Springtail postmolt vulnerability to pseudoscorpion predation: Mechanisms and implications

Arthropod prey are expected to be more vulnerable to their predators immediately following molt. The effects of springtail (Isotoma carpenteri) postmolt vulnerability on interactions with a pseudoscorpion predator were examined in the laboratory. Springtails exposed to vials pretreated with pseudoscorpions (Apochthonius minimus) delayed molting compared to those prey that were exposed to vials pretreated only with springtails. Although their escape ability (measured as distance jumped) was unaffected by molt condition, postmolt springtails were more profitable in terms of reduced predator handling time following capture. Despite this,A. minimus did not distinguish between postmolt and intermolt prey presented at either end of a T-maze.     

Homogenisation and oxygen transfer rates in large agitated and sparged animal cell bioreactors: Some implications for growth and production

Because of concern for cell damage, very low agitation energy inputs have been used in industrial animal cell bioreactors, typical values being two orders of magnitude less than those found in bacterial fermentations. Aeration rates are also very small. As a result, such bioreactors might be both poorly mixed and also unable to provide the higher oxygen up-take rates demanded by more intensive operation. This paper reports experimental studies both of K _L a and of mixing (via pH measurements) in bioreactors up to 8 m³ at Wellcome and of scaled down models of such reactors at Birmingham. Alongside these physical measurements, sensitivity of certain cell lines to continuously controlled dO₂ has been studied and the oxygen up-take rates measured in representative growth conditions. An analysis of characteristic times and mixing theory, together with other recent work showing that more vigorous agitation and aeration can be used especially in the presence of Pluronic F-68, indicates ways of improving their performance. pH gradients offer a special challenge.     

Search for rhythmicity during hibernation in the European hamster

Temporal patterns of hibernation were studied by continuous monitoring of body temperature by radiotelemetry over 6 months in European hamsters, Cricetus cricetus, at constant temperature and photoperiod. Entrances into hibernation occurred mostly at the end of the night (0000–0800 hours), while arousals were randomly distributed between day and night. This is at variance with a control of bout duration by a clock with a period of 24 h. Consequently, the timing of entrances implies a phase-resetting of the circadian clock on each arousal. Persistence of circadian rhythmicity with a period different from 24 h during deep hibernation was investigated examining whether the durations of torpor bouts were integer multiples of a constant period. A non-parametric version of the classical contingency test of periodicity was developed for this purpose. Periods ranging from 21 to 29 h were tested. Nine animals out of ten showed at least one significant period in this range (P<0.01), either below 24 h (21.8±0.5 h, n=4) or above (27.3±0.5 h, n=7). However, we have found a theoretical model of bout durations for which the contingency test of periodicity sometimes gives false significant results. This indicates that the power of the test is weak. With this reservation our results suggest that a circadian oscillator controls the duration of a bout of hibernation, which would occur after an integer, but variable and possibly temperature-dependent number of cycles.Abbreviations _b a contingency test (see Appendix) - SCN suprachiasmatic nuclei - period - T _b body temperature     

Times to exhaustion at 100% of velocity at [(V)\dot]\textO\text2 \dot V{\text{O}}_{\text{2}} max and modelling of the time-limit / velocity relationship in elite long-distance runners

The aim of this study was to measure running times to exhaustion (Tlim) on a treadmill at 100% of the minimum velocity which elicits _{max max} in 38 elite male long - distance runners _max = 71.4 ± 5.5 ml.kg^–1.min^–1 and _max = 21.8 ± 1.2 km.h^–1). The lactate threshold (LT) was defined as a starting point of accelerated lactate accumulation around 4 mM and was expressed in _max. Tlim value was negatively correlated with _max (r = -0.362, p< 0.05) and _max (r = –0.347, p< 0.05) but positively with LT (%v _max) (r = 0.378, p < 0.05). These data demonstrate that running time to exhaustion at _max in a homogeneous group of elite male long-distance runners was inversely related to _max and experimentally illustrates the model of Monod and Scherrer regarding the time limit-velocity relationship adapted from local exercise for running by Hughson et al. (1984) .     

Gut fluorescence in herbivorous copepods: an attempt to justify the method

Recently the gut fluorescence technique has been critisized because of the possible degradation of chlorophyll into nonfluorescent derivatives during passage through copepod guts and changes of the gut passage time with food concentration. Here pigment budgets have been calculated in 6 experiments with Calanus finmarchicus CIV caught 2 km offshore of the Murmansk Marine Biological Institute (the Barents Sea, Dalnije Zelentsi) in September 1992. Copepods were fed with culture of Platymonas viridis at different concentrations. Gut pigment and ingestion rate increased with food concentration in a similar way. On average between 78% and 89% of ingested chlorophyll was recovered in the guts and faecal pellets. No trend for a greater loss of fluorescence at low food concentration than at high was observed. Pigment content of faecal pellets incubated in filtered seawater decreased by 20–30% in the first 7–12 h and by up to 60% in 48 h. The decline of pigment content was accompanied by a rapid bacterial growth (by a factor of 3 in 48 h). Gut passage time increased with decreasing food concentration (from 40 min at 9 µg pigm l^–1 to 64 min at 0.9 µg pigm l^–1). These results together with some data by other authors suggest that the gut fluorescence method can be used to estimate in situ grazing rate providing gut passage time is measured properly and there are no losses of faecal material. However, careful consideration should be given to the previous feeding history of copepods.     

