Gentamicin and amikacin repress the growth of Plasmodium falciparum in culture, probably by inhibiting a parasite acid phospholipase

Human erythrocytes were loaded with either gentamicin or amikacin and subsequently infected with the human malarial parasite Plasmodium falciparum and grown in culture. Parasite invasion of erythrocytes was unaffected by the drugs, but subsequent development was retarded. The digestion of host cell cytosol in ring-stage parasites was inhibited by the drugs. A substantial acid, Ca2+-independent phospholipase activity could be monitored in parasite cytosol and was found to be inhibited by the drugs. These results imply that phospholipases are involved in the feeding mechanism of the parasite and that gentamicin and amikacin exert their inhibitory activity by affecting these enzymes.     

Translation efficiency in humans: tissue specificity,global optimization and differences between developmental stages

Various studies in unicellular and multicellular organisms have shown that codon bias plays a significant role in translation efficiency (TE) by co-adaptation to the tRNA pool. Yet, in humans and other mammals the role of codon bias is still an open question, with contradictory results from different studies. Here we address this question, performing a large-scale tissue-specific analysis of TE in humans, using the tRNA Adaptation Index (tAI) as a direct measure for TE. We find tAI to significantly correlate with expression levels both in tissue-specific and in global expression measures, testifying to the TE of human tissues. Interestingly, we find significantly higher correlations in adult tissues as opposed to fetal tissues, suggesting that the tRNA pool is more adjusted to the adult period. Optimization based analysis suggests that the tRNA pool—codon bias co-adaptation is globally (and not tissue-specific) driven. Additionally, we find that tAI correlates with several measures related to the protein functionally importance, including gene essentiality. Using inferred tissue-specific tRNA pools lead to similar results and shows that tissue-specific genes are more adapted to their tRNA pool than other genes and that related sets of functional gene groups are translated efficiently in each tissue. Similar results are obtained for other mammals. Taken together, these results demonstrate the role of codon bias in TE in humans, and pave the way for future studies of tissue-specific TE in multicellular organisms.     

Swabbing Often Fails to Detect Amphibian Chytridiomycosis under Conditions of Low Infection Load

The pathogenic chytrid fungus, Batrachochytrium dendrobatidis (denoted Bd), causes large-scale epizootics in naïve amphibian populations. Intervention strategies to rapidly respond to Bd incursions require sensitive and accurate diagnostic methods. Chytridiomycosis usually is assessed by quantitative polymerase chain reaction (qPCR) amplification of amphibian skin swabs. Results based on this method, however, sometimes yield inconsistent results on infection status and inaccurate scores of infection intensity. In Asia and other regions where amphibians typically bear low Bd loads, swab results are least reliable. We developed a Bd-sampling method that collects zoospores released by infected subjects into an aquatic medium. Bd DNA is extracted by filters and amplified by nested PCR. Using laboratory colonies and field populations of Bombina orientalis, we compare results with those obtained on the same subjects by qPCR of DNA extracted from swabs. Many subjects, despite being diagnosed as Bd-negative by conventional methods, released Bd zoospores into collection containers and thus must be considered infected. Infection loads determined from filtered water were at least 1000 times higher than those estimated from swabs. Subjects significantly varied in infection load, as they intermittently released zoospores, over a 5-day period. Thus, the method might be used to compare the infectivity of individuals and study the periodicity of zoospore release. Sampling methods based on water filtration can dramatically increase the capacity to accurately diagnose chytridiomycosis and contribute to a better understanding of the interactions between Bd and its hosts.     

Nucleotide sequences and properties of the sites involved in lysogenic insertion of the bacteriophage HP1c1 genome into the Haemophilus influenzae chromosome.

Bacteriophage HP1c1 lysogenizes its host Haemophilus influenzae Rd by inserting its genome into the bacterial chromosome. The DNA segments corresponding to the integration regions on the phage and host chromosomes and the two junctions formed between phage and host sequences on lysogenic insertion were isolated and propagated in Escherichia coli HB101 as hybrid plasmids by using pBR322 as the vector. The nucleotide sequences in the vicinity of the point of recombinational insertion were determined. Phage and host DNA shared an extensive, nearly identical, segment that was 183 base pairs long. This segment consisted of 93 identical residues and a 27-residue portion containing 6 mismatches, followed by 63 identical residues. Recombinational insertion occurred within the 63-residue identical segment and involved neither duplication nor deletion of any residues. Short inverted repeats consisting of clustered A-T base pairs were present within the two 27-residue segments. Two additional sites on the host chromosome showed significant hybridization to the phage-host homology region.     

