The purification and properties of a thiaminase I enzyme from nardoo (Marsilea drummondii)

Fronds of the fern nardoo (Marsilea drummondii) contain a thiaminase I enzyme at very high levels of activity. Highest levels of enzyme activity were found in vigorously growing plant material. The thiaminase I has been purified to a final sp act value of 2.07 μkat/mg protein at 30° and pH 6.5. It was shown to have similar properties to thiaminase I enzymes purified from bracken fern, rock fern and freshwater mussels. These enzymes have MW values in the range 93 000–115 000, energies of activation of 14 000 cal mol, pH optima of 8–9 and are quite stable in the pH range 3 to 12 and to extended incubation at 55°. The temperature for 50 % denaturation is 60–65°. p-CMB, mersalyl acid and HgCl₂ (10^t-6 M) are potent inhibitors, but monoiodacetic acid (10^?4 M) has no effect. A wide range of heterocyclic bases, sulphydryl compounds, and amines, including the non-aromatic amines 6-aminohexanoic acid and ethanolamine, act as co-substrates in the thiaminase I reaction; however, their effectiveness is dependent on both their degrees of basicity and to some extent, their stereochemistry. When the co-substrate activity of a range of substituted anilines were compared, no correlation was found between the degree to which the base activates the reaction and the pK_b (or Hammett's sigma constant) of the base.     

Impact of a dam on benthic macroinvertebrates in a small river in a biodiversity hotspot: Cape Floristic Region, South Africa

Suitable reservoirs and monitoring methods are needed to manage scarce water supplies in dry countries. We assessed here the impact on aquatic macroinvertebrates of the only dam on the Eerste River, which runs through the heart of a biodiversity hotspot, the Cape Floristic Region, South Africa. The dam and associated activities, were the only forms of disturbance in this otherwise pristine area. We sampled over 20,000 macroinvertebrate individuals and illustrated some categorical effects of the impoundment and its effects on macroinvertebrate assemblages. Macroinvertebrate species diversity below the dam was only half of that in the pristine catchment area above the dam. Furthermore, Ephemeroptera, Plecoptera and Trichoptera diversity and abundance dropped to almost zero as a result of the impoundment. In contrast, the abundance of the Diptera family Chironomidae increased substantially below the dam. These changes in macroinvertebrate diversity mirrored those recorded in biologically less diverse areas, but are of major concern in this biodiversity hotspot with its rich endemic fauna. We conclude that such an impoundment, while important for human welfare, results in a high price being paid in terms of loss of local biodiversity.     

Effect of inducers of lipid peroxidation on the behavior of ciliated epithelial cells

Television microscope and original image treatment system were used for monitoring and recording the ciliary activity (beat frequency) of gill ciliated epithelia of the mussel Mytilus edulis (Bivalvia) and of the rat tracheal ciliated epithelia in response to the following prooxidants: H₂O₂, Fe⁺², Fe⁺² + ascorbic acid and NADP-H + ADP + Fe⁺². Mussel ciliated cells proved to be more sensitive to the influence of the prooxidants than rat cells. The reactions of ciliated epithelial cells of mollusks and rats to the inducers of lipid peroxidation were not similar to behavioral responses of these cells under the action of low-dose ionizing radiation.     

Wetlands and mosquitoes: a review

This review brings together information on mosquitoes, the diseases they transmit and the wetlands that provide habitats for the immature stages (eggs and larvae). Wetland values are mentioned, though the main literature on this does not generally overlap the mosquito issue. Mosquito management is overviewed to include: the use of larvicides, source reduction in intertidal wetlands and management in freshwater systems. There is not a great deal of information on mosquitoes and freshwater systems, except for constructed wetlands and they are considered separately. We then consider restoration mainly in the context of wetlands that have been the subject of habitat modification for mosquito control. Land use and climate change, as they affect mosquitoes and the diseases they transmit, are also reviewed, as this will affect wetlands via management activities. Finally the review addresses the critical issue of balancing health, both human and environmental, in an adaptive framework. It concludes that there is a need to ensure that both mosquito and wetland management communicate and integrate to sustain wetland and human health.     

Effects of temperature and stocking density on intensive culture of Pacific white shrimp in freshwater

In aquaculture, the application of predictive techniques based on statistical-mathematical modeling allows not only to project and study individual growth trajectories, but also to evaluate the probable effect of external factors that would explain their behavior over time. This is the case of this work, which takes the above as a principle to demonstrate the effect of water temperature on the growth of the Pacific white shrimp Litopenaeus vannamei cultured in fresh water (0 mg L⁻¹), using densities of 90, 120, 180, 230, 280 and 330 shrimp m⁻². Shrimp were exposed to water temperature between 11.5 °C and 31.6 °C. Temperature effect was determined using a parameterized Gompertz growth model with experimental data from each initial culture density. The best shrimp productivity yield was obtained above 26 °C, and the least efficient was below 22 °C. Densities of 90–180 shrimp m⁻² and 230–330 shrimp m⁻² generated a maximum average size of 12.6 g and 8.8 g in 30 weeks, respectively. Here we present the implications of the effect of water temperature on the intensive culture of white shrimp with zero salinity (0 mg L⁻¹) using these techniques from a predictive analytical approach.     

Influence of abiotic factors on bacterial proliferation and anoxic survival of the sea mussel Mytilus edulis L.

