The differentiation of bacterial isolates encountered in fieldwork

A numerical value for each isolate is obtained by adding the appropriate value for each positive test given by each organism.

The advantages and disadvantages of the method compared with more conventional methods of bacterial identification are discussed and some modifications or improvements are suggested. This simplified approach is presented as being suitable for obtaining information about the diversity of bacterial types on student fieldwork.     

DNMTs are required for delayed genome instability caused by radiation

The ability of ionizing radiation to initiate genomic instability has been harnessed in the clinic where the localized delivery of controlled doses of radiation is used to induce cell death in tumor cells. Though very effective as a therapy, tumor relapse can occur in vivo and its appearance has been attributed to the radio-resistance of cells with stem cell-like features. The molecular mechanisms underlying these phenomena are unclear but there is evidence suggesting an inverse correlation between radiation-induced genomic instability and global hypomethylation. To further investigate the relationship between DNA hypomethylation, radiosensitivity and genomic stability in stem-like cells we have studied mouse embryonic stem cells containing differing levels of DNA methylation due to the presence or absence of DNA methyltransferases. Unexpectedly, we found that global levels of methylation do not determine radiosensitivity. In particular, radiation-induced delayed genomic instability was observed at the Hprt gene locus only in wild-type cells. Furthermore, absence of Dnmt1 resulted in a 10-fold increase in de novo Hprt mutation rate, which was unaltered by radiation. Our data indicate that functional DNMTs are required for radiation-induced genomic instability, and that individual DNMTs play distinct roles in genome stability. We propose that DNMTS may contribute to the acquirement of radio-resistance in stem-like cells.     

Effects of ionizing radiation on the growth and allyl isothiocyanate accumulation of Wasabia japonica in vitro and ex vitro

Mutations were induced in tissue-cultured wasabi (Wasabia japonica Matsumura) by treating in vitro-derived shoot tips with either γ-rays or X-rays at 0, 10, 20, 40 or 80 Gy. Doses of up to 40 Gy of either γ- or X-ray treatments resulted in a survival rate of more than 60% in culture after 3 mo. The use of γ- or X-rays at doses between 10 Gy and 40 Gy to induce mutation in W. japonica resulted in an alteration of the growth and allyl isothiocyanate (AITC) content of multiple shoots after 3 mo. in culture on Murashige and Skoog medium containing 5 μM N⁶-benzyladenine (BA). Putative mutants from the 40 Gy treatments of either γ- or X-rays exhibited a reduction in shoot weight, number, and height, whereas treatments of either γ-rays or X-rays at 10 Gy and 20 Gy doses showed no significant differences in shoot growth. All shoots treated with 80 Gy were either necrotic or irregenerable, while those treated with 40 Gy produced deformed leaves, from both types of ionizing radiation. Concentrations of AITC were measured by the use of gas chromatography-mass spectrometry (GC-MS). The accumulation of AITC was shown to decrease when doses increased in both γ- and X-ray treatments, compared with the controls. Positive responses were solely occurred at 18 mo. after transfer of in vitro rooted shoots to the shade house. The survival rate, rhizome weight and AITC content of plants derived from shoots treated with 20 Gy or 40 Gy of either γ-rays or X-rays were significantly greater than those of the controls.     

Is activation of the intra-S checkpoint in human fibroblasts an important factor in protection against UV-induced mutagenesis?

The ATR/CHK1-dependent intra-S checkpoint inhibits replicon initiation and replication fork progression in response to DNA damage caused by UV (UV) radiation. It has been proposed that this signaling cascade protects against UV-induced mutations by reducing the probability that damaged DNA will be replicated before it can be repaired. Normal human fibroblasts (NHF) were depleted of ATR or CHK1, or treated with the CHK1 kinase inhibitor TCS2312, and the UV-induced mutation frequency at the HPRT locus was measured. Despite clear evidence of S-phase checkpoint abrogation, neither ATR/CHK1 depletion nor CHK1 inhibition caused an increase in the UV-induced HPRT mutation frequency. These results question the premise that the UV-induced intra-S checkpoint plays a prominent role in protecting against UV-induced mutagenesis.     

Microwave effect on diffusion: a possible mechanism for non-thermal effect

Abstract

In this study, we assume that microwave radiation affects hydrogen bonding between dipolar water molecules and through that diffusion in water at constant temperature. The experimental study was performed on the setup of two identical reservoirs filled with pure water and 0.9% NaCl solution and connected by a thin tube. Alterations of NaCl concentration in the reservoir initially filled with pure water were measured using the resistance of the solution as an indicator. The applied 450?MHz continuous-wave microwave field had the maximal specific absorption rate of 0.4?W/kg on the connecting tube. The standard deviation of water temperature in the setup was 0.02?°C during an experiment. Our experimental data demonstrated that microwave exposure makes faster the process of diffusion in water. The time required for reduction of initial resistance of the solution by 10% was 1.7 times shorter with microwave. This result is consistent with the proposed mechanism of low-level microwave effect: microwave radiation, rotating dipolar water molecules, causes high-frequency alterations of hydrogen bonds between water molecules, thereby affects its viscosity and makes faster diffusion.     

