Escalating Plasmodium falciparum antifolate drug resistance mutations in Macha, rural Zambia

Background

Artemisinin and its derivatives have been used for falciparum malaria treatment in China since late 1970s. Monotherapy and uncontrolled use of artemisinin drugs were common practices for a long period of time. In vitro tests showed that the susceptibility of Plasmodium falciparum to artemisinins was declining in China. A concern was raised about the resistance to artemisinins of falciparum malaria in the country. It has been reported that in vitro artemisinin resistance was associated with the S769N mutation in the PfATPase6 gene. The main purpose of this study was to investigate whether that mutation has occurred in field isolates from China.

Methods

Plasmodium falciparum field isolates were collected in 2006–2007 from Hainan and Yunnan provinces, China. A nested PCR-sequencing assay was developed to analyse the genotype of the PfATPase6 S769N polymorphism in the P. falciparum field isolates.

Results

The genotyping results of six samples could not be obtained due to failure of PCR amplification, but no S769N mutation was detected in any of the 95 samples successfully analysed.

Conclusion

The results indicate that the S769N mutation in the PfATPase6 gene is not present in China, suggesting that artemisinin resistance has not yet developed, but the situation needs to be watched very attentively.     

Sequence length required for homologous recombination in Cryptococcus neoformans

Cryptococcosis is a major threat to immunocompromised individuals. Isolates of Cryptococcus neoformans var. grubii and var. neoformans are responsible for most of the infections in the United States and Europe. In depth analysis of the virulence phenotype of this organism requires the generation of specific gene disruptions. The minimum sequence requirements for efficient homologous recombination has not been determined in Cryptococcus. To investigate the flanking DNA length requirements for efficient homologous recombination in variety grubii, the rates of homologous recombination of constructs with different lengths of flanking sequence at two loci, CAP59 and CNLAC1, were examined. Five gene disruption constructs were prepared for each locus with symmetric lengths of sequence homologous to the target gene with approximately 50, 100, 200, 300 or 400bp flanking the selectable marker for hygromycin resistance. In addition, two asymmetric constructs with 50bp on one side and 400bp on the other side were generated for each locus. Overall, symmetric constructs with 300bp or more of flanking sequence on each side and the asymmetric constructs were efficiently targeted for gene disruption by homologous recombination in C. neoformans var. grubii. With one exception, the rate of recovery of homologous recombinants using the longer or asymmetric constructs as targeting vectors was greater than five percent of total transformants. Symmetrical constructs with 100bp or less of homologous flanking sequence did not efficiently generate targeted gene disruptions because the rate of homologous recombinants was less than or equal to 1%.     

Exotic herbivores and fire energy drive standing herbaceous biomass but do not alter compositional patterns in a semiarid savanna ecosystem

Questions

Fire regime alterations are pushing open ecosystems worldwide past tipping points where alternative steady states characterized by woody dominance prevail. This reduces the frequency and intensity of surface fires, further limiting their effectiveness for controlling cover of woody plants. In addition, grazing pressure (exotic or native grazers) can reinforce woody encroachment by potentially reducing fine-fuel loads. We investigated the effects of different fire energies on the herbaceous plant community, together with mammalian wildlife herbivory (exotic and native combined) exclusion, to inform best management practices.

Location

Texas semi-arid savanna, southern Great Plains, USA.

Methods

We conducted an experiment in which we manipulated fire intensity and herbivore access to herbaceous biomass in a split-plot design. We altered fire energy via fuel addition rather than applying fire under different environmental conditions to control for differences in standing biomass and composition attributable to differential plant physiological status and fire season.

Results

High-energy fire did not reduce herbaceous biomass or alter plant community composition, although it did increase among-plot variability in composition and forb biomass relative to low-energy fire and non-burned controls. Grazing pressure from native and non-native mammalian herbivores reduced above-ground herbaceous biomass regardless of fire treatments, but did not alter community composition.

Conclusions

Managers seeking to apply high-intensity prescribed fire to reduce woody encroachment will not negatively impact herbaceous plant productivity or alter community composition. However, they should be cognizant that repeated fires necessary for greatly reducing woody plants in heavily invaded areas might be difficult to accomplish due to fine-fuel reduction from wild herbivores. High fencing to restrict access by wildlife herbivores or culling might be necessary to build fuels sufficient to conduct high-intensity burns for woody-plant reduction.     

Are bryophyte communities different from higher‐plant communities? Abundance relations

The considerable differences in biology between bryophytes and higher plants have led to speculation that their community structure might be different. Ten bryophyte communities were sampled for species biomass composition, and for comparison ten higher-plant communities that were similar in physiognomy and in total community biomass. The rather insecure theory in the bryophyte literature was distilled into eight quantifiable predictions, which were tested. For seven, there was no sign of the predicted differences: i.e. no indication of the predicted low within-community heterogeneity, higher species richness, more variable species richness, lower rank consistency, a poor fit for the geometric model of RAD (relative abundance distribution), better fit for the broken-stick and general-lognormal RAD models with general-lognormal parameter γ deviating further from 1.0, or of a good fit for the Zipf-Mandelbrot RAD model. However, evenness was, on average, significantly (p=0.005) less in the bryophyte communities, using any of four evenness indices. Two possible features of bryophytes are suggested that might cause this: (a) a smaller module (i.e. shoot, leaf) size, allowing species to be present with a lower threshold biomass, and (b) less efficient competitive exclusion among bryophytes because of weaker competition and a predominance of mutualism, as suggested in the literature. However, the striking conclusion from the results is that in spite of all the biological differences between the two groups of organisms, their community organisation is remarkably similar.     