The effect of several abiotic factors (salinity, temperature and pH) on bacterial proliferation and survival time of the sea mussel Mytilus edulis L. were studied under anoxic incubations. In addition, the presence in the incubation media of ammonium and the volatile fatty acids propionate and acetate, both excreted fermentation products of the bivalve, was tested.Anoxic incubations with seawater diluted with demineralised water showed at the lowest salinity (50% seawater, SW) a significant increase in the capacity of M. edulis to survive anoxia as compared to both 75% SW and control [100% SW, corresponding to 32 practical salinity units (psu)]. Formation of biotic sulphide and ammonium occurred in all incubations. However, bacterial proliferation was postponed by 2-3 days at lowest salinity and accordingly, concentrations of both compounds were lower. Anoxic survival profiles of mussels collected from different habitats in the Dutch Scheldt area, characterised by differences in salinity (range from 17 to 31 psu), corresponded with the above salinity effect. Walsoorden mussels (17 psu) showed the longest (P<0.001) survival time under anoxia (LT₅₀=17.2 days) as compared with Paulina (27 psu) and Wemeldinge (31 psu) mussels (LT₅₀=12.8 and 9.8 days, respectively). Condition index (ratio of soft body weight to shell volume) was not correlated with anoxic survival time in untreated mussels, although this was clearly the case when the antibiotic chloramphenicol was added to the anoxic seawater.Acidification of the anoxic incubation medium had a positive effect on survival time. LT₅₀ values significantly (P<0.001) increased from 10.2 days at pH 8.1 to 11.6 and 11.5 days at pH 7.3 and 6.5, respectively. Biotic sulphide and ammonium accumulation as well as bacterial numbers were significantly lower at pH 7.3 and 6.5 as compared with pH 8.1. Anoxic incubations at 10 °C (LT₅₀=12.0 days) strongly increased survival time as compared to 18 °C (LT₅₀=5.9 days). The benefit of antibiotic addition was also stronger at lower temperature (10 °C).Addition of both propionate and acetate (0.5 mM) displayed no effect on mortality of mussels under anoxia, but ammonium (0.5 mM) caused a negative effect (P<0.001). Biotic sulphide and ammonium concentrations measured in both volatile fatty acid incubations were lower than the control situation, as well as total bacterial numbers.This study shows that environmental factors play a significant role in determining the course of bacterial infection and death of bivalves exposed to anoxia.     

Current knowledge of Chytridiomycota diversity in Northern Europe and future research needs

Chytridiomycota is the most species-rich phylum of basal lineage fungi involved in vital processes in both terrestrial and aquatic ecosystems. Still, the diversity and richness of this group remains cryptic. In Northern Europe, few species have been recorded despite the numerous intact lake systems covering this region. Recent classifications of early diverging fungal lineages differ considerably on the diversity of chytrid species and their taxonomic placement. Here, we present the current knowledge of the Chytridiomycota diversity within Northern Europe by using the Global Biodiversity Information Facility (GBIF) data and compare how this diversity distributes across two recently proposed classification systems. Furthermore, we illustrate how various sampling types are influencing the recorded classification levels. Lastly, we discuss how metabarcoding has contributed to the overall understanding of the Chytridiomycota diversity in revealing the “dark matter fungi”, and we point out future research needs in the field of aquatic mycology in the Nordic region.     

DISTRIBUTION AND DIVERSITY OF MKUZE SWAMP FISHES DURING A SUMMER FLOOD

SUMMARY

Very little information is available on the fishes of the Mkuze swamps and this paper presents the results of an ichthyofaunal survey conducted in March 1988. The study, which coincided with a major river flood, determined that the fish fauna was considerably more diverse than expected and 25 species were collected from 31 localities. Several distinct communities are recognized including a river channel/floodplain community, lagoonal community, feeder stream community and lower swamp community. The subtraction of tropical freshwater fish species in the region is documented and a complete checklist for the Mkuze River system, including several new records from this survey, is presented.     

Dramatic decline of two freshwater killifishes,main anthropogenic drivers and appropriate conservation actions

Freshwater fish biodiversity loss in the Mediterranean Basin is regarded as among the highest globally, with long-term population data sets required to discern long-term population trends of threatened species, in order to design appropriate conservation interventions. In this study, we assessed the population trends of two threatened freshwater fishes, Valencia letourneuxi and Valencia robertae, employing the most recent and largest compiled database to date (16 populations over 14 years). We applied the innovative methodology of the Living Planet Index (LPI) to assess the average rate of change over time across a set of V. letourneuxi and V. robertae populations in Greece. The LPI application revealed a dramatic decline of both species, with V. letourneuxi declining by 97.7% and V. robertae by 91.0%. Beta regression showed that water pollution, eutrophication and alien Eastern mosquitofish Gambusia holbrooki’ presence were the three best fitting predictors of the decline of V. letourneuxi and V. robertae populations. Based on the above, we outline the conservation measures urgently required to revert the near collapse of the populations of the two species. Conservation actions include the strict protection of the their lowland spring habitats, habitat improvement through changes in water management and agricultural practices, mosquitofish invasion prevention and mosquitofish impact mitigation measures, as well as translocation actions and captive breeding. Lastly, the association patterns of the proposed conservation actions with anthropogenic pressures and their expected outcomes were analysed through an alluvial diagram, providing insights on the scale of pressures mitigated by conservation actions and on their conservation benefits.     

Impairment of nucleoid segregation and cell division at high osmolarity in a strain of Escherichia coli overproducing the chaperone DnaK

Abstract Fourteen species of ciliates, seven of which are new, were found living in a sample of anoxic water collected from a small lake in Spain. The species belong to all six orders in which anaerobic ciliates have been described and they include the first anaerobic representatives of the order Prostomatida. This surprising diversity is probably sustained because it embraces all ciliate feeding types, and because protozoa are the only important consumers of the diversity of microbes in anoxic habitats. Six of the anaerobic ciliate species have aerobic congeners; this strengthens the contention that anaerobic ciliates evolved independently from aerobes belonging to several taxonomic groups.