Force‐ and length‐dependent catastrophe activities explain interphase microtubule organization in fission yeast

The cytoskeleton is essential for the maintenance of cell morphology in eukaryotes. In fission yeast, for example, polarized growth sites are organized by actin, whereas microtubules (MTs) acting upstream control where growth occurs. Growth is limited to the cell poles when MTs undergo catastrophes there and not elsewhere on the cortex. Here, we report that the modulation of MT dynamics by forces as observed in vitro can quantitatively explain the localization of MT catastrophes in Schizosaccharomyces pombe. However, we found that it is necessary to add length‐dependent catastrophe rates to make the model fully consistent with other previously measured traits of MTs. We explain the measured statistical distribution of MT–cortex contact times and re‐examine the curling behavior of MTs in unbranched straight tea1Δ cells. Importantly, the model demonstrates that MTs together with associated proteins such as depolymerizing kinesins are, in principle, sufficient to mark the cell poles.     

Assessing risks of Wolbachia DNA cross-specimen contamination following mass collection and ethanol storage

Wolbachia and other intracellular bacteria that manipulate reproduction are widespread and can have major consequences on the ecology and evolution of their hosts. Several studies have attempted to assess the host range of these bacteria based on polymerase chain reaction assays on material preserved and collected using a variety of methods. While collecting in the field, mass storage in ethanol before sorting specimens in the laboratory is by far the easiest technique, and an integral component of Malaise trapping. This implicitly relies on the assumption that mass ethanol storage does not produce cross-contamination of Wolbachia DNA among specimens. Here we test this assumption. The absence of cross contamination between known positive and negative samples stored within a vial indicate there is no reason to believe collective storage of specimens creates artefactual increases in the incidence of Wolbachia or other intracellular bacteria.     

Abundance and toxicity of Planktothrix rubescens in the pre-alpine Lake Ammersee,Germany

Regular occurrences of the cyanobacterium Planktothrix rubescens have been observed in several lakes that have undergone recent re-oligotrophication, e.g. Lake Ammersee. Planktothrix species are known to produce microcystins, potent phosphatase inhibitors that have been associated with morbidities and mortalities in humans and animals. The aim of this study was to characterise the temporal and spatial abundance and toxicity of P. rubescens in Lake Ammersee.P. rubescens cell densities and biovolumes were calculated via fluorescence image analyses. P. rubescens was present during the entire observation period from 1999 to 2004, albeit at different cell densities. Maximum biovolumes of 45 cm³ m^?2 were observed in May 2001. Filaments were regularly distributed over the entire water column during winter and stratified in distinct metalimnic layers during summer, reaching maximum cell densities of ≤15,000 (winter) and ≤77,000 cells ml^?1 (summer). The results demonstrate that P. rubescens abundance is strongly influenced by water transparency, i.e. illumination in the metalimnion. Moreover, the P. rubescens abundance appears to result from regular phosphate depletion in the epilimnion, possibly additionally benefiting from high nitrogen loads.Microcystin (MC) was detectable in 27 and 38 of 54 seston samples via HPLC and Adda-ELISA measurements, respectively. The main microcystin congeners in the seston samples were [Asp³]-MC-RR and [Asp³,Dhb⁷]-MC-RR. Microcystin concentrations correlated significantly with the respective phycoerythrin (PE)-concentrations. The variation in the MC/PE-ratios was low suggesting that the microcystin production of P. rubescens in Lake Ammersee is consistent and indicates that the appearance of P. rubescens coincides with measurable microcystin levels. Moreover, the observation of pronounced metalimnic oxygen depletions appears to be causally related to recurring high P. rubescens abundance.In conclusion the results suggest that aquatic organisms such as indigenous fish populations (e.g. coregonids) are regularly confronted with potentially adverse P. rubescens densities, which might provide a possible explanation for the often observed impaired health and growth retardation of coregonid populations in P. rubescens containing pre-alpine lakes.     

Biological activities and chemistry of saponins from Chenopodium quinoa Willd.

