Risk assessment for aflatoxins in foodstuffs

There had been a growing body of circumstantial evidence that aflatoxin B₁ is carcinogenic, as well as acutely toxic, to humans, but in 1987 that International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) accepted that aflatoxin should be classified as a Group 1 carcinogen. Regulatory levels set by the governments of many countries are based on the premise that aflatoxin is indeed carcinogenic and the European Community agreed on 16 July 1998 a limit of 2 μg kg⁻¹ for aflatoxin B₁ in a range of foods for human consumption. The need for a risk assessment arises from the widespread occurrence of the aflatoxins in commodities resulting from contamination in storage and in the field by the fungi which produce it—Aspergillus flavus, A. parasiticus and A. nomius. Risk assessment requires both a knowledge of exposure and a detailed knowledge of the toxicology of the aflatoxins. The toxicology of aflatoxin B₁ involves a complex sequence of metabolic alterations of the molecule by enzymes in the animal tissues (usually the liver). This complexity is reflected in the very diverse range of responses by different animal species and it is likely that there will also be differences in response amongst different races of humans, and indeed even amongst different individuals of the same race.     

A Geochemical Trophic Cascade in Yellowstone's Geothermal Environments

We contrast the geochemistry of the Madison drainage, which has high concentrations of geothermal features, with the Lamar drainage of Yellowstone National Park, USA, and trace the consequences of geochemical differences through abiotic and biotic linkages in the ecosystem. Waters in the geothermal-dominated drainage contained anomalously high levels of fluoride (F) and silica (SiO₂). Soils, stream sediments, and surface waters that interact or mix with geothermal waters, in turn, had elevated F and SiO₂ concentrations compared to similar samples from the Lamar drainage. The geochemical differences were reflected in the chemistry of forage plants, with some plants from geothermally influenced areas containing four- to eightfold higher concentrations of F and SiO₂ than similar plants in the Lamar drainage. Geothermal heat reduced snowpack, and we found that elk (Cervus elaphus) concentrated in these refugia as snowpack increased each winter. The consequent high dietary intake of F in animals associated with the geothermal areas was confirmed by the finding that bone samples from elk living in the Madison drainage contained sixfold higher concentrations of F than samples collected from animals wintering in the Lamar drainage. High F exposure resulted in compromised dentition due to fluoride toxicosis, which was undoubtedly exacerbated by the abrasive action of silica. The consequent accelerated and aberrant tooth wear resulted in early onset of senescence, reduced life span, and an abbreviated age structure. We speculate that these altered demographics, combined with spatial heterogeneity of snowpack, will result in increased vulnerability of this large herbivore population to wolf predation and less resiliency to compensate demographically for predation. Received 2 November 2001; accepted 27 February 2002.     

An ecological cost of plant defence: attractiveness of bitter cucumber plants to natural enemies of herbivores

Plants produce defences that act directly on herbivores and indirectly via the attraction of natural enemies of herbivores. We examined the pleiotropic effects of direct chemical defence production on indirect defence employing near‐isogenic varieties of cucumber plants (Cucumis sativus) that differ qualitatively in the production of terpenoid cucurbitacins, the most bitter compounds known. In release–recapture experiments conducted in greenhouse common gardens, blind predatory mites were attracted to plants infested by herbivorous mites. Infested sweet plants (lacking cucurbitacins), however, attracted 37% more predatory mites than infested bitter plants (that produce constitutive and inducible cucurbitacins). Analysis of the headspace of plants revealed that production of cucurbitacins was genetically correlated with large increases in the qualitative and quantitative spectrum of volatile compounds produced by plants, including induced production of (E )‐β‐ocimene (3E )‐4,8‐dimethyl‐1,3,7‐nonatriene, (E,E)‐α‐farnesene, and methyl salicylate, all known to be attractants of predators. Nevertheless, plants that produced cucurbitacins were less attractive to predatory mites than plants that lacked cucurbitacins and predators were also half as fecund on these bitter plants. Thus, we provide novel evidence for an ecological trade‐off between direct and indirect plant defence. This cost of defence is mediated by the effects of cucurbitacins on predator fecundity and potentially by the production of volatile compounds that may be repellent to predators.     

