Comparative effects of trichothecene mycotoxins on bovine platelet function: Acetyl T-2 toxin,a more potent inhibitor than T-2 toxin

The effects of the trichothecene mycotoxins (acetyl T-2 toxin, T-2 toxin, HT-2 toxin, palmityl T-2 toxin, diacetoxyscirpenol (DAS), deoxynivalenol (DON), and T-2 tetraol) on bovine platelet function were examined in homologous plasma stimulated with platelet activating factor (PAF). The mycotoxins inhibited platelet function with the following order of potency: acetyl T-2 toxin > palmityl T-2 toxin = DAS > HT-2 toxin = T-2 toxin. While T-2 tetraol was completely ineffective as an inhibitor, DON exhibited minimal inhibitory activity at concentrations above 10×10^?4M. The stability of the platelet aggregates formed was significantly reduced in all mycotoxin treated platelets compared to that of the untreated PAF controls. It is suggested that the increased sensitivity of PAF stimulated bovine platelets to the more lipophilic mycotoxins may be related to their more efficient partitioning into the platelet membrane compared to the more hydrophilic compounds.     

Active and passive cation transport and L antigen hertogeneity in low potassium sheep red cells

Several lines of experimental evidence are presented suggesting that the L antigens in low potassium (LK) sheep red cells are associated with separate Na(+)K(+) pump flux is distinct from the action of anti-L(l) on K(+) leak flux, implying that K(+) leak transport sites may not be converted into active pumps by the L antiserum. Treatment of LK red cells with trypsin completely abolished both the stimulation of K(+) pump flux and the enhancement of the rate of ouabain binding brought about by anti- L. That this effect is due to a total destruction of the L(p) determinant associated with the LK pump was evident from the complete failure of anti-L(p) to bind to trypsinized LK red cells. The L(p) antigen can be effectively protected against the trypsin attack by prior incubation with anti-L, indicating that the sites for antibody binding and trypsin action may be closely adjacent at the structural level. Trypsin treatment, however, did not interfere with anti-L(l) reducing ouabain insensitive K(+) leak influx, nor did it prevent binding of anti-L(ly), the hemolytically active L antibody which is probably identical with anti-L(l). The functional independence of the L(p) and L(l) sites was documented by the observation that anti-L(l) still reduced K(+) leak influx in LK cells with experimentally induced high potassium concentrations, at which K(+) pump flux is fully suppressed, whether or not anti-L(p) was binding to the L(p) antigen associated with the LK pump.     

Multiple effects of temperature,photoperiod and food quality on the performance of a pine sawfly

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Trade-offs and coexistence in microbial microcosms

Trade-offs among the abilities of organisms to respond to different environmental factors are often assumed to play a major role in the coexistence of species. There has been extensive theoretical study of the role of such trade-offs in ecological communities but it has proven difficult to study such trade-offs experimentally. Microorganisms are ideal model systems with which to experimentally study the causes and consequences of ecological trade-offs. In model communities of E. coli B and T-type bacteriophage, a trade-off in E. coli between resistance to bacteriophage and competitive ability is often observed. This trade-off can allow the coexistence of different ecological types of E. coli. The magnitude of this trade-off affects, in predictable ways, the structure, dynamics and response to environmental change of these communities. Genetic factors, environmental factors, and gene-by-environment interactions determine the magnitude of this trade-off. Environmental control of the magnitude of trade-offs represents one avenue by which environmental change can alter community properties such as invasability, stability and coexistence. This revised version was published online in August 2006 with corrections to the Cover Date.     

Industrial microbiology of solar salt production

Solar salterns can be modeled as giant outdoor chemostats, much like a series of dams on a slow-moving river. Microorganisms and their products play an essential, but sometimes uncharacterized, role in salt production in these ponds, from seawater salinity up through NaCl saturation. They may physically affect the evaporation process and their by-products may chemically modify or bind with dissolved ions. Many solar salt facilities engage microbiologists to establish monitoring programs for analyses of nutrients, standing crop and associated biological variables in the ponds. Other solar salt companies engage microbiologists only when there are “crises” in the ponds that interfere with salt production. Journal of Industrial Microbiology & Biotechnology (2002) 28, 42–47 DOI: 10.1038/sj/jim/7000173 Received 20 May 2001/ Accepted in revised form 13 June 2001     

