Structural and Functional Analysis of E. coli Cyclopropane Fatty Acid Synthase

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Probiotics in marine larviculture

Owing to the problem of antibiotic resistance and subsequent reluctance of using antibiotics, the use of probiotics in larviculture is becoming increasingly popular. During the early stages of development, manipulation of the larval digestive system seems possible through the addition of probiotics either through the culture water or via the livefood. Well-studied probiotics used in human medicine and terrestrial agriculture have proved to be successful in aquaculture and therefore reduce the need for extensive biosafety trials. The selection of probiotics requires various in vitro screening experiments, which assay for the production of antagonist compounds, their growth in and attachment to fish intestinal mucus, and the production of other beneficial compounds such as vitamins, fatty acids and digestive enzymes. Further information regarding probiont suitability can be obtained from its identification, interaction with livefood and host pathogenicity. Finally, pilot-scale in vivo tests need be performed, after which a production cost-benefit analysis to determine its economic viability needs to be undertaken.     

Use of the rotifer, Brachionus calyciflorus Pallas, in freshwater ornamental fish larviculture

The Brachionus calyciflorus used in this study were produced by batchculture using Chlorella spp. as feed. Larviculture experiments in indoor10-l and 200-l tanks revealed that, compared with egg yolk, the rotifersused as starter food significantly improved the growth and survival of DwarfGourami larvae (Day 2–12). These beneficial effects also extended tothe subsequent Artemia feeding phase (Day 13–32), suggesting that thequality of starter food is crucial to later development. At metamorphosis,the overall survival rate of larvae fed on rotifers in indoor tanks(65.1–74.5%) was about four times of that obtained in extensiveculture in open ponds (17.5%). In Discus, larvae are dependent on thebody slime of their parent as a nutrient during the first two weeks ofexogenous feeding. Our observation demonstrated that Brown Discus larvaecould be raised in the absence of the parent fish by using rotifers asstarter food followed by Artemia nauplii. Their growth and survival ratewere comparable to those on parental feeding. The artificial feeding wouldeliminate the risk of larvae being eaten by the parent fish and shorten thebrooding interval of the spawners, thereby leading to higher yield of fry.This feeding protocol is less tedious and more practical for use incommercial farming of Discus than the existing strategies of smuggling thebatch of larvae to foster parents or feeding the larvae with egg food. Theuse of rotifers would enable freshwater larviculture to improve larvalperformance, increase yield, and facilitate breeding of new fish specieswith small larvae.     

土壤酶学的研究进展

土壤酶在生态系统中是否作为一个组成成分,经典生态学没有明确的表述,但土壤酶在生态系统中具有重要的地位,它参与了包括土壤生物化学过程在内的自然界物质循环。介绍土壤酶的研究历史,土壤酶的检测技术、土壤酶的来源、土壤状况与土壤酶活性的关系、管理措施对土壤酶的影响等方面的研究进展,旨在推动土壤酶学的研究和利用。     

Effects of bacterial treatment at early stages of Atlantic cod (Gadus morhua L.) on larval survival and development

Aims: To assess the effects of bacterial treatment at the earliest stages of cod rearing on the microbial load, larval development and performance, testing three bacterial strains (Carnobacterium divergens V41, Arthrobacter sp. and Enterococcus sp.) in vivo that were previously shown to have inhibitory potential towards fish pathogens in vitro. Methods and Results: A bacterial mixture was added eight times to the rearing water from the prehatch to the mid‐larval stage (a 38‐day period). Microbiological analysis of ova, larvae and rearing water was performed regularly. Larval performance and development were evaluated by survival rate, hypersalinity tolerance and physiological measurements. Different larval survival rates were observed within and between treatments, and possibly explained by variations in larval microflora and established probionts. Larvae from one silo, which had been bathed in the bacterial suspension, showed the highest survival rate (42·1%), lowest Vibrio levels, and were significantly heavier (19·3%) and more stress tolerant than control larvae (P < 0·01). This coincided with the intestinal establishment of two of the tested bacteria. Conclusions: Arthrobacter and Enterococcus strains added regularly to the rearing water from the postfertilized egg stage can become established in larval gastrointestinal tract. The Enterococcus strain was associated with increased larval growth, performance and microflora control, indicating its probiotic nature. Significance and Impact of the Study: Regular application of autochthonous probionts may promote larval welfare, development and stress tolerance at early stages, hence increasing production yield in intensive cod larviculture.     

