Use of Integrated Cell Culture-PCR To Evaluate the Effectiveness of Poliovirus Inactivation by Chlorine

Current standards, based on cell culture assay, indicate that poliovirus is inactivated by 0.5 mg of free chlorine per liter after 2 min; however, integrated cell culture-PCR detected viruses for up to 8 min of exposure to the same chlorine concentration, requiring 10 min for complete inactivation. Thus, the contact time for chlorine disinfection of poliovirus is up to five times greater than previously thought.     

Spatial pattern and variability in soil N and P availability under the influence of two dominant species in a pine forest

The presence of a legume in a nitrogen (N)-limited forest ecosystem may not only create ??islands of N fertility?? but also affect the phosphorus (P) availability. The main objective of this study was to compare the effect of a pine (Pinus canariensis) and a leguminous (Adenocarpus viscosus) species on the spatial pattern and variability of different labile organic-N (microbial biomass-N [MB-N] and dissolved organic-N [DON]), as well as inorganic-N (IN) and ?CP fractions (NH₄-N, NO₃-N, and PO₄-P), in a forest soil of the Canary Islands (Spain). Assuming some litter quantity and quality differences between these two species, we expected to find higher soil labile organic-N concentrations under isolated individuals of P. canariensis than under isolated individuals of A. viscosus. We also expected to find higher concentrations and spatial dependence (percentage of total variance explained by spatial autocorrelation) of NO₃-N beneath A. viscosus than beneath P. canariensis canopies, and higher spatial scaling of soil variables under the influence of P. canariensis canopies than under the presence of A. viscosus individuals. Moreover, we tested whether the soil variables measured under isolated individuals of both species showed a different spatial variability than the same soil variables measured under overlapping pine canopies inside a pine forest. To test these hypotheses, soil samples under isolated mature individuals of each species were collected in the winter and summer, whereas under a pine forest canopy, the sampling was performed only in the winter. The winter MB-N and DON concentrations were significantly higher beneath the pine individual, whereas the winter NO₃-N, NO₃-N-to-IN ratio, and PO₄-P were significantly higher under the leguminous individual; these differences were not observed in the summer samples. We found higher spatial ranges under the pine than under the legume canopy in the winter sampling, and the spatial dependence of NO₃-N was twice as high beneath the legumes as under the pines at both sampling dates. The soil spatial variability was higher (up to 17 times higher) under isolated individuals than inside the pine forest. The results of this study suggest that both the morphological and physiological characteristics of P. canariensis and A. viscosus, as well as the spatial pattern of P. canariensis, may influence the spatial pattern and variability of soil resources.     

A novel photosynthetic strategy for adaptation to low-iron aquatic environments

Iron (Fe) availability is a major limiting factor for primary production in aquatic environments. Cyanobacteria respond to Fe deficiency by derepressing the isiAB operon, which encodes the antenna protein IsiA and flavodoxin. At nanomolar Fe concentrations, a PSI-IsiA supercomplex forms, comprising a PSI trimer encircled by two complete IsiA rings. This PSI-IsiA supercomplex is the largest photosynthetic membrane protein complex yet isolated. This study presents a detailed characterization of this complex using transmission electron microscopy and ultrafast fluorescence spectroscopy. Excitation trapping and electron transfer are highly efficient, allowing cyanobacteria to avoid oxidative stress. This mechanism may be a major factor used by cyanobacteria to successfully adapt to modern low-Fe environments.     

Transport of L-Lactate, D-Lactate, and glycolate by the LldP and GlcA membrane carriers of Escherichia coli.

To examine the substrate specificity of the membrane transport carriers LldP (L-lactate permease) and GlcA (glycolate permease) of Escherichia coli, a mutant strain lacking their structural genes and blocked in the metabolism of the tested substrates was constructed and transformed with a plasmid bearing either the lldP or the glcA gene. Each transformant acquired the ability to accumulate L-lactate, D-lactate, and glycolate against a high concentration gradient. Substrate accumulation was inhibited by carbonyl cyanide m-chlorophenylhydrazone, a hydrophobic proton conductor that dissipates proton motive force. Competition of (14)C-L-lactate transport by nonradioactive L-lactate, D-lactate, and glycolate in LldP synthesizing cells and competition of (14)C-glycolate transport by the same three substrates in GlcA synthesizing cells showed that both carriers effectively transported all three substrates with a K(i) value ranging from 10 to 20 microM. D-Lactate does not appear to have a permease of its own. Utilization of the compound depends mainly on LldP.     

Similarity of mammalian body size across the taxonomic hierarchy and across space and time

Although it is commonly assumed that closely related animals are similar in body size, the degree of similarity has not been examined across the taxonomic hierarchy. Moreover, little is known about the variation or consistency of body size patterns across geographic space or evolutionary time. Here, we draw from a data set of terrestrial, nonvolant mammals to quantify and compare patterns across the body size spectrum, the taxonomic hierarchy, continental space, and evolutionary time. We employ a variety of statistical techniques including "sib-sib" regression, phylogenetic autocorrelation, and nested ANOVA. We find an extremely high resemblance (heritability) of size among congeneric species for mammals over approximately 18 g; the result is consistent across the size spectrum. However, there is no significant relationship among the body sizes of congeneric species for mammals under approximately 18 g. We suspect that life-history and ecological parameters are so tightly constrained by allometry at diminutive size that animals can only adapt to novel ecological conditions by modifying body size. The overall distributions of size for each continental fauna and for the most diverse orders are quantitatively similar for North America, South America, and Africa, despite virtually no overlap in species composition. Differences in ordinal composition appear to account for quantitative differences between continents. For most mammalian orders, body size is highly conserved, although there is extensive overlap at all levels of the taxonomic hierarchy. The body size distribution for terrestrial mammals apparently was established early in the Tertiary, and it has remained remarkably constant over the past 50 Ma and across the major continents. Lineages have diversified in size to exploit environmental opportunities but only within limits set by allometric, ecological, and evolutionary constraints.     

Safety signals from avoidance learning but not from yoked classical conditioning training pass both summation and retardation tests for inhibition

In one experiment half of the animals were trained to avoid a signaled footshock by jumping (30 or 160 trials), whereas the rest of the animals received the same events as yoked. For all of them the termination of the warning signal and of the shock was followed by a safety signal. Several tests were conducted to assess the ability of the stimuli to suppress licking by measuring the latency in completing 25 consecutive licks in the presence of the stimuli. Fear of the warning signal and inhibitory properties of the safety signal (summation and retardation tests) were measured. The results showed that there were no differences in fear to the warning signal, and that the safety signal behaves as a conditioned inhibitor only for animals trained with a long avoidance procedure, but not in the yoked (classical conditioning) procedure. These results highlight the role played by the avoidance response and its consequences in avoidance learning.