Large, tissue-regulated domain diversity of heparan sulfates demonstrated by phage display antibodies.

Heparan sulfates (HS) are long, linear polysaccharides with a high degree of variability. They bind to a vast number of proteins such as growth factors and cytokines, and these interactions are likely to be mediated by specific HS domains. To investigate the structural diversity and topological distribution of HS domains in tissues, we selected a panel of 10 unique anti-HS antibodies using phage display technology. All 10 antibodies recognize a specific HS epitope as demonstrated by enzyme-linked immunosorbent assay using defined synthetic HS oligosaccharides, modified HS/heparin molecules, and HS isolated from a variety of organs. The chemical groups involved in the epitopes could be indicated and the position of sulfate groups is of major importance. All HS epitopes have a defined tissue distribution as shown by immunohistochemistry using rat organs. Taken together, the data show that in vivo, a large number of defined HS epitopes exist that do not occur randomly but are tightly, topologically regulated.     

Survival and change in physiological state of Bradyrhizobium japonicum in soybean (Glycine max L. Merril) liquid inoculants after long-term storage

Commercial liquid inoculants for soybean, stored at 20 °C for 1–8 years in 400 ml bottles or in 5000 ml containers, were assessed for their efficacy and changes in the physiological activity of Bradyrhizobium japonicum. A decrease in viable counts and in bacterial survival on seeds was observed in inoculants stored for several years. The number of nodules produced per plant in a growth chamber decreased and was correlated to the number of bacteria surviving on the seeds. Changes in physiological properties were assessed using biochemical, physiological and microscopic methods. The cell total sugars content decreased with increased storage of the inoculants. High calculated ratios of suspended solid dry matter/carbon/nitrogen/proteins weight per c.f.u. strongly suggested the presence of dead or viable but non-culturable (VBNC) cells in the inoculants. This was confirmed in a study of bacterial respiratory activity, using p-iodonitrotetrazolium reduction. The time of colony appearance on plates increased in the old inoculants stored for a long time, especially on yeast-free culture medium. The heterogeneity in colony size also increased with storage length. Inoculants stored for more than 2 years could be differentiated from the others by using nalidixic acid against cellular division. Nucleic acid staining of cells showed that the percentage of membrane-compromised bacteria in all the inoculants increased with increased storage length, whatever the type of packaging used for the inoculants. These results demonstrated that the physiological activity of B. japonicum cells in commercial liquid inoculants changes after storage. To complete c.f.u. determination, three methods were proposed to assess the fitness of stored bradyrhizobia, but they remain to be checked for reliability on a variety of commercial inoculants.     

Transposition of IS1397 in the Family Enterobacteriaceae and First Characterization of ISKpn1, a New Insertion Sequence Associated with Klebsiella pneumoniae Palindromic Units

IS1397 and ISKpn1 are IS3 family members which are specifically inserted into the loop of palindromic units (PUs). IS1397 is shown to transpose into PUs with sequences close or identical to the Escherichia coli consensus, even in other enterobacteria (Salmonella enterica serovar Typhimurium, Klebsiella pneumoniae, and Klebsiella oxytoca). Moreover, we show that homologous intergenic regions containing PUs constitute IS1397 transpositional hot spots, despite bacterial interspersed mosaic element structures that differ among the three species. ISKpn1, described here for the first time, is specific for PUs from K. pneumoniae, in which we discovered it. A sequence comparison between the two insertion sequences allowed us to define a motif possibly accounting for their specificity.     

