Organization and nucleotide sequence of the Streptococcus mutans galactose operon

The galactose operon encoding a repressor and genes for the Leloir pathway for galactose metabolism (galactokinase, galactose-1-phosphate-uridyl transferase and UDP glucose-4-epimerase) was located adjacent to the multiple sugar metabolism (msm) operon on the chromosome of Streptococcus mutans Ingbritt (serotype c) and the complete nucleotide sequence of this 5-kilobase region was determined. The Leloir pathway was induced by the presence of galactose in the growth medium or following the release of intracellular galactose after uptake and cleavage of -galactosides by the multiple sugar metabolism system. Analysis of the mechanism of galactose transport confirmed the absence of a galactose-specific phosphotransferase system and suggested the presence of an inducible galactose permease. Evidence is presented that galactose transport is independent of the proton motive force and may be ATP-dependent.     

Growth and foraging consequences of facultative paedomorphosis in the tiger salamander,Ambystoma tigrinum nebulosum

Summary Facultative paedomorphosis in salamanders occurs when larvae respond to varying environmental conditions by either metamorphosing into terrestrial metamorphic adults or retaining their larval morphology to become sexually mature paedomorphic adults. Several hypotheses have been proposed for the evolutionary maintenance of this environmentally induced dimorphism, but few data are available to assess them adequately. We studied a montane population of the tiger salamander,Ambystoma tigrinum nebulosum, and measured the adult growth rate and body condition across three growing seasons to assess the relative costs and benefits of each morph. Metamorphic adults grew more than paedomorphic adults in terms of snout—vent length across years and in weight within years. Dietary analyses and foraging experiments revealed some of the proximate factors that may underlie these differential growth patterns. Across all prey, metamorphs had significantly higher biomass and calories per stomach sample than paedomorphs. Metamorphic diets primarily consisted of the fairy shrimpBranchinecta coloradensis, whereas paedomorphic diets contained a variety of benthic and terrestrial invertebrates. Foraging experiments revealed that both morphs are more successful at capturing fairy shrimp relative to other prey types and both show high electivity toward this prey. However, fairy shrimp occurred only in non-permanent ponds and thus are inaccessible to paedomorphs, which can survive only in permanent ponds. Paedomorphs also experience higher levels of intraspecific competition with large larvae in permanent ponds than metamorphs do in non-permanent ponds. Thus, metamorphs obtain a growth advantage over paedomorphs by foraging in non-permanent ponds that contain fairy shrimp and have reduced intraspecific competition. These results suggest that paedomorphs should have decreased fitness relative to metamorphs, primarily because metamorphs can move into the best habitats for growth. The net fitness effect of morph-specific differences in dispersal depend on whether there are trade-offs with other life history traits. Nonetheless, because the relative benefit of metamorph dispersal will change with environmental conditions in permanent ponds and the surrounding habitat, the relative fitness payoff to each morph should track changes in the environment. Thus, facultative paedomorphosis may be maintained in part by variable, environmentally-specific fitness payoffs to each morph.     

Perceptual constraints on optimal foraging: The effects of variation among foragers

Summary We present a simple model of habitat selection in which individuals differ in their ability to discriminate between resource sites' profitabilities. The model investigates the effects of violating the ideal assumption of the well-known ideal free distribution (IFD). We show that (1) variability in perceptual limits within a population can significantly change the distribution of foraging animals even though the mean perceptual limit is the same, (2) the direction of this change depends on the proportion of the population that choose randomly between resource sites and (3) better perceivers are more likely to be found at individually more profitable sites, which, because of undermatching with respect to the IFD, are also the absolutely more profitable sites. We note that variability in perceptual limits almost always led to an undermatching of organisms to resources, thereby extending previous workers' results implying that the incorporation of any form of perceptual limits leads to undermatching with respect to the IFD.     