Anaerobic acidogenesis of primary sludge: the role of solids retention time

This research investigates the effect of solids retention time (SRT) on the acid-phase anaerobic digestion of primary sludge. A series of experiments were conducted using two continuous-flow 3-L units with the following configuration: a completely mixed reactor (CMR) with clarifier and solids recycle and an upflow anaerobic sludge blanket (UASB) reactor. Results show that C(2) to C(5) volatile fatty acids (VFA) were the predominant compounds formed. At a constant hydraulic retention time (HRT) of 12 h, variation in SRT from 10 to 20 days resulted in a slight increase in VFA production in both systems, but at a shorter SRT (5 days) a drastic drop in acid production was observed. In addition, the percent distribution of VFA was to some extent affected by the change in SRT. On the other hand, organic matter degradation [measured by the chemical oxygen demand (COD) specific solubilization rate or the percent volatile suspended solids (VSS) reduction] appeared to be independent of SRT, at least in the range investigated. The percent soluble COD in the form of VFA, however, increased steadily with increasing SRT, approaching the 90% level at 20 days. The remaining soluble COD in the effluent from these systems may be mainly attributed to metabolic intermediates and unused soluble substrate. (c) 1994 John Wiley & Sons, Inc.     

Biochemical diversity among sulfur-dependent, hyperthermophilic microorganisms

Abstract: Hyperthermophiles are a recently discovered group of microorganisms that grow at and above 90°C. They currently comprise over 20 different genera, and except for two novel bacteria, all are classified as Archaea. The majority of these organisms are obligately anaerobic heterotrophs that reduce elemental sulfur (S°) to H₂S. The best studied from a biochemical perspective are the archaeon, Pyrococcus furiosus , and the bacterium, Thermotoga maritima , both of which are saccharolytic. P. furiosus is thought to contain a new type of Entner-Doudoroff pathway for the conversion of carbohydrates ultimately to acetate, H₂ and CO₂. The pathway is independent of nicotinamide nucleotides and involves novel types of ferredoxin-linked oxidoreductases, one of which has tungsten, a rarely used element, as a prosthetic group. The only site of energy conservation is at the level of acetyl CoA, which in the presence of ADP and phosphate is converted to acetate and ATP in a single step. In contrast, T. maritima utilizes a conventional Embden-Meyerhof pathway for sugar oxidation. P. furiosus also utilizes peptides as a sole carbon and energy source. Amino acid oxidation is thought to involve glutamate dehydrogenase together with at least three types of novel ferredoxin-linked oxidoreductases which catalyze the oxidation of 2-ketoglutarate, aryl pyruvates and formaldehyde. One of these enzymes also utilizes tungsten. In P. furiosus , virtually all of the reductant that is generated during the catabolism of both carbohydrates and peptides is channeled to a cytoplasmic hydrogenase. This enzyme is now termed sulhydrogenase, as it reduces both protons to H₂ and S°(or polysulfide) to H₂S. S° reduction appears to lead to the conservation of energy in P. furiosus but not in T. maritima , although the mechanism by which this occurs is not known.     

Genes encoding homologues of three consecutive enzymes in the butyrate/butanol-producing pathway of Clostridium acetobutylicum are clustered on the Clostridium difficile chromosome

Abstract Screening of a Clostridium difficile ψEMBL3 gene library with antisera raised against C. difficile culture supernatant identified several clones expressing a 31-kDa protein. A 1.8-kb Hin dIII fragment subcloned from one of the clones was sufficient for expression of the 31-kDa polypeptide. Southern blot analysis showed a region homologous to this fragment to be present in all of 13 different C. difficile strains tested. Sequence analysis of the 1.8-kb fragment revealed three adjacent open reading frames. A database search showed that these three open reading frames appeared to encode homologues of three consecutive enzymes in the butanol/butyrate-producing pathway of Clostridium acetobutylicum (crotonase, β-hydroxybutyryl coenzyme A dehydrogenase and thiolase).     

湘北烟区烟青虫发生情况研究

烟青虫在湘北烟区1年发生5代,第一至四代危害烟草,第五代在其他作物上取食。自然条件下,世代重叠比较明显,幼虫发生与危害最大的是第一代,危害时期是5月下旬至6月下旬,同时,还得出了烟青虫各代的发生期、历期及其发育起点温度和有效积温。