Biological invasions: Lessons for ecology

Anthropogenic introduction of species is homogenizing the earth's biota. Consequences of introductions are sometimes great, and are directly related to global climate change, biodiversity AND release of genetically engineered organisms. Progress in invasion studies hinges on the following research trends: realization that species' ranges are naturally dynamic; recognition that colonist species and target communities cannot be studied independently, but that species-community interactions determine invasion success; increasingly quantitative tests of how species and habitat characteristics relate to invasibility and impact; recognition from paleobiological, experimental and modeling studies that history, chance and determinism together shape community invasibility.     

The Synthesis and Activity of cis-and trans-2-(Aminomethyl) cyclopropanecarboxylic Acid as Conformationally Restricted Analogues of GABA

Abstract: The synthesis of cis -2-(aminomethyl) cyclopropanecarboxylic acid, a new analogue of GABA in a folded conformation, is described, as is also an improved preparation of trans -2-(aminomethyl) cyclopropanecarboxylic acid. When adminstered microelectrophoretically the trans isomer was more potent than GABA as a bicuculline-sensitive depressant of the firing of cat spinal neurons in vivo , whereas the cis-isomer was less potent than GABA and its effects appeared not to be sensitive to bicuculline methochloride. Trans -2-(aminomethyl) cyclopropanecarboxylic acid was a weak inhibitor of the sodium-dependent uptake of GABA by mini slices of rat cerebral cortex and a substrate for the GABA: 2-oxoglutarate aminotransferase activity in extracts of rat brain mitochondria. The cis isomer did not influence GABA uptake or aminotransferase activity and neither isomer reduced glutamate decar-boxylase activity in rat brain homogenates. Both cyclopropane isomers inhibited the sodium-independent binding of GABA to synaptic membranes from rat brain and their relative potencies together with those found for the stereochemically related unsaturated derivatives, cis -and trans -4-aminocrotonic acid, were broadly consistent with the activity observed for these compounds in vivo on cat spinal neurons. These studies reinforce the evidence that extended rather than folded conformations of GABA are active at most GABA recognition sites within the mammalian central nervous system.     

Sex and outcrossing in a sessile freshwater invertebrate

SUMMARY 1. The freshwater bryozoan Cristatella mucedo , in common with other sessile, benthic freshwater taxa, has an unusual life history: sex occurs during a relatively brief period near the start of the growing season, and overwintering occurs in the form of asexually produced dormant propagules (statoblasts). Consistent observed heterozygosity (Ho) deficits in C. mucedo populations have previously suggested that inbreeding is common, although a possible contribution of a Wahlund effect to low Ho could not be discounted.
2. We have used microsatellite data in the first study based on codominant markers to genetically characterise maternal colonies and larval offspring of C. mucedo . The 'population' represented by the larvae was in Hardy–Weinberg equilibrium, which has previously been found in only one of 39 populations of C. mucedo . At least 64% of larvae were the products of outcrossing. We suggest that the unusual early timing of sex may be a strategy to maximise rates of outcrossing within populations of sessile freshwater invertebrates.     

Rooster spermatozoan motility,forward progression,and fertility after storage at 25, 5, or −196 °C in various extenders

Rooster spermatozoa were stored at 25, 5, or ?196 °C in either TC199, a pyruvate-lactate mouse ova culture medium, or as undiluted semen. There was a linear decrease in percent of motile sperm during storage at 25 or 5 °C in all cases, and a curvilinear decrease with increasing storage times at ?196 °C. Percent of motile sperm present after increasing storage time suggested pyruvate-lactate is a better extender than TC199 at the three storage temperatures studied. Pullets inseminated with 1 × 10⁸ motile sperm using fresh sperm diluted in TC199 or pyruvate-lactate, or stored 24 hr at 5 or ?196 °C produced 68.7, 74.1, 20.6, and 10.8% fertile eggs, respectively. The differences in fertility between controls or between samples stored at 5 and ?196 °C were not significant. However, fertility from sperm stored at 5 and ?196 °C was significantly lower (p < .05) than both control groups. Thus, it can be concluded that TC199 or pyruvate-lactate may be used to dilute fresh rooster semen collections prior to insemination. In contrast, fertility of rooster sperm is not satisfactorily maintained after 5 or ?196 °C storage for 24 hr in a pyruvate-lactate extender.     

Mutagenic activity of propylene oxide in bacterial and mammalian systems.

Propylene oxide is used extensively in the chemical and food manufacturing industries, but relatively little is known of its ability to interact with genetic material. Studies were undertaken to investigate its ability to induce gene mutations and primary DNA damage in bacteria and chromosomal damage in mammalian cells. The induction of base-substitution mutations was demonstrated in spot tests with strains of Salmonella typhimurium and Escherichia coli at 700 micrograms/plate of propylene oxide; inclusion of a preparation of rat-liver microsomes and cofactors (S9 mix) was without significant effect on this response. A linear dose--response relationship was recorded in plate tests with S. typhimurium strains TA100 and TA1535 over the range 100--750 micrograms/plate. After addition to dividing lymphocytes in cultures established from human peripheral blood, propylene oxide caused dose-related chromosomal damage, detected at 1.85 and 9.25 micrograms/ml. Oral administration of propylene oxide at 2 x 100, 2 x 250 or 2 x 500 mg/kg to male mice produced no detectable increases in the incidence of micronucleated, polychromatic erythrocytes in bone marrow. A male mouse dominant lethal test employing oral doses of 50 or 250 mg/kg/day for 14 days gave no evidence of mutagenic action on sperm. Intraperitoneal injections of propylene oxide at 2 x 300 mg/kg induced increased numbers of micronucleated erythrocytes in mice, but lower doses given by this route had no such effect. Possible reasons for the contrasting findings in vitro and in vivo are discussed.