Inheritance of black sigatoka disease resistance in plantain-banana (Musa spp.) hybrids

Black sigatoka (Mycosphaerella fijiensis Morelet), an airborne fungal leaf-spot disease, is a major constraint to plantain and banana (Musa spp.) production world-wide. Gaining further knowledge of the genetics of host-plant resistance will enhance the development of resistant cultivars, which is considered to be the most appropriate means to achieve stable production. Genetic analysis was conducted on 101 euploid (2x, 3x and 4x) progenies, obtained from crossing two susceptible triploid plantain cultivars with the resistant wild diploid banana Calcutta 4. Segregating progenies, and a susceptible reference plantain cultivar, were evaluated over 2 consecutive years. Three distinct levels of host response to black sigatoka were defined as follows: susceptible (< 8 leaves without spots), less susceptible (8–10) and partially resistant (> 10). Segregation ratios for resistance at the 2x level fitted a genetic model having one major recessive resistance allele (bs ₁) and two independent alleles with additive effects (bsr ₂ and bsr ₃). A similar model explains the results at the 4x level assuming that the favourable resistance alleles have a dosage effect when four copies of them are present in their respective loci (bs _i ⁴ ). The proposed model was further validated by segregation data of S ₁ progenies. Mechanisms of black sigatoka resistance are discussed in relation to the genetic model.     

Competition between electron acceptors in photosynthesis: Regulation of the malate valve during CO2 fixation and nitrite reduction

For maximal rates of CO₂ assimilation in isolated intact spinach chloroplasts the generation of the adequate NADPH/ATP ratio is achieved either by cyclic electron flow around photosystem I or by linear electron transport to oxaloacetate, nitrite or oxygen (Mehler-reaction). The interrelationships between these poising mechanisms turn out to be strictly hierarchical. In the presence of antimycin A, an inhibitor of ferredoxin-dependent cyclic electron transport, the reduction of both, oxaloacetate and nitrite, but not that of oxygen restores CO₂ fixation. When oxaloacetate and nitrite are added at low concentrations simultaneously during steady-state CO₂ fixation, the reduction of nitrite is clearly preferred over the reduction of oxaloacetate, but CO₂ fixation is not influenced. Nitrite reduction is not decreased upon addition of oxaloacetate, but vice versa. This is due to the regulation of NADP-malate dehydrogenase activation by electron pressure via the ferredoxin/thioredoxin system on the one hand, and by the NADPH/(NADP+NADPH) ratio (anabolic reduction charge, ARC) on the other hand. Thus the closing of the malate valve prevents drainage of reducing equivalents from the chloroplast (1) when a low ARC indicates a high demand for NADPH in the stroma and (2) when nitrite reduction reduces the electron pressure at ferredoxin. The malate valve is opened when cyclic electron transport is inhibited by antimycin A. Under these conditions the rate of malate formation is higher than in the absence of the inhibitor even in the presence of oxaloacetate, thus indicating that the regulation of the malate valve functions at various redox states of the acceptor side of Photosystem I.Abbreviations ARC anabolic reduction charge (NADPH/(NADP+NADPH)) - Chl chlorophyll - DTT dithiothreitol; Fd-ferredoxin - NADP-MDH NADP-malate dehydrogenase - OAA oxaloacetate - PS photosystem - qN non-photochemical quenching - qP photochemical quenching - _E quantum efficiency of PS II Dedicated to Prof. Dr. Hans Walter Heldt on the occasion of his 60th birthday.     

Multiple mechanisms of membrane anchoring of Escherichia coli penicillin-binding proteins

Abstract: The major penicillin-binding proteins (PBPs) of Escherichia coli play vital roles in cell wall biosynthesis and are located in the inner membrane. The high M _r PBPs 1A, 1B, 2 and 3 are essential bifunctional transglycosylases/transpeptidases which are thought to be type II integral inner membrane proteins with their C-terminal enzymatic domains projecting into the periplasm. The low M _r PBP4 is a DD-carboxypeptidase/endopeptidase, whereas PBPs 5 and are DD-carboxypeptidases. All three low M _r , PBPs act in the modification of peptidoglycan to allow expansion of the sacculus and are thought to be periplasmic proteins attached with varying affinities to the inner membrane via C-terminal amphiphilic α-helices. It is possible that the PBPs and other inner membrane proteins form a peptidoglycan synthesizing complex to coordinate their activities.     