Experimental optimisation of the X-ray energy in microbeam radiation therapy

Microbeam radiation therapy has demonstrated superior normal tissue sparing properties compared to broadbeam radiation fields. The ratio of the microbeam peak dose to the valley dose (PVDR), which is dependent on the X-ray energy/spectrum and geometry, should be maximised for an optimal therapeutic ratio. Simulation studies in the literature report the optimal energy for MRT based on the PVDR. However, most of these studies have considered different microbeam geometries to that at the Imaging and Medical Beamline (50 μm beam width with a spacing of 400 μm). We present the first fully experimental investigation of the energy dependence of PVDR and microbeam penumbra. Using monochromatic X-ray energies in the range 40–120 keV the PVDR was shown to increase with increasing energy up to 100 keV before plateauing. PVDRs measured for pink beams were consistently higher than those for monochromatic energies similar or equivalent to the average energy of the spectrum. The highest PVDR was found for a pink beam average energy of 124 keV. Conversely, the microbeam penumbra decreased with increasing energy before plateauing for energies above 90 keV. The effect of bone on the PVDR was investigated at energies 60, 95 and 120 keV. At depths greater than 20 mm beyond the bone/water interface there was almost no effect on the PVDR. In conclusion, the optimal energy range for MRT at IMBL is 90–120 keV, however when considering the IMBL flux at different energies, a spectrum with 95 keV weighted average energy was found to be the best compromise.     

Mutagenesis and mutation transfer induced by ultraviolet light in plasmid-cloned DNA

We describe here simple techniques for increasing the frequency of UV-induced mutations in a DNA fragment cloned in plasmid pBR322. Irradiation of both the host and the plasmid DNA before transformation is necessary to produce new mutations in the plasmid DNA, presumably because the UV-damaged pBR322 replicon cannot efficiently induce the error-prone repair pathway of Escherichia coli. In contrast, U V irradiation of the plasmid DNA alone before transformation primarily causes the transfer of preexisting mutations from the host chromosome to homologous DNA present in the plasmid. The only other kind of mutants obtained were large deletions of the plasmid DNA. Two chromosomal mutations from the host galK gene and one from the lacZ gene have been transferred to the plasmid by UV irradiation of the plasmid DNA alone. The technique can thus be of general use.     

RUS家族对植物生长发育的调控作用

叶绿体基因组编码许多参与光合作用和其他代谢过程的关键蛋白质,在叶绿体中合成的代谢物对于植物正常的生长发育至关重要。根对紫外线-B辐射敏感[Root-UVB (ultraviolet radiation B)-sensitive, RUS]蛋白属于叶绿体蛋白,由高度保守的DUF647结构域组成,在参与植物形态发生、物质运输和能量代谢等多种生命活动的调控中发挥作用。本文就近年来关于RUS家族在植物的胚胎发育、光形态建成、维生素B6稳态、生长素转运和花药发育等生长发育过程中的相关研究进行回顾和总结,为深入研究其在植物生长发育中的分子调控机制提供了参考。     

Melanin processing by keratinocytes: A non‐microbial type of host‐pathogen interaction?

The mechanisms that regulate skin pigmentation have been the subject of intense research in recent decades. In contrast with melanin biogenesis and transport within melanocytes, little is known about how melanin is transferred and processed within keratinocytes. Several models have been proposed for how melanin is transferred, with strong evidence supporting coupled exo/endocytosis. Recently, two reports suggest that upon internalization, melanin is stored within keratinocytes in an arrested compartment, allowing the pigment to persist for long periods. In this commentary, we identify a striking parallelism between melanin processing within keratinocytes and the host‐pathogen interaction with Plasmodium, opening new avenues to understand the complex molecular mechanisms that ensure skin pigmentation and photoprotection.      

Ecomorphological convergence in Eleutherodactylus frogs: a case of replicate radiations in the Caribbean

Replicate radiations, the repeated multiplication of species associated with ecological divergence, have attracted much attention and generated as much debate. Due to the few well‐studied cases, it remains unclear whether replicate radiations are an exceptional result of evolution or a relatively common example of the power of adaptation by natural selection. We examined the case of Eleutherodactylus frogs, which radiated in the Caribbean islands resulting in more than 160 species that occupy very diverse habitats. A time‐calibrated phylogeny revealed that these frogs independently diversified on all larger islands producing species that occupy a broad range of microhabitats in different islands. Using phylogenetic comparative methods, we found an association between morphological traits and particular microhabitats, and for most microhabitats detected significant morphological convergence. Our results indicate Caribbean Eleutherodactylus are a novel example of replicate radiations, and highlight the predictability of evolutionary processes, as similar ecological opportunities can lead to similar outcomes.