How predatory mites find plants with whitefly prey

We investigated the searching behaviour of two species of predatory mites, Typhlodromips swirskii (Athias-Henriot) and Euseius scutalis (Athias-Henriot), both known to feed on immature stages of the whitefly Bemisia tabaci Gennadius. When released in a greenhouse inside a circle of cucumber plants that were alternatingly clean or infested with immature whiteflies, the mites took several days to find plants. Both species were recaptured significantly more on plants with whiteflies. This suggests that the mites are able to discriminate between plants with and without whiteflies. The predators may either have been attracted to plants with whiteflies from a distance or arrested on plants with whiteflies. Typhlodromips swirskii that had previously fed on whitefly immatures on cucumber leaves were significantly attracted by volatiles from cucumber plants with whiteflies in a Y-tube olfactometer. This suggests that the mites use volatile cues to discriminate between infested and clean plants. However, this response waned rapidly; if predators, experienced as above, were starved for 3–4 h in absence of cucumber leaves, they no longer preferred volatiles of infested plants to clean plants. Furthermore, T. swirskii that had no experience with immature whiteflies on cucumber plants also did not prefer odours of infested plants to those of clean plants. Because the release experiment with this species in the greenhouse was done with inexperienced predators, this suggests that the aggregation of mites on plants with whiteflies was mainly caused by differential arrestment of mites on plants with prey and clean plants. For T. swirskii, this was in agreement with the finding that the fraction of predators on plants with prey increased with time to levels higher than 70%. A less clear trend was found for E. scutalis, for which the fraction of predators on plants with prey stabilized soon after release to levels from 54–70%. Hence, the predatory mites may find plants with prey by random searching, but they are subsequently arrested on these plants. An earlier study showed that 87% of all whiteflies released in a set-up as used here were recaptured within 1 day. Hence, the effectiveness with which predatory mites locate plants with whiteflies is low compared with that of their prey. We expect this to generate spatial patterns in the dynamics of predator and prey and this may have consequences for biological control of whiteflies with predatory mites.     

The endocannabinoid system controls key epileptogenic circuits in the hippocampus

Balanced control of neuronal activity is central in maintaining function and viability of neuronal circuits. The endocannabinoid system tightly controls neuronal excitability. Here, we show that endocannabinoids directly target hippocampal glutamatergic neurons to provide protection against acute epileptiform seizures in mice. Functional CB1 cannabinoid receptors are present on glutamatergic terminals of the hippocampal formation, colocalizing with vesicular glutamate transporter 1 (VGluT1). Conditional deletion of the CB1 gene either in cortical glutamatergic neurons or in forebrain GABAergic neurons, as well as virally induced deletion of the CB1 gene in the hippocampus, demonstrate that the presence of CB1 receptors in glutamatergic hippocampal neurons is both necessary and sufficient to provide substantial endogenous protection against kainic acid (KA)-induced seizures. The direct endocannabinoid-mediated control of hippocampal glutamatergic neurotransmission may constitute a promising therapeutic target for the treatment of disorders associated with excessive excitatory neuronal activity.     

Impact of the invasive ant Wasmannia auropunctata (Formicidae: Myrmicinae) on local ant diversity in southern Cameroon

The little fire ant, Wasmannia auropunctata Roger, is one of the world's most destructive invasive ants. It has been present in Cameroon for more than four decades, but its impact on local ant diversity is not known. We studied impact of W. auropunctata in three disturbed habitats located in rural and urban areas. We monitored ant diversity in both invaded and noninvaded zones in each area using a combination of three sampling methods: bait, pitfall traps and visual catch in quadrat. We collected 28 species in urban area and 64 in rural area. In invaded zone, W. auropunctata made up 97.72% and 99.96% of all ant fauna and ant species richness decreased to 7 and 2 in urban and rural area, respectively. In accordance with others findings in introduced environments, the presence of W. auropunctata has severely reduced abundance and richness of local ant species in both urban and rural environments in Cameroon. Measures should therefore be put in place to prevent its introduction in natural environment as forest reserves and natural parks.