A re-evaluation of the cytology of cat Pacinian corpuscles

Summary The ultrastructure of cat mesenteric Pacinian corpuscles in cross and longitudinal sections has been examined. The terminal ends of lamellar cells of the inner core have been identified in longitudinal sections through the proximal portion of the inner core. These terminal bulbous expansions contain characteristic concentric membranes of rough endoplasmic reticulum and in some cases masses of oval membranous inclusions. The central axon as seen in cross section is oval in profile, having X-(short) and Y-(long) axes, and each axonal face is characterized by specializations of the axolemma. At the X-axis, the inner lamellae of the inner core tightly abut a smooth axolemma, with no intervening connective tissue matrix, in a manner reminiscent of a neuroepithelium. The axolemma of the Y-axis has numerous axonal spines (microspikes) that project into the cleft in the inner core. The extent of the axolemma having axonal spines can only be appreciated in longitudinal sections. The clefts contain a specialized connective tissue with elastic and collagen fibrils. The connective tissue compartment of fibers and matrix separating individual inner core lamellae is unique, in that it contains extremely thin collagen fibrils measuring approximately 15 nm in diameter. The diameter of collagen fibrils increases as the cleft is approached. Here the fibrils resemble typical endoneural collagen.     

Atriopeptin II elevates cyclic GMP, activates cyclic GMP-dependent protein kinase and causes relaxation in rat thoracic aorta

Synthetic atriopeptin II, an atrial natriuretic factor with potent vasodilatory effects, was studied in isolated strips of rat thoracic aorta to determine its actions on contractility, cyclic nucleotide concentrations and endogenous activity of cyclic nucleotide-dependent protein kinases. Atriopeptin II was found to relax aortic strips precontracted with 0.3 microM norepinephrine whether or not the endothelial layer was present. Relaxation to atriopeptin II was closely correlated in a time- and concentration-dependent manner with increases in cyclic GMP concentrations and activation of cyclic GMP-dependent protein kinase (cyclic GMP-kinase). The threshold concentration for all three effects was 1 nM. Atriopeptin II (10 nM for 10 min) produced an 80% relaxation, an 8-fold increase in cyclic GMP concentrations and a 2-fold increase in cyclic GMP-kinase activity ratios. Atriopeptin II did not significantly alter cyclic AMP concentrations or cyclic AMP-dependent protein kinase activity. These data suggest that cyclic GMP and cyclic GMP-kinase may mediate vascular relaxation to a new class of vasoactive agents, the atrial natriuretic factors. Similar effects have been observed with the nitrovasodilator, sodium nitroprusside, and the endothelium-dependent vasodilator, acetylcholine. Therefore, a common biochemical mechanism of action that includes cyclic GMP accumulation and activation of cyclic GMP-kinase may be involved in vascular relaxation to nitrovasodilators, endothelium-dependent vasodilators and atrial natriuretic factors.     

Role and location of NAD malic enzyme in thermogenic tissues of Araceae

This work was done to discover how those nonphotosynthetic tissues of the Araceae that become thermogenic release, as CO2, carbon recently fixed by phosphoenolpyruvate carboxylase. Extracts of clubs of the spadix of Arum maculatum showed no activity for phosphoenolpyruvate carboxykinase and low activities of NADP malic enzyme. NAD malic enzyme activity in the above extracts and in those of thermogenic tissues of other Araceae was appreciable. Analysis of homogenates of clubs of Typhonium giraldii by differential centrifugation and sucrose gradients showed that NAD malic enzyme was confined to mitochondria. Centrifugation of mitochondria after freezing and thawing left all the NAD malic enzyme in the supernatant. NAD malic enzyme in isolated, intact mitochondria was completely latent, and was completely protected from exogenous trypsin. The responses of this latency and protection to different concentrations of Triton X-100 suggested that none of the NAD malic enzyme was accessible from either the outside or the intermembrane space of the mitochondria. Treatment of excised clubs of A. maculatum with 2-N-butylmalonate largely prevented the development of the rapid respiration responsible for thermogenesis, and severely inhibited dark fixation of 14CO2. The conclusion is that in mature clubs of the Araceae phosphoenolpyruvate is converted to malate in the cytosol by phosphoenolpyruvate carboxylase and NAD malate dehydrogenase, and that this malate then enters the mitochondrial matrix where it is converted to pyruvate by NAD malic enzyme.     

Effect of Storm Events on Benthic Nitrifying Activity

Storm events resulted in a marked reduction in the benthic nitrifying activity of a stream receiving geothermal inputs of ammonium. Subsequently, nitrifying activity demonstrated a logarithmic increase until a stable activity was reached 10 to 12 days after the storm event. The rate of increase of poststorm nitrifying activity was used to calculate the nitrifier growth rate in situ (0.0075 to 0.0116 h⁻¹) which was lower than the growth rates observed for laboratory cultures of nitrifying bacteria isolated from the sediments (0.0233 to 0.0990 h⁻¹).