The effect of cooling rate, freeze-drying suspending fluid and culture age on the preservation of Campylobacter pylori

The effects of freezing rate, suspending fluid and age of culture on the ability of four strains of Campylobacter pylori to survive and recover from freeze-drying were examined. Freeze-drying by standard procedures generally resulted in an overall loss in viability of between 3 and 7 log units. The exact cause of poor recovery by C. pylori was not established but strain differences were detected, with NCTC 11637 (type strain) surviving better than NCTC 11638 and NCTC 11639. Recovery of the poorest growing strain (NE 26695) was notably more erratic. The largest loss in viability occurred at the primary drying stage. Losses resulting from freezing and secondary drying were less marked and the rate of freezing had only a marginal effect on recovery. Nineteen different freeze-drying suspending fluids were investigated. Overall the best recovery results were obtained with 5% inositol-broth (or horse serum) plus 25% glucose, at pH 7.0, in which loss of viability was typically about 4 log units. Other factors, such as age of culture and number of viable bacteria in the before-dry suspension, did not have a significant effect on survival. We conclude from these results that C. pylori can survive freeze-drying, albeit in small numbers, but the degree of recovery is apparently largely strain dependent.     

中国皿蛛科蜘蛛一新属和一新种记述(蛛形纲:蜘蛛目)

本文记述采自新疆的皿蛛科蜘蛛一新届——颚齿蛛属Maxillodens gen.nov.及其一新种——鞭状颚齿蛛M.flageuatus sp.nov。     

Parallel phenotypic evolution in a wolf spider radiation on Galápagos

Within island archipelagos, repeated ecological settings may lead to radiations wherein similar niches are recurrently occupied. Although it has been shown that species with common habitat requirements share particular traits, it remains relatively unexplored to what extent this may lead to the repeated evolution of almost identical phenotypes (phenocopies) and how this correlates with traits subjected to sexual selection. Exploring divergence patterns of ecological and sexual relevant traits within spiders seem promising to enhance our understanding of the relative role of natural and sexual selection. Here, we conduct a detailed morphological analysis on a large set of genital and non‐genital traits (morphometrics, colour pattern) within a radiation of the wolf spider genus Hogna Simon, 1885 on Galápagos and interpret these data, taking into account their known phylogenetic relationship. Our results show that recurrent environmental gradients have led to the parallel evolution of almost identical phenotypes, which not only proves that natural selection has driven morphological divergence, but also suggests that a similar genetic or developmental basis most likely underlies this divergence. Among‐species variation in genital traits in contrast rather reflects the phylogenetic relationships on Santa Cruz and San Cristóbal. The combination of these data indicate that speciation in this system is driven by the combined effect of ecological mechanisms and allopatric divergence in sexual traits. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 123–136.     

Temporal variation in the genetic structure of host-associated populations of the small ermine moth Yponomeuta padellus (Lepidoptera, Yponomeutidae)

Temporal changes in allele frequencies were studied in host-associated populations of the small ermine moth Yponomeuta padellus. At one site, populations from three host plants (Sorbus aucuparia, Amelanchier larnarckii , and Crataegus spp.) were sampled annually during a four-year-period and analysed with 20 polymorphic allozyme markers. At two other sites, allele frequencies at 5- 6 enzyme loci of Y. padellus populations from two different host plants were also tested for consistency over a 13-year-pcriod. Significant allele frequency changes occurred in the short-term analysis, whereas allele frequencies remained relatively stable through time in the long-term analyses. Furthermore, allele frequencies of Y. padellus populations from Crataegus spp. were relatively stable compared to the other host populations. The role of the agents responsible for the observed patterns is discussed.     

A two-step purification procedure for sheep liver 6-phosphogluconate dehydrogenase

A two-step procedure for the purification of 6-phosphogluconate dehydrogenase (EC 1.1.1.44; 6-PGDH) from sheep liver is described. The enzyme is directly bound to cellulose phosphate by batch extraction and eluted with a linear salt gradient. Purification is completed by affinity chromatography using NADP(+)-agarose. The result is 6-PGDH of high purity, greatly increased yield, and the highest specific activity yet achieved, with a significant reduction in the purification time.     