Active cell membrane mechanisms involved in the exclusion of RH 123 allow distinction between normal and tumoral cells

Human cell lines derived from three epithelial carcinomas (CaSki, HeLa, SiHa), one B lymphoma (BL60), one promyelocytic (HL60), one monocytic (U937) leukemia, one chronic myelogenous leukemia (sensitive K562S; multichemoresistant K562R) and normal human skin fibroblasts were compared for their capacity of staining with rhodamine 123 (Rh 123) and their kinetics of dye exclusion. Cells were exposed for 30 min to 10 g/ml of Rh 123 in culture medium; fluorescence intensity was measured by flow cytometry immediately or 1, 2, 3 and 4 h after staining. The highest fluorescence intensity was observed in carcinoma cell lines; there was no incorporation in multichemoresistant K562R cells. Exclusion of Rh 123 was evaluated from 0 to 4 h, both by flow cytometry and by fluorimetry. Fluorescence intensity measured by flow cytometry decreased slightly in carcinoma and leukemia cells and rapidly in fibroblasts. In all cell lines Rh 123 exclusion was inhibited by 40 mol/L verapamil and 5 mmol/L probenecid. Thus, incorporation and exclusion of Rh 123 allows distinction between normal and tumoral cells; moreover, inhibition of exclusion by verapamil and probenecid favors the involvement of active cell membrane mechanisms in the exclusion process.Abbreviations PBS phosphate-buffered saline - Rh 123 rhodamine 123     

正常菌群对常见致病菌拮抗作用的研究

生物拮抗作用是微生物种群关系研究的一个侧面,实验中我们使用从皮肤上分离的常住菌——痤疮丙酸杆菌(A14-1)和表皮葡萄球菌(F65)对常见致病菌如金黄色葡萄球菌(C189)、绿脓杆菌(C8514)和埃希氏大肠杆菌(C1356)的体外拮抗试验表明,它们具有明显的拮抗作用,拮抗作用一般从48小时开始,72小时明显。而皮肤常住菌间无拮抗作用,相反它们还有协同作用,这对于皮肤的自净以及维持皮肤的微生态平衡具有重要的作用。此外,实验中还进行了乳杆菌和双歧杆菌等正常菌群分离株与上述常见致病菌的体外拮抗试验,结果表明也     

Morpho-functional aspects of the hypothalanus-pituitary-gonadal axis of elasmobranch fishes

Synopsis The tetrapod hypothalamus-pars distalis axis contains a blood portal system. Contrarily, elasmobranchs appear to lack a direct vascular supply from the hypothalamus to the ventral lobe of the pituitary where gonadotropic activity resides. The hypothalamus contains GnRH immunoreactivity and GnRH causes an increase in plasma gonadal steroids, perhaps via ventral lobe stimulation. Therefore, the question arises as to how GnRH reaches the pituitary. We suggest that the general circulation route might be practicable. Indeed, in the plasma of the electric ray,Torpedo marmorata, a major early eluting form has been detected using high performance liquid chromatography coupled with region specific radioimmunoassay. The presence of GnRH in the blood may allow the molecule to reach the gonads and to act there by direct mechanisms. Intragonadal levels of steroids may have a paracrine and/or autocrine role in the regulation of steroidogenesis in the testis and in the development f specific germinal cell stages. Particularly, the zonated morphology of the testis supports the concept of a diverse environment for different spermatogenic stages. Finally, gonadal steroids may feed back to affect pituitary activity.     

重症肺炎患者病原菌分布、临床结局分析及血清尿素氮与肌酐比值、尿素氮与白蛋白比值联合检测的临床意义

摘要 目的：分析重症肺炎（SP）患者病原菌分布和临床结局并探讨血清尿素氮与肌酐比值（UCR）、尿素氮与白蛋白比值（UAR）联合检测的临床意义。方法：选取2019年8月～2022年8月三六三医院收治的107例SP患者,根据临床结局分为死亡组和存活组。分析SP患者病原菌分布情况。采用单因素和多因素Logistic回归分析SP患者临床结局的影响因素,采用受试者工作特征（ROC）曲线分析血清UCR、UAR水平对SP患者临床结局的评估价值。结果：107例SP患者痰液标本中培养出122株病原菌,其中革兰阴性菌75株（61.48%）,革兰阳性菌39株（31.97%）,真菌8株（6.56%）。107例SP患者院内死亡率为40.19%（43/107）。多因素Logistic回归分析显示,年龄增加、肺外并发症≥2个和UCR、UAR升高为SP患者临床结局不良的独立危险因素,氧合指数增加为其独立保护因素（P＜0.05）。ROC曲线分析显示,血清UCR、UAR联合评估SP患者临床结局的曲线下面积（AUC）大于各指标单独评估。结论：SP患者病原菌分布以革兰阴性菌为主,血清UCR、UAR升高为SP患者临床结局不良的独立危险因素,可能成为SP患者临床结局的辅助评估指标,且二者联合评估SP患者临床结局的价值较高。