The Molecular and Genetic Basis of Repeatable Coevolution between Escherichia coli and Bacteriophage T3 in a Laboratory Microcosm

The objective of this study was to determine the genomic changes that underlie coevolution between Escherichia coli B and bacteriophage T3 when grown together in a laboratory microcosm. We also sought to evaluate the repeatability of their evolution by studying replicate coevolution experiments inoculated with the same ancestral strains. We performed the coevolution experiments by growing Escherichia coli B and the lytic bacteriophage T3 in seven parallel continuous culture devices (chemostats) for 30 days. In each of the chemostats, we observed three rounds of coevolution. First, bacteria evolved resistance to infection by the ancestral phage. Then, a new phage type evolved that was capable of infecting the resistant bacteria as well as the sensitive bacterial ancestor. Finally, we observed second-order resistant bacteria evolve that were resistant to infection by both phage types. To identify the genetic changes underlying coevolution, we isolated first- and second-order resistant bacteria as well as a host-range mutant phage from each chemostat and sequenced their genomes. We found that first-order resistant bacteria consistently evolved resistance to phage via mutations in the gene, waaG, which codes for a glucosyltransferase required for assembly of the bacterial lipopolysaccharide (LPS). Phage also showed repeatable evolution, with each chemostat producing host-range mutant phage with mutations in the phage tail fiber gene T3p48 which binds to the bacterial LPS during adsorption. Two second-order resistant bacteria evolved via mutations in different genes involved in the phage interaction. Although a wide range of mutations occurred in the bacterial waaG gene, mutations in the phage tail fiber were restricted to a single codon, and several phage showed convergent evolution at the nucleotide level. These results are consistent with previous studies in other systems that have documented repeatable evolution in bacteria at the level of pathways or genes and repeatable evolution in viruses at the nucleotide level. Our data are also consistent with the expectation that adaptation via loss-of-function mutations is less constrained than adaptation via gain-of-function mutations.     

Rapid and unexpected effects of piscivore introduction on trophic position and diet of perch (Perca flavescens) in lakes recovering from acidification and metal contamination

1. Yellow perch (Perca flavescens) are often the only surviving fish species in acidified lakes. We studied four lakes along a gradient of recovery from acidification and that had different food web complexities. All had abundant yellow perch, two had low piscivore abundance, one had a well‐established piscivore population and one was manipulated by introducing piscivorous smallmouth bass (Micropterus dolomieu). We hypothesised that there would be strong effects on perch abundance, behaviour and diet induced by the presence of piscivores. 2. In the manipulated lake, the bass reduced yellow perch abundance by 75% over a 2‐year period. Concomitantly, perch use of the pelagic habitat fell from 48 to 40%. 3. In contrast to findings from less disturbed systems, yellow perch in the littoral zone of the manipulated lake did not strongly shift from zooplankton to benthic food sources after the arrival of piscivores. Diet analysis using stable carbon isotopes revealed a strong continued reliance on zooplankton in all lakes, independent of the degree of piscivory. The failure to switch to benthos in the refuge area of the littoral zone is most likely related to the depauperate benthos communities in these formerly acidified lakes. 4. Yellow perch in lakes recovering from acidification face a considerable ecological challenge as the necessary switch to benthic diet is hindered by a low abundance of benthos. The arrival of piscivores in these recovering lakes imposes further restrictions on perch access to food items. We infer that future recovery of perch populations (and higher trophic levels) will have to be preceded by the re‐establishment of diverse benthic macroinvertebrate communities in these lakes.     

Predation on Moose Calves by European Brown Bears

Abstract: In North America, brown bears (Ursus arctos) can be a significant predator on moose (Alces alces) calves. Our study in Sweden is the first in which brown bears are the only predator on moose calves. Bears and moose occurred at densities of about 30/1,000 km² and 920/1,000 km², respectively, and bears killed about 26% of the calves. Ninety-two percent of the predation took place when calves were <1 month old. Bear predation was probably additive to other natural mortality, which was about 10% in areas both with and without bears. Females that lost their calves in spring produced more calves the following year (1.54 calves/F) than females that kept their calves (1.11 calves/F), which reduced the net loss of calves due to predation to about 22%.