The role of absC,a novel regulatory gene for secondary metabolism,in zinc‐dependent antibiotic production in Streptomyces coelicolor A3(2)

The availability of zinc was shown to have a marked influence on the biosynthesis of actinorhodin in Streptomyces coelicolor A3(2). Production of actinorhodin and undecylprodigiosin was abolished when a novel pleiotropic regulatory gene, absC, was deleted, but only when zinc concentrations were low. AbsC was shown to control expression of the gene cluster encoding production of coelibactin, an uncharacterized non‐ribosomally synthesized peptide with predicted siderophore‐like activity, and the observed defect in antibiotic production was found to result from elevated expression of this gene cluster. Promoter regions in the coelibactin cluster contain predicted binding motifs for the zinc‐responsive regulator Zur, and dual regulation of coelibactin expression by zur and absC was demonstrated using strains engineered to contain deletions in either or both of these genes. An AbsC binding site was identified in a divergent promoter region within the coelibactin biosynthetic gene cluster, adjacent to a putative Zur binding site. Repression of the coelibactin gene cluster by both AbsC and Zur appears to be required to maintain appropriate intracellular levels of zinc in S. coelicolor.     

Cancer-prone mice expressing the Ki-rasG12C gene show increased lung carcinogenesis after CT screening exposures

A >20-fold increase in X-ray computed tomography (CT) use during the last 30 years has caused considerable concern because of the potential carcinogenic risk from these CT exposures. Estimating the carcinogenic risk from high-energy, single high-dose exposures obtained from atomic bomb survivors and extrapolating these data to multiple low-energy, low-dose CT exposures using the Linear No-Threshold (LNT) model may not give an accurate assessment of actual cancer risk. Recently, the National Lung Cancer Screening Trial (NLST) reported that annual CT scans of current and former heavy smokers reduced lung cancer mortality by 20%, highlighting the need to better define the carcinogenic risk associated with these annual CT screening exposures. In this study, we used the bitransgenic CCSP-rtTA/Ki-ras mouse model that conditionally expresses the human mutant Ki-ras(G12C) gene in a doxycycline-inducible and lung-specific manner to measure the carcinogenic risk of exposure to multiple whole-body CT doses that approximate the annual NLST screening protocol. Irradiated mice expressing the Ki-ras(G12C) gene in their lungs had a significant (P = 0.01) 43% increase in the number of tumors/mouse (24.1 ± 1.9) compared to unirradiated mice (16.8 ± 1.3). Irradiated females had significantly (P < 0.005) more excess tumors than irradiated males. No tumor size difference or dose response was observed over the total dose range of 80-160 mGy for either sex. Irradiated bitransgenic mice that did not express the Ki-ras(G12C) gene had a low tumor incidence (≤ 0.1/mouse) that was not affected by exposure to CT radiation. These results suggest that (i) estimating the carcinogenic risk of multiple CT exposures from high-dose carcinogenesis data using the LNT model may be inappropriate for current and former smokers and (ii) any increased carcinogenic risk after exposure to fractionated low-dose CT-radiation may be restricted to only those individuals expressing cancer susceptibility genes in their tissues at the time of exposure.     

The respiratory properties of Biomphalaria glabrata exposed to Schistosoma mansoni infection,starvation, CO,and choices of different oxygen concentrations

The oxygen consumption rate (VO(2)) of Biomphalaria glabrata populations, using polarometric and manometric methods, when plotted against dried body mass as logarithmic co-ordinates, respectively, fell on a regression line with a slope between 0.933 and 1.02. The slope of the regression line for non-infected Schistosoma mansoni populations was found to be 1.04 with no differences in the VO(2) between infected and non-infected snails. The VO(2) of CO-treated snails was the same as for the control snails. The VO(2) of starved snails declined after 3 days and was half the original value after 10 days starvation at 27 degrees C. The P(50) value for snail haemolymph containing haemoglobin suspended in a Tris-HCl buffer was 5.57(+/-0.73)mmHg at a pH of 7.51 and 25 degrees C. For Sephadex-75 cleaned haemolymph the P(50) value was 1.72(+/-0.07)mmHg at 25 degrees C and pH 7.51. Snails exposed to oxygen fs and to choices of different oxygen concentrations in water did not exclusively prefer high (130mmHg), low (15mmHg), or normal (80mmHg) oxygen tensions. The oxygen consumption rate of 782 cercariae at 27 degrees C was measured as 0.0092 microl O(2)/h per single cercaria. The results, when compared with the data in the literature [Z. Vergl. Physiol. 46 (1963) 467;; S. A. J. Zool. 14 (1979) 202], indicate that the mantle cavity gas bubble plays an insignificant or no role at all when pulmonate snails are kept in water with high partial pressures of oxygen and at low temperatures.     

Flow-perfusion interferes with chondrogenic and hypertrophic matrix production by mesenchymal stem cells

Flow-perfusion is being promoted as a way to grow tissue-engineered cartilage in vitro. Yet, there is a concern that flow-perfusion may induce unwanted mechanical effects on chondrogenesis and terminal differentiation. Therefore, the aim of this study is to evaluate the effect of fluid flow on chondrogenesis and chondrocyte hypertrophy of MSCs in a well-established pellet culture model.     

Overwinter survival of carfentanil-immobilized male bison

A problem with studies that examine immobilization-related drug effects on large mammals is that no true control group exists because untreated (non-captured) animals in the same population have not been examined. We present data to show that overwinter survival in male bison (Bison bison) immobilized with carfentanil was the same as untreated bison. This unique experimental design allows us to conclude that the drug had no long-term effect on male bison overwinter survival.     

Trends in sightings and population structure of white sharks, <Emphasis Type="Italic">Carcharodon carcharias,</Emphasis> at Seal Island,False Bay,South Africa,and the emigration of subadult female sharks approaching maturity

A long-term sightings and photographic identification (photo-ID) database documented the inter-annual and monthly trends in white shark (Carcharodon carcharias) sightings, sex ratios and life-history stages at Seal Island, False Bay, South Africa, over the period 2004–2012. A total of 1105 sightings were recorded during 171 scientific surveys incorporating 577 h of observation (annual mean 64.10 h, range 23.71–178.69 h). The mean annual sighting rate was 1.87 (range 0.90–3.19) sharks per hour and sighting rates declined over the nine-year study period. It is unknown whether the decline resulted from an actual population decline, or was due to changes in shark distribution or environmental conditions, but it highlights the need for ongoing monitoring at this site. The overall sex ratio was 1.0: 1.0: 2.3 for male: female: unsexed sharks, respectively. Of the 1105 sightings, 39% (n = 433) were photo-ID’d, representing 303 individual sharks (112: 111: 80, male: female: unsexed) and 130 resightings. Of the 303 photo-ID’d sharks, 71% were sighted in a single year only, indicative of transient behaviour. Of the 29% of sharks that were resighted in more than one year, 65% were resighted in the following year, indicating site fidelity to Seal Island, whereas 35% skipped one or more years between encounters, indicative of a temporary absence. The majority (60%) of the photo-ID’d sharks were immature, 32% were subadult and only 8% were mature. No young-of-the-year sharks and few adults were recorded, indicating that Seal Island is not an adult aggregation site, nor a pupping or nursery area, but rather is best described as a seasonal feeding ground. Large females were rarely resighted again after they approached length-at-maturity (≥450 cm TL), whereas some adult males were recorded consistently across years. The emigration of subadult female sharks approaching maturity from Seal Island, combined with the small number of mature sharks of both sexes reported from any South African location, indicate that adult aggregation sites, and thus areas of reproductive importance, still remain unknown.     

Sucrose Represses the Developmentally Controlled Transient Activation of the Plastocyanin Gene in Arabidopsis thaliana Seedlings

The plastocyanin (PC) gene of Arabidopsis thaliana is activated independently of light during early seedling development. In etiolated seedlings, PC mRNA levels increase transiently and a maximum dark level is reached after 2 d of growth in darkness. In etiolated transgenic seedlings carrying a chimeric PC-promoter: luciferase fusion gene, luciferase activity is similarly increased after 2 d of growth. The transient increase in PC mRNA and luciferase activity levels can be repressed by sucrose. Nonmetabolizable sugars and polyethylene glycol do not have a major effect on PC gene expression. Also, light-grown seedlings show a similar transient and sucrose-sensitive increase in PC mRNA levels and luciferase activity, as in dark-grown seedlings, but here expression levels are 15- fold higher. These findings suggest the presence of a sucrose-sensitive, developmentally controlled expression mechanism that operates independently of light.     

Production of gamma-linolenic acid by Mucor circinelloides and Mucor rouxii with acetic acid as carbon substrate

Summary The production of gamma-linolenic acid (GLA) by Mucor circinelloides CBS 203.28 and M. rouxii CBS 416.77 in fed-batch cultures operated in pH-stat mode with acetic acid as carbon substrate and titrant compared favourably with the performance of M. circinelloides in batch culture on glucose. On acetic acid M. circinelloides accumulated up to 39.8 mg GLA/g biomass, with a crude oil content of 28% containing 91% neutral lipids. The GLA content of the neutral lipid fraction was 15.6%.