Chenopodium quinoa Willd. is a valuable food source which has gained importance in many countries of the world. The plant contains various bitter-tasting saponins which present an important antinutritional factor. Various triterpene saponins have been reported in C. quinoa including both monodesmosidic and bidesmosidic triterpene saponins of oleanolic acid, hederagenin, phytolaccagenic acid, and serjanic acid as the major aglycones and other aglycones as 3β-hydroxy-23-oxo-olean-12-en-28-oic acid, 3β-hydroxy-27-oxo-olean-12-en-28-oic acid, and 3β, 23α, 30β-trihydroxy-olean-12-en-28-oic acid. A tridesmosidic saponin of hederagenin has also been reported. Here we review the occurrence, analysis, chemical structures, and biological activity of triterpene saponins of C. quinoa. In particular, the mode of action of the mono- and bidesmosidic triterpene saponins and aglycones are discussed.     

A new class of small molecule RNA polymerase inhibitors with activity against rifampicin-resistant Staphylococcus aureus

The RNA polymerase holoenzyme is a proven target for antibacterial agents. A high-throughput screening program based on this enzyme from Staphylococcus aureus had previously identified a 2-ureidothiophene-3-carboxylate as a low micromolar inhibitor. An investigation of the relationships between the structures of this class of compounds and their inhibitory- and antibacterial activities is described here, leading to a set of potent RNA polymerase inhibitors with antibacterial activity. Characterization of this bioactivity, including studies of the mechanism of action, is provided, highlighting the power of the reverse chemical genetics approach in providing tools to inhibit the bacterial RNA polymerase.     

Characterization of ATP‐induced cell death in the GL261 mouse glioma

Gliomas have one of the worst prognosis among cancers. Their resistance to cell death induced by endogenous neurotoxic agents, such as extracellular ATP, seems to play an important role in their pathobiology since alterations in the degradation rate of extracellular ATP drastically affects glioma growth in rats. In the present work we characterized the mechanisms of cell death induced by extracellular ATP in a murine glioma cell line, GL261. ATP and BzATP, a P2X7 agonist, induced cell death at concentrations that are described to activate the P2X7 receptor in mouse. oATP, an antagonist of P2X7, blocked the ATP‐induced cell death. Agonists of purinergic receptors expressed in GL261 such as adenosine, ADP, UTP did not cause any cell death, even at mM concentrations. A sub‐population of cells more sensitive to ATP expressed more P2X7 when compared to a less sensitive subpopulation. Accordingly, RNA interference of the P2X7 receptor drastically reduced ATP‐induced cell death, suggesting that this receptor is necessary for this effect. The mechanism of ATP‐induced cell death is predominantly necrotic, since cells presented shrinkage accompanied by membrane permeabilization, but not apoptotic, since no phosphatidylserine externalization or caspase activity was observed. These data show the importance of P2X7 in ATP‐induced cell death and shed light on the importance of ATP‐induced cell death in glioma development. J. Cell. Biochem. 109: 983–991, 2010. © 2010 Wiley‐Liss, Inc.     

Survival of bacteria on metallic copper surfaces in a hospital trial

Basic chemistry of copper is responsible for its Janus-faced feature: on one hand, copper is an essential trace element required to interact efficiently with molecular oxygen. On the other hand, interaction with reactive oxygen species in undesired Fenton-like reactions leads to the production of hydroxyl radicals, which rapidly damage cellular macromolecules. Moreover, copper cations strongly bind to thiol compounds disturbing redox-homeostasis and may also remove cations of other transition metals from their native binding sites in enzymes. Nature has learned during evolution to deal with the dangerous yet important copper cations. Bacterial cells use different efflux systems to detoxify the metal from the cytoplasm or periplasm. Despite this ability, bacteria are rapidly killed on dry metallic copper surfaces. The mode of killing likely involves copper cations being released from the metallic copper and reactive oxygen species. With all this knowledge about the interaction of copper and its cations with cellular macromolecules in mind, experiments were moved to the next level, and the antimicrobial properties of copper-containing alloys in an “everyday” hospital setting were investigated. The alloys tested decreased the number of colony-forming units on metallic copper-containing surfaces by one third compared to control aluminum or plastic surfaces. Moreover, after disinfection, repopulation of the surfaces was delayed on copper alloys. This study bridges a gap between basic research concerning cellular copper homeostasis and application of this knowledge. It demonstrates that the use of copper-containing alloys may limit the spread of multiple drug-resistant bacteria in hospitals.