有机介质中酶催化活性和选择性的调控

有机溶剂中酶的结构与功能与在水中有很大的不同,通过调整控制策略可系统地改善酶针对目标反应的活性和选择性,重点阐述了溶剂对酶催化反应的活性和选择性的影响,介绍了酶催化选择性的热力学预测模型。,     

谷胱甘肽硫转移酶(GST)的固定化及酶学特性研究

对谷胱甘肽硫转移酶的固定化、游离酶和固定化酶的酶学特性进行了研究,通过试验,确定谷胱甘肽硫转移酶的最佳固定化条件为先用2％壳聚糖吸附酶,然后再加戊二醛交联,交联用戊二醛浓度为1．2％,交联时间6h;游离酶的最适温度为45—55℃,最适pH值为6．5-7．0：固定化酶的最适温度为45-50℃,最适pH值为7．0;游离酶和固定化酶的最适酶促反应时间为30min。     

Dietary ascorbic acid requirements during the hatchery production of turbot larvae

The effect of high ascorbic acid (AA) levels transferred through enriched live food was evaluated for turbot Scophthalmus maximus larvae in two consecutive feeding experiments. The same feeding strategy was applied to all treatments, except for the AA content of the live food which was manipulated through bioencapsulation with ascorbyl palmitate. This resulted finally in a low, medium and high-AA treatment. The AA incorporation levels in the turbot larvae (up to 1400 μg AA g DW⁻¹) were correlated with the AA content of the live food administered. However, feeding the high AA concentration resulted in the same values as for the medium treatment, indicating a saturation of the body AA reserves. Under standard culture conditions, no differences in growth nor overall survival could be detected among the different groups, illustrating that the dietary AA requirements of larval turbot are met by non-enriched live food containing already 500 μg AA g DW⁻¹. The larvae of the high-AA treatment, however, showed a better pigmentation rate (47 and 32% for experiments 1 and 2, respectively) compared to the other groups (35 and 25%, respectively). Evaluation of the physiological condition applying a salinity stress test revealed an improvement by feeding extra AA, significantly in the medium-AA treatment. Though not significantly different, cumulative mortalities after challenge with Vibrio anguillarum amounted to 50% for the control v. 40% for the fish fed medium and high-AA diets, respectively. Moreover, the onset of mortalities in this study was slower (not significantly) for the fish fed the extra AA.     

The Pyrimidine Nucleoside Phosphorylase of Mycoplasma hyorhinis and How It May Affect Nucleoside-Based Therapy

Mycoplasmas are opportunistic parasites and some species are suggested to preferentially colonize tumor tissue in cancer patients. We could demonstrate that the annotated thymidine phosphorylase (TP) gene in the genome of Mycoplasma hyorhinis encodes a pyrimidine nucleoside phosphorylase (PyNP_Hyor) that not only efficiently catalyzes thymidine but also uridine phosphorolysis. The kinetic characteristics of PyNP_Hyor-catalyzed nucleoside and nucleoside analogue (NA) phosphorolysis were determined. We demonstrated that the expression of such an enzyme in mycoplasma-infected cell cultures dramatically alters the activity of various anticancer/antiviral NAs such as 5-halogenated pyrimidine nucleosides, including 5-trifluorothymidine (TFT). Due to their close association with human cancers, the presence of mycoplasmas may markedly influence the therapeutic efficiency of nucleoside-based drugs.     

Activation of proteases in an anaerobic sulphidogenic bioreactor

Activities of proteases were stimulated by specific sulphur metabolites during the enhanced hydrolysis of complex polymeric organic carbon in an anaerobic sulphidogenic environment. While sulphate at 1000 mg l(-1) inhibited proteases by 50%, there was a 2.5-fold increase in activity of proteases by added sulphite and a 3.6-fold increase from added sulphide. Two hypothetical models are proposed. First the sulphur species, sulphite (HSO3-) and sulphide (HS-), liberated at different times during the sulphate reduction process, directly activate the proteases, which are associated with the organic particulate matter, leading to a subsequent enhancement of hydrolysis of polymeric material. Second, they indirectly activate the proteases by neutralising the cations on the floc surface disrupting the integrity of the organic particulate floc therebye releasing further entrapped enzymes from the organic particulate matter.     

Thiosubstrates of cholinesterases of different origin

Review of the own and literature data on investigation of substrate specificity of different cholinesterases using thiosubstrates is presented. Dependence of cholinesteratic hydrolysis parameters on various elements of their structure—the acyl part, alkyl “bridge” between ester atom and onium group, and the molecule ammonium grouping—is considered using 44 thioesters in total. A comparative enzymological analysis of the substrate specificity is performed with use of thiocholine esters of acetic, propionic, and butyric acids for 40 cholinesterase preparations of mammals, insects, mollusks, and plants.     

Microfabricated arrays of cylindrical wells facilitate single‐molecule enzymology of α‐chymotrypsin

Single‐molecule enzymology allows scientists to examine the distributions of kinetic rates among members of a population. We describe a simple method for the analysis of single‐molecule enzymatic kinetics and provide comparisons to ensemble‐averaged kinetics. To isolate our model enzyme, α‐chymotrypsin, into single molecules, we use an array of cylindrical poly(dimethylsiloxane) wells 2 μm in diameter and 1.35 μm in height. Inside the wells, a protease assay with a profluorescent substrate detects α‐chymotrypsin activity. We hold the concentration of α‐chymotrypsin at 0.39 nM in a given well with an enzyme‐to‐substrate ratio of 1:6,666 molecules. Fluorescence emitted by the substrate is proportional to enzyme activity and detectable by a charge‐coupled device. This method allows for the simultaneous real‐time characterization of hundreds of individual enzymes. We analyze single‐molecule kinetics by recording and observing their intensity trajectories over time. By testing our method with our current instruments, we confirm that our methodology is useful for the analysis of single enzymes for extracting static inhomogeneity. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009