduce DIN export rates to the North Atlantic and European Seas by about one third and associated N2O emissions by 36 to 77%. We furthermore calculate that relatively large reductions in NOy deposition rates in Europe (of about 80%) may reduce DIN export by rivers by a moderate 8% or less, relative to BAU levels. The potential effect of reduced NOy deposition on riverine DIN export is moderate, because most N in European rivers stems from agriculture, and not from fuel combustion. Nevertheless, the calculated 9% reduction (relative to BAU) in DIN inputs to the North Sea as a potential side effect of air pollution control may help achieve the international policy targets for reduced N inputs to the North Sea. (+info)
Nitrate leakage from deciduous forest soils into streams on Kureha Hill, Japan.
(8/1318)
Nitrate leakage from deciduous forest soils into streams was investigated for two adjacent hills. Many of the streams on Kureha Hill, located in Toyama City, Japan, have extremely high nitrate concentrations. The nitrate concentration of Hyakumakidani, one of the streams on Kureha Hill, averaged 158 microeq l(-1) and reached 470 microeq l(-1) during an episodic event. In contrast, the streams on Imizu Hill, adjacent to Kureha Hill, had low concentrations, below 15 microeq l(-1). Even during an episode, the nitrate concentrations increased to no more than 75 microeq l(-1). Both areas have similar blown forest soils, C/N ratios in O horizons, and vegetation consisting primarily of deciduous trees. However, soil incubation experiments, which lasted for 4 weeks, revealed that the nitrification rates in the surface soils of Kureha Hill were much higher than in the soils of Imizu Hill. (+info)