Early Crop Root Destruction for Management of Tobacco Cyst Nematodes

Prompt tillage after crop harvest was investigated as a cultural control for the tobacco cyst nematode, Globodera tabacum tabacum, on stalk-cut broadleaf cigar wrapper tobacco. Stalk stumps and roots remaining after harvest were destroyed by tilling immediately or from 2 to 6 wk after harvest in field experiments over 4 yr. Cyst nematode Pf/Pi ratios ranged from 0.65 to 1.62 when plants were tilled immediately after harvest and 1.13 to 5.88 when tillage was delayed. Nematode population development was monitored by inoculating plants in pots placed in fields with J2 in eggs and sampling over time (8 to 18 wk). Three generations per year were observed, and G. t. tabacum generation time was as short as 6 wk for each generation. Destroying stalks and root systems remaining after harvesting stalk-cut broadleaf cigar wrapper tobacco removes the host to preclude development of nematodes at the end of the second and entire third generation. Early tillage resulted in consistently lower tobacco cyst nematode populations than allowing viable roots to remain in fields for an additional 8 to 18 wk. This management tactic reduces the need for nematicide application to slow nematode population increases over time and can reduce losses due to infection by G. t. tabacum.     

生境破坏的空间结构对集合种群续存的影响

生境破坏及其影响是生态学亟待解决的问题之一,目前的研究主要集中在破坏数量,即遭破坏生境的比例,对物种续存的影响方面;其中最主要的结论是Levins原理和适合生境斑块最小数量(MASH),而关于生境破坏的空间结构的研究却比较稀少,在本文中,我们首先将偶对近似引入到集合种群的研究当中,并替代原有的均匀场假设.然后我们对生境破坏导致的集合种群大小、空间结构以及分布等做了全面讨论.结果显示:随破坏比例的增加,集合种群大小将下降并且其分布将远离破坏生境.进一步聚集式分布结构将瓦解.随着破坏规则化的下降,集合种群将萎缩并使其聚集结构崩溃,在破坏生境周围集合种群起初将增加然后迅速消失.根据这些结果,我们可以对边界效应进行分析:不能用破坏比例描述生境破坏的程度和影响,而只能用破坏区域边界的长短来描述.根据边界效应,我们可以得出在一连通生境上物种保护的条件是生境破坏后剩余的适合生境比例应该大于破坏前原始生境的一半.居住在斑块环境中的物种比连续生境中生存的物种可以更好地抵抗生境破坏带来的影响.     

Evidence of autumn reproduction in female European hares (Lepus europaeus) from southern Europe

Information on reproductive biology of the European hare (Lepus europaeus) in different environmental and landscape conditions comprises part of fundamental knowledge regarding species’ adaptive responses as well as many aspects of its biology. Most of the studies conducted on European hare reproduction are confined to midlatitude and northern populations, whereas no data exist on the indigenous southern populations. Here, we present information on reproductive characteristics of European hares inhabiting Mediterranean ecosystems on the island of Crete, Greece for two successive hunting seasons. Although the annual reproductive cycle of the species is well known, with an autumn sexual inactivity, the duration of this period is subjected to fluctuations in different years and for different areas. According to our data, hare populations of Crete present an autumn–early winter reproductive activity with high proportions of pregnant females observed in all the months of the study. Furthermore, the estimated mean litter size (1.54 SE ± 0.07) while signed to the lowest values ever observed for European hares is similar to values obtained in continuous breeding species of the same genus, Lepus granatensis, Lepus corsicanus, Lepus (capensis) mediterraneus, and Lepus capensis also inhabiting warm climates. In conclusion, our results suggest that Cretan European hare populations exhibit a reproductively active period during autumn–early winter where proportions of pregnant females and litter size give a strong indication of a continuous reproduction throughout the year.     

Application of an improved continuous parallel shaken bioreactor system for three microbial model systems

A continuous parallel shaken bioreactor system, combining the advantages of shaken bioreactors with the advantages of continuous fermentation, was specifically manufactured from quartz glass and provides a geometric accuracy of <1 mm. Two different model systems (facultative anaerobic bacterium C. glutamicum, and Crabtree-negative yeast P. stipitis), whose growth behaviour and metabolite formation are affected by dilution rate and oxygen availability, were studied. The transition from non-oxygen to limited conditions as function of the dilution rate could precisely be predicted applying the approach described by Maier et al. (Biochem Eng J 17:155–167, 2004). In addition, the Crabtree-positive yeast S. cerevisiae was simultaneously studied in the continuous parallel shaken bioreactor system and in a conventional 1-L bioreactor, for comparison. Essentially the same results were obtained in both types of bioreactors. However, many more reading points were obtained with the parallel shaken bioreactor system in the same time at much lower consumption of culture media.     