Hydraulic failure and tree dieback are associated with high wood density in a temperate forest under extreme drought

Catastrophic hydraulic failure will likely be an important mechanism contributing to large‐scale tree dieback caused by increased frequency and intensity of droughts under global climate change. To compare the susceptibility of 22 temperate deciduous tree and shrub species to hydraulic failure during a record drought in the southeastern USA, we quantified leaf desiccation, native embolism, wood density, stomatal conductance and predawn and midday leaf water potential at four sites with varying drought intensities. At the two driest sites, there was widespread leaf wilting and desiccation, and most species exhibited predawn leaf water potentials of ≤3 MPa and >60% loss of xylem conductivity in branches. Although species with high wood density were more resistant to cavitation, they had higher levels of native embolism and greater canopy dieback than species with low wood density. This unexpected result can be explained by the failure of species with dense wood to avert a decline in water potential to dangerous levels during the drought. Leaf water potential was negatively correlated with wood density, and the relationship was strongest under conditions of severe water deficit. Species with low wood density avoided catastrophic embolism by relying on an avoidance strategy that involves partial drought deciduousness, higher sensitivity of stomata to leaf water potential and perhaps greater rooting depth. These species therefore maintained water potential at levels that ensured a greater margin of safety against embolism. These differences among species may mediate rapid shifts in species composition of temperate forests if droughts intensify due to climate change.     

微重力对石刁柏根尖组织和细胞中钙水平及分布的影响

用焦锑酸钾沉淀法进行了组织和细胞中游离钙的化学定位。用光学显微镜和透射电镜观察石刁柏幼苗在太空飞行后Ｃａ２＋沉淀颗粒在根尖组织和细胞内的分布。结果表明,太空飞行１５天后,Ｃａ２＋在各组织内的分布情况与地面对照无明显差异,但Ｃａ２＋的含量明显低于对照。Ｃａ２＋在细胞内不同区域的分布在飞行和对照样品中差异十分明显,对照细胞中Ｃａ２＋集中在液泡内,其它细胞器中很少见到。飞行幼苗的根尖细胞,液泡中Ｃａ２＋很少,并向液泡膜集结,液泡膜内侧和细胞质中的Ｃａ２＋明显增多。细胞壁中的Ｃａ２＋较对照有明显增加,高尔基体中也有少量钙存在。本文着重讨论了飞行幼苗根尖中Ｃａ２＋在细胞内重新分布的可能作用。     

Relative accuracy of spatial predictive models for lynx Lynx canadensis derived using logistic regression-AIC,multiple criteria evaluation and Bayesian approaches

We compared probability surfaces derived using one set of environmental variables in three Geographic Information Systems (GIS) -based approaches: logistic regression and Akaike's Information Criterion (AIC),Multiple Criteria Evaluation (MCE),and Bayesian Analysis (specifically Dempster-Shafer theory). We used lynx Lynx canadensis as our focal species,and developed our environment relationship model using track data collected in Banff National Park,Alberta,Canada,during winters from 1997 to 2000. The accuracy of the three spatial models were compared using a contingency table method. We determined the percentage of cases in which both presence and absence points were correctly classified (overall accuracy),the failure to predict a species where it occurred (omission error) and the prediction of presence where there was absence (commission error). Our overall accuracy showed the logistic regression approach was the most accurate (74.51% ). The multiple criteria evaluation was intermediate (39.22%),while the Dempster-Shafer (D-S) theory model was the poorest (29.90%). However,omission and commission error tell us a different story: logistic regression had the lowest commission error,while D-S theory produced the lowest omission error. Our results provide evidence that habitat modellers should evaluate all three error measures when ascribing confidence in their model. We suggest that for our study area at least,the logistic regression model is optimal. However,where sample size is small or the species is very rare,it may also be useful to explore and/or use a more ecologically cautious modelling approach (e.g. Dempster-Shafer) that would over-predict,protect more sites,and thereby minimize the risk of missing critical habitat in conservation plans.