No abstract

Over the past 50 years, many millions of European honey bee (Apis mellifera) colonies have died as the ectoparasitic mite, Varroa destructor, has spread around the world. Subsequent studies have indicated that the mite's association with a group of RNA viral pathogens (Deformed Wing Virus, DWV) correlates with colony death. Here, we propose a phenomenon known as superinfection exclusion that provides an explanation of how certain A. mellifera populations have survived, despite Varroa infestation and high DWV loads. Next-generation sequencing has shown that a non-lethal DWV variant ‘type B' has become established in these colonies and that the lethal ‘type A' DWV variant fails to persist in the bee population. We propose that this novel stable host-pathogen relationship prevents the accumulation of lethal variants, suggesting that this interaction could be exploited for the development of an effective treatment that minimises colony losses in the future.

No abstract

A new strictly anaerobic bacterium (strain BAL-lT) has been isolated from a reed bed at Ballarat Goldfields in Australia. A number of different bacteria are able to protect themselves from arsenic. They do so by first reducing arsenate [As(V)] that has entered the cell to arsenite [As(III)] and then transporting the arsenite out of the cell; arsenate reduction does not appear to support growth (7,20). Reduction of arsenate to arsenite in anoxic environments has also been demonstrated (3, 15), but until recently the organisms responsible for this reduction and the mechanisms used were not known.

No abstract

Force-separation measurements between a deformable, rough, biological surface (Cryptosporidium parvum) and an inorganic oxide (silica) have been obtained using the atomic force microscope. The system was chosen because oocysts of C. parvum have been associated with waterborne outbreaks of disease, and one of the main barriers to oocyst contamination of drinking waters is provided by sand-bed filtration. The oocysts are shown to be significantly rough on the scale of Derjaguin-Landau-Verwey-Overbeek forces and have been found to be compressible on the scale of the loads applied during force measurement. The surface compressibility is reported in terms of an interfacial spring constant. The force of interaction prior to this Hookean region is long-range and repulsive. The long-range force has been compared to models of the electrical double layer force (based on the measured ζ-potentials and bulk electrolyte concentration) as well as an electrosteric force (treating the surface as a polyelectrolyte brush). The comparison has led to the conclusion that the surface can be described as a polyelectrolyte brush at intermediate separations (≈10-30 nm from linear compliance) with an electrical double layer often observed at greater separations. The dependence of the force on surface separation suggests that tethering between the oocyst and silica can occur. The variation of the interaction with pH and upon subtle changes in the ionic strength, compared to the variation from oocyst to oocyst, has also been assessed.

No abstract

The last 25 years have seen major advances in the field of mammalian genotoxicology, particularly with the advent of molecular methods, some of which have spilled over into the relatively new field of eco-genotoxicology, which aims to evaluate the impact of contaminants on the natural biota. Unlike mammalian genotoxicology, where the focus is centred on a limited number of model species, efforts in the marine field have generally lacked coordination and focus, with the result that progress has been somewhat slow and fragmented. However, it is recognized that at the DNA and chromosome levels, marine invertebrates express qualitatively similar types of induced damage to that found in higher organisms (e.g. point mutations, strand breaks and chromosomal aberrations). Given that many of these species (bivalve molluscs, crustaceans, polychaete worms, etc.) are linked directly or indirectly to the human food chain, this is an important reason why one should be concerned about their exposure to environmental mutagens and carcinogens, particularly as many of these organisms have the capacity to (i) transform these agents to biologically active metabolites and (ii) accumulate toxicants in their cells and tissues at concentrations several orders of magnitude above that found in the environment. This review covers the advantages and limitations of those cytogenetic and molecular assays that have been used to address the question of genotoxicity in the cells and early life stages of selected marine invertebrate species. It concludes with the recommendation for the adoption of standardized test procedures, leading to a tiered approach in future eco-genotoxicity testing.