Study of the Operability of a Continuous Bioreactor for the Pre‐fermentation of Cheese Culture

The dynamics of a continuous stirred‐tank bioreactor for cheese pre‐fermentation is analyzed using elementary concepts of bifurcation theory and continuation techniques. The bioreactor model, which was previously developed and validated, explicitly incorporates the effect of uncontrolled pH levels. The stability analysis of the model is carried out for two cases: In the first case, the bioreactor is equipped with a seed tank, while the second case involves no additional seed tank. The static analysis allows useful analytical results for the study of steady state multiplicity of the model to be derived. The results of this paper provide practical guidelines on the selection of operating parameters that can eliminate difficult operating regions and that can consequently improve the operability of the bioreactor.     

Uses and misuses of progress curve analysis in enzyme kinetics

Progress curve analysis is a convenient tool for the characterization of enzyme action: a single reaction mixture provides multiple experimental measured points for continuously varying amounts of substrates and products with exactly the same enzyme and modulator concentrations. The determination of kinetic parameters from the progress curves, however, requires complex mathematical evaluation of the time-course data. Some freely available programs (e.g. FITSIM, DYNAFIT) are widely applied to fit kinetic parameters to user-defined enzymatic mechanisms, but users often overlook the stringent requirements of the analytic procedures for appropriate design of the input experiments. Flaws in the experimental setup result in unreliable parameters with consequent misinterpretation of the biological phenomenon under study. The present commentary suggests some helpful mathematical tools to improve the analytic procedure in order to diagnose major errors in concept and design of kinetic experiments.     

Lipase-catalyzed selective synthesis of monolauroyl maltose using continuous stirred tank reactor

Monolauroyl maltose was synthesized by an immobilized lipase that catalyzed condensation of maltose and lauric acid in acetone using a batch reactor or a continuous stirred tank reactor. Mono- and di-lauroyl maltoses were identified by FT-IR, ¹H NMR, ¹³C NMR and MS. Monolauroyl maltose was selectively synthesized in a continuous stirred tank reactor and no diester was detected. The highest concentration of monolauroyl maltose at 28 mmol/l was obtained in 250 ml acetone when maltose was added at 4 g/d and the molar ratio of lauric acid to maltose was fixed at 4:1 at a flow rate of 0.15 ml/min for both influx and effluent without supplement of fresh molecular sieve.     

Partial nitrification to nitrite using low dissolved oxygen concentration as the main selection factor

Partial nitrification to nitrite (nitritation) can be achieved in a continuous process without sludge retention by wash out of nitrite oxidising bacteria (NOB) while retaining ammonia oxidising bacteria (AOB), at elevated temperatures (the SHARON process) and, as demonstrated in this paper, also at low dissolved oxygen (DO) concentrations. Enriched AOB was attained at a low DO concentration (0.4 mg l⁻¹) and a dilution rate of 0.42 day⁻¹ in a continuous process. A higher oxygen affinity of AOB compared to NOB seemed critical to achieving this. This was verified by determining the oxygen half saturation constant, K _o, with similar oxygen mass transfer resistances for enriched AOB and NOB as 0.033 ± 0.003 mg l⁻¹ and 0.43 ± 0.08 mg l⁻¹, respectively. However, the extent of nitritation attained was found to be highly sensitive to process upsets.     

Bio-oxidation of tripropylene glycol under aerobic conditions

Aerobic biodegradation of tripropylene glycol (PG3) was investigated under the conditions of the OECD screening test 301E and the Continuous Flow Activated Sludge Simulation test (CFAS). A modified two-chamber facility with a denitrification stage was used for the CFAS test. Primary PG3 biodegradation was measured by the HPLC with fluorimetric detection and analyte derivatisation. Metabolites were identified by LC-MS with electrospray ionisation and GC-MS with electron impact ionisation, as well as semiquantitatively determined by the LC-MS technique. PG3 was found to be inherently biodegradable and it exhibits a strong poisonous effect on activated sludge after exceeding the threshold concentration (10 mg l⁻¹). Metabolite accumulation onto the activated sludge is probably responsible for this poisonous effect. Probable biotransformation products of tripropylene glycol under the aerobic conditions include metabolites with a single terminal aldehyde or a ketone group and metabolites with two terminal aldehyde or ketone groups. Their concentration rises at the end